Add some tests for the new executor system

And fix a couple of bugs picked up by said tests

build.gradle

@@ -42,6 +42,7 @@ minecraft {
 }
 
 repositories {
+    mavenLocal()
     maven {
         name = "JEI"
         url  = "http://dvs1.progwml6.com/files/maven"
@@ -66,7 +67,7 @@ dependencies {
 
     runtime "mezz.jei:jei_1.12.2:4.8.5.159"
 
-    shade 'org.squiddev:Cobalt:0.3.2'
+    shade 'org.squiddev:Cobalt:0.3.2-nothread'
 
     testCompile 'junit:junit:4.11'
 
@@ -196,3 +197,9 @@ gradle.projectsEvaluated {
 
 runClient.outputs.upToDateWhen { false }
 runServer.outputs.upToDateWhen { false }
+
+test {
+    testLogging {
+        events "failed", "standardOut", "standardError"
+    }
+}

src/main/java/dan200/computercraft/api/lua/ICallContext.java

@@ -0,0 +1,31 @@
+/*
+ * This file is part of the public ComputerCraft API - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
+ * For help using the API, and posting your mods, visit the forums at computercraft.info.
+ */
+
+package dan200.computercraft.api.lua;
+
+import javax.annotation.Nonnull;
+
+/**
+ * An interface passed to peripherals and {@link ILuaObject}s by computers or turtles, providing methods that allow the
+ * method to interact with the invoking computer.
+ */
+public interface ICallContext
+{
+    /**
+     * Queue a task to be executed on the main server thread at the beginning of next tick, but do not wait for it to
+     * complete. This should be used when you need to interact with the world in a thread-safe manner but do not care
+     * about the result or you wish to run asynchronously.
+     *
+     * When the task has finished, it will enqueue a {@code task_completed} event, which takes the task id, a success
+     * value and the return values, or an error message if it failed. If you need to wait on this event, it may be
+     * better to use {@link MethodResult#onMainThread(ILuaCallable)}.
+     *
+     * @param task The task to execute on the main thread.
+     * @return The "id" of the task. This will be the first argument to the {@code task_completed} event.
+     * @throws LuaException If the task could not be queued.
+     */
+    long issueMainThreadTask( @Nonnull ILuaTask task ) throws LuaException;
+}

src/main/java/dan200/computercraft/api/lua/ILuaCallable.java

@@ -0,0 +1,31 @@
+/*
+ * This file is part of the public ComputerCraft API - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
+ * For help using the API, and posting your mods, visit the forums at computercraft.info.
+ */
+
+package dan200.computercraft.api.lua;
+
+import javax.annotation.Nonnull;
+
+/**
+ * A function which calls performs an action in a specific context (such as on the server thread) and returns a result.
+ *
+ * @see MethodResult#onMainThread(ILuaCallable)
+ * @see ILuaContext#executeMainThreadTask(ILuaTask)
+ */
+@FunctionalInterface
+public interface ILuaCallable
+{
+    /**
+     * Run the code within the specified context and return the result to continue with.
+     *
+     * @return The result of executing this function. Note that this may not be evaluated within the same context as
+     * this call is.
+     * @throws LuaException If you throw any exception from this function, a lua error will be raised with the
+     *                      same message as your exception. Use this to throw appropriate errors if the wrong
+     *                      arguments are supplied to your method.
+     */
+    @Nonnull
+    MethodResult execute() throws LuaException;
+}

src/main/java/dan200/computercraft/api/lua/ILuaContext.java

@@ -1,6 +1,6 @@
 /*
  * This file is part of the public ComputerCraft API - http://www.computercraft.info
- * Copyright Daniel Ratcliffe, 2011-2017. This API may be redistributed unmodified and in full only.
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
  * For help using the API, and posting your mods, visit the forums at computercraft.info.
  */
 
@@ -13,8 +13,11 @@ import javax.annotation.Nullable;
  * An interface passed to peripherals and {@link ILuaObject}s by computers or turtles, providing methods
  * that allow the peripheral call to wait for events before returning, just like in lua. This is very useful if you need
  * to signal work to be performed on the main thread, and don't want to return until the work has been completed.
+ *
+ * This interface mostly exists for integrating with older code. One should use {@link MethodResult} instead, as this
+ * encourages an asynchronous way of interacting with Lua coroutines.
  */
-public interface ILuaContext
+public interface ILuaContext extends ICallContext
 {
     /**
      * Wait for an event to occur on the computer, suspending the thread until it arises. This method is exactly
@@ -30,8 +33,10 @@ public interface ILuaContext
      * @throws InterruptedException If the user shuts down or reboots the computer while pullEvent() is waiting for an
      *                              event, InterruptedException will be thrown. This exception must not be caught or
      *                              intercepted, or the computer will leak memory and end up in a broken state.
+     * @deprecated Use {@link MethodResult#pullEvent(String, ILuaFunction)}
      */
     @Nonnull
+    @Deprecated
     Object[] pullEvent( @Nullable String filter ) throws LuaException, InterruptedException;
 
     /**
@@ -45,8 +50,10 @@ public interface ILuaContext
      *                              an event, InterruptedException will be thrown. This exception must not be caught or
      *                              intercepted, or the computer will leak memory and end up in a broken state.
      * @see #pullEvent(String)
+     * @deprecated Use {@link MethodResult#pullEventRaw(String, ILuaFunction)}
      */
     @Nonnull
+    @Deprecated
     Object[] pullEventRaw( @Nullable String filter ) throws InterruptedException;
 
     /**
@@ -59,8 +66,10 @@ public interface ILuaContext
      *                              InterruptedException will be thrown. This exception must not be caught or
      *                              intercepted, or the computer will leak memory and end up in a broken state.
      * @see #pullEvent(String)
+     * @deprecated Use {@link MethodResult#pullEventRaw(ILuaFunction)}
      */
     @Nonnull
+    @Deprecated
     Object[] yield( @Nullable Object[] arguments ) throws InterruptedException;
 
     /**
@@ -76,22 +85,9 @@ public interface ILuaContext
      * @throws InterruptedException If the user shuts down or reboots the computer the coroutine is suspended,
      *                              InterruptedException will be thrown. This exception must not be caught or
      *                              intercepted, or the computer will leak memory and end up in a broken state.
+     * @deprecated Use {@link MethodResult#onMainThread(ILuaCallable)}
      */
     @Nullable
+    @Deprecated
     Object[] executeMainThreadTask( @Nonnull ILuaTask task ) throws LuaException, InterruptedException;
-
-    /**
-     * Queue a task to be executed on the main server thread at the beginning of next tick, but do not wait for it to
-     * complete. This should be used when you need to interact with the world in a thread-safe manner but do not care
-     * about the result or you wish to run asynchronously.
-     *
-     * When the task has finished, it will enqueue a {@code task_completed} event, which takes the task id, a success
-     * value and the return values, or an error message if it failed. If you need to wait on this event, it may be
-     * better to use {@link #executeMainThreadTask(ILuaTask)}.
-     *
-     * @param task The task to execute on the main thread.
-     * @return The "id" of the task. This will be the first argument to the {@code task_completed} event.
-     * @throws LuaException If the task could not be queued.
-     */
-    long issueMainThreadTask( @Nonnull ILuaTask task ) throws LuaException;
 }

src/main/java/dan200/computercraft/api/lua/ILuaContextTask.java

@@ -0,0 +1,24 @@
+/*
+ * This file is part of the public ComputerCraft API - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
+ * For help using the API, and posting your mods, visit the forums at computercraft.info.
+ */
+
+package dan200.computercraft.api.lua;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * A function which executes using a {@link ILuaContext}.
+ *
+ * Like {@link ILuaContext}, this is not intended for use in the future - it purely exists as an argument for
+ * {@link MethodResult#withLuaContext(ILuaContextTask)}.
+ */
+@FunctionalInterface
+public interface ILuaContextTask
+{
+    @Nullable
+    @Deprecated
+    Object[] execute( @Nonnull ILuaContext context ) throws LuaException, InterruptedException;
+}

src/main/java/dan200/computercraft/api/lua/ILuaFunction.java

@@ -0,0 +1,33 @@
+/*
+ * This file is part of the public ComputerCraft API - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
+ * For help using the API, and posting your mods, visit the forums at computercraft.info.
+ */
+
+package dan200.computercraft.api.lua;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * A Lua function which consumes some values and returns a result.
+ *
+ * @see MethodResult#then(ILuaFunction)
+ * @see MethodResult#pullEvent(ILuaFunction)
+ * @see MethodResult#pullEventRaw(String)
+ */
+@FunctionalInterface
+public interface ILuaFunction
+{
+    /**
+     * Accept the values and return another method result.
+     *
+     * @param values The inputs for this function.
+     * @return The result of executing this function.
+     * @throws LuaException If you throw any exception from this function, a lua error will be raised with the
+     *                      same message as your exception. Use this to throw appropriate errors if the wrong
+     *                      arguments are supplied to your method.
+     */
+    @Nonnull
+    MethodResult call( @Nullable Object[] values ) throws LuaException;
+}

src/main/java/dan200/computercraft/api/lua/ILuaObject.java

@@ -1,6 +1,6 @@
 /*
  * This file is part of the public ComputerCraft API - http://www.computercraft.info
- * Copyright Daniel Ratcliffe, 2011-2017. This API may be redistributed unmodified and in full only.
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
  * For help using the API, and posting your mods, visit the forums at computercraft.info.
  */
 
@@ -41,16 +41,45 @@ public interface ILuaObject
      *                  wishes to call. The integer indicates the index into the getMethodNames() table
      *                  that corresponds to the string passed into peripheral.call()
      * @param arguments The arguments for this method. See {@link IPeripheral#callMethod(IComputerAccess, ILuaContext, int, Object[])}
-     *                  the possible values and conversion rules.
-     * @return An array of objects, representing the values you wish to return to the Lua program.
-     * See {@link IPeripheral#callMethod(IComputerAccess, ILuaContext, int, Object[])} for the valid values and
-     * conversion rules.
-     * @throws LuaException         If the task could not be queued, or if the task threw an exception.
+     *                  for the possible values and conversion rules.
+     * @return An array of objects, representing the values you wish to return to the Lua program. See
+     * {@link MethodResult#of(Object...)}  for the valid values and conversion rules.
+     * @throws LuaException         If you throw any exception from this function, a lua error will be raised with the
+     *                              same message as your exception. Use this to throw appropriate errors if the wrong
+     *                              arguments are supplied to your method.
      * @throws InterruptedException If the user shuts down or reboots the computer the coroutine is suspended,
      *                              InterruptedException will be thrown. This exception must not be caught or
-     *                              intercepted, or the computer will leak memory and end up in a broken state.w
+     *                              intercepted, or the computer will leak memory and end up in a broken state.
      * @see IPeripheral#callMethod(IComputerAccess, ILuaContext, int, Object[])
+     * @deprecated Use {@link #callMethod(ICallContext, int, Object[])} instead.
      */
     @Nullable
+    @Deprecated
     Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException;
+
+    /**
+     * Called when a user calls one of the methods that this object implements. This works the same as
+     * {@link IPeripheral#callMethod(IComputerAccess, ICallContext, int, Object[])}}. See that method for detailed
+     * documentation.
+     *
+     * @param context   The context of the current call.
+     * @param method    An integer identifying which of the methods from getMethodNames() the computercraft
+     *                  wishes to call. The integer indicates the index into the getMethodNames() table
+     *                  that corresponds to the string passed into peripheral.call()
+     * @param arguments The arguments for this method. See {@link IPeripheral#callMethod(IComputerAccess, ICallContext, int, Object[])}
+     *                  for the possible values and conversion rules.
+     * @return The result of calling this method. Use {@link MethodResult#empty()} to return nothing or
+     * {@link MethodResult#of(Object...)} to return several values.
+     * @throws LuaException         If you throw any exception from this function, a lua error will be raised with the
+     *                              same message as your exception. Use this to throw appropriate errors if the wrong
+     *                              arguments are supplied to your method.
+     * @see IPeripheral#callMethod(IComputerAccess, ICallContext, int, Object[])
+     * @see MethodResult
+     */
+    @Nonnull
+    @SuppressWarnings( { "deprecation" } )
+    default MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
+    {
+        return MethodResult.withLuaContext( lua -> callMethod( lua, method, arguments ) );
+    }
 }

src/main/java/dan200/computercraft/api/lua/LuaContextResultEvaluator.java

@@ -0,0 +1,105 @@
+/*
+ * This file is part of the public ComputerCraft API - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
+ * For help using the API, and posting your mods, visit the forums at computercraft.info.
+ */
+
+package dan200.computercraft.api.lua;
+
+import javax.annotation.Nonnull;
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * Evaluates {@link MethodResult}s within a {@link ILuaContext}.
+ *
+ * @see MethodResult#evaluate(ILuaContext)
+ * @see MethodResult#withLuaContext(ILuaContextTask)
+ * @deprecated This should not be used except to interface between the two call call systems.
+ */
+@Deprecated
+class LuaContextResultEvaluator
+{
+    @Deprecated
+    public static Object[] evaluate( @Nonnull ILuaContext context, @Nonnull MethodResult future ) throws LuaException, InterruptedException
+    {
+        Deque<ILuaFunction> callbacks = null;
+        while( true )
+        {
+            if( future instanceof MethodResult.AndThen )
+            {
+                MethodResult.AndThen then = ((MethodResult.AndThen) future);
+
+                // Thens are "unwrapped", being pushed onto a stack
+                if( callbacks == null ) callbacks = new ArrayDeque<>();
+                callbacks.addLast( then.getCallback() );
+
+                future = then.getPrevious();
+                if( future == null ) throw new NullPointerException( "Null result from " + then.getCallback() );
+            }
+            else if( future instanceof MethodResult.Immediate )
+            {
+                Object[] values = ((MethodResult.Immediate) future).getResult();
+
+                // Immediate values values will attempt to call the previous "then", or return if nothing 
+                // else needs to be done.
+                ILuaFunction callback = callbacks == null ? null : callbacks.pollLast();
+                if( callback == null ) return values;
+
+                future = callback.call( values );
+                if( future == null ) throw new NullPointerException( "Null result from " + callback );
+            }
+            else if( future instanceof MethodResult.OnEvent )
+            {
+                MethodResult.OnEvent onEvent = (MethodResult.OnEvent) future;
+
+                // Poll for an event, and then call the previous "then" or return if nothing else needs 
+                // to be done. 
+                Object[] values = onEvent.isRaw() ? context.pullEventRaw( onEvent.getFilter() ) : context.pullEvent( onEvent.getFilter() );
+
+                ILuaFunction callback = callbacks == null ? null : callbacks.pollLast();
+                if( callback == null ) return values;
+
+                future = callback.call( values );
+                if( future == null ) throw new NullPointerException( "Null result from " + callback );
+            }
+            else if( future instanceof MethodResult.OnMainThread )
+            {
+                MethodResult.OnMainThread onMainThread = (MethodResult.OnMainThread) future;
+
+                // Evaluate our task on the main thread and mark it as the next future to evaluate.
+                Reference temporary = new Reference();
+                context.executeMainThreadTask( () -> {
+                    temporary.value = onMainThread.getTask().execute();
+                    return null;
+                } );
+
+                future = temporary.value;
+                if( future == null ) throw new NullPointerException( "Null result from " + onMainThread.getTask() );
+            }
+            else if( future instanceof MethodResult.WithLuaContext )
+            {
+                MethodResult.WithLuaContext withContext = (MethodResult.WithLuaContext) future;
+
+                // Run the task, and then call the previous "then" or return if nothing else
+                // needs to be done. 
+                Object[] values = withContext.getConsumer().execute( context );
+
+                ILuaFunction callback = callbacks == null ? null : callbacks.pollLast();
+                if( callback == null ) return values;
+                
+                future = callback.call( values );
+                if( future == null ) throw new NullPointerException( "Null result from " + callback );
+            }
+            else
+            {
+                throw new IllegalStateException( "Unknown MethodResult " + future );
+            }
+        }
+    }
+
+    private static class Reference
+    {
+        MethodResult value;
+    }
+}

src/main/java/dan200/computercraft/api/lua/MethodResult.java

@@ -0,0 +1,354 @@
+/*
+ * This file is part of the public ComputerCraft API - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
+ * For help using the API, and posting your mods, visit the forums at computercraft.info.
+ */
+
+package dan200.computercraft.api.lua;
+
+import com.google.common.base.Preconditions;
+import com.google.common.util.concurrent.ListenableFuture;
+import dan200.computercraft.api.peripheral.IComputerAccess;
+import dan200.computercraft.api.peripheral.IPeripheral;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.Map;
+
+/**
+ * The result of calling a method, such as {@link ILuaObject#callMethod(ICallContext, int, Object[])} or
+ * {@link IPeripheral#callMethod(IComputerAccess, ICallContext, int, Object[])}.
+ *
+ * This is non-dissimilar to a promise or {@link ListenableFuture}. One can either return an immediate value through
+ * {@link #of(Object...)}, wait for an external action with {@link #onMainThread(ILuaCallable)} or {@link #pullEvent()}
+ * and then act on the result of either of those by using {@link #then(ILuaFunction)}.
+ */
+public abstract class MethodResult
+{
+    private static MethodResult empty;
+
+    MethodResult()
+    {
+    }
+
+    /**
+     * A result which returns immediately with no value.
+     *
+     * Use {@link #of(Object...)} if you need to return one or more values.
+     *
+     * @return The empty method result.
+     * @see #of(Object...)
+     */
+    @Nonnull
+    public static MethodResult empty()
+    {
+        if( empty == null ) empty = new Immediate( null );
+        return empty;
+    }
+
+    /**
+     * A result which returns several values.
+     *
+     * @param result The values to return, this may be {@code null}. {@link Number}s, {@link String}s, {@link Boolean}s,
+     *               {@link Map}s, {@link ILuaObject}s, and {@code null} be converted to their corresponding lua type.
+     *               All other types will be converted to nil.
+     * @return A result which will return these values when evaluated.
+     * @see #empty()
+     */
+    @Nonnull
+    public static MethodResult of( Object... result )
+    {
+        return result == null ? empty() : new Immediate( result );
+    }
+
+    /**
+     * Wait for an event to occur on the computer, suspending the coroutine until it arises. This method is equivalent
+     * to {@code os.pullEvent()} in Lua.
+     *
+     * Normally you'll wish to consume the event using {@link #then(ILuaFunction)}. This can be done slightly more
+     * easily with {@link #pullEvent(ILuaFunction)}.
+     *
+     * If you want to listen to a specific event, it's easier to use {@link #pullEvent(String)} rather than
+     * running until the desired event is found.
+     *
+     * @return The constructed method result. This evaluates to the name of the event that occurred, and any event
+     * parameters.
+     * @see #pullEvent(ILuaFunction)
+     * @see #pullEvent(String)
+     */
+    @Nonnull
+    public static MethodResult pullEvent()
+    {
+        return new OnEvent( false, null );
+    }
+
+    /**
+     * Wait for the specified event to occur on the computer, suspending the coroutine until it arises. This method is
+     * equivalent to {@code os.pullEvent(event)} in Lua.
+     *
+     * Normally you'll wish to consume the event using {@link #then(ILuaFunction)}. This can be done slightly more
+     * easily with {@link #pullEvent(String, ILuaFunction)}.
+     *
+     * @param filter The event name to filter on.
+     * @return The constructed method result. This evaluates to the name of the event that occurred, and any event
+     * parameters.
+     * @see #pullEvent(String, ILuaFunction)
+     * @see #pullEvent()
+     */
+    @Nonnull
+    public static MethodResult pullEvent( @Nonnull String filter )
+    {
+        Preconditions.checkNotNull( filter, "event cannot be null" );
+        return new OnEvent( false, filter );
+    }
+
+    /**
+     * Wait for an event to occur on the computer, suspending the coroutine until it arises. This method to
+     * {@link #pullEvent()} and {@link #then(ILuaFunction)}.
+     *
+     * If you want to listen to a specific event, it's easier to use {@link #pullEvent(String, ILuaFunction)} rather
+     * than running until the desired event is found.
+     *
+     * @param callback The function to call when the event is received.
+     * @return The constructed method result. This evaluates to the result of the {@code callback}.
+     * @see #pullEvent()
+     * @see #pullEvent(String, ILuaFunction)
+     */
+    @Nonnull
+    public static MethodResult pullEvent( @Nonnull ILuaFunction callback )
+    {
+        Preconditions.checkNotNull( callback, "callback cannot be null" );
+        return new OnEvent( false, null ).then( callback );
+    }
+
+    /**
+     * Wait for the specified event to occur on the computer, suspending the coroutine until it arises. This method to
+     * {@link #pullEvent(String)} and {@link #then(ILuaFunction)}.
+     *
+     * @param filter   The event name to filter on.
+     * @param callback The function to call when the event is received.
+     * @return The constructed method result. This evaluates to the result of the {@code callback}.
+     * @see #pullEvent(String)
+     * @see #pullEvent(ILuaFunction)
+     */
+    @Nonnull
+    public static MethodResult pullEvent( @Nullable String filter, @Nonnull ILuaFunction callback )
+    {
+        Preconditions.checkNotNull( callback, "callback cannot be null" );
+        return new OnEvent( false, filter ).then( callback );
+    }
+
+    /**
+     * The same as {@link #pullEvent()}, except {@code terminated} events are also passed to the callback, instead of
+     * throwing an error. Only use this if you want to prevent program termination, which is not recommended.
+     *
+     * @return The constructed method result. This evaluates to the name of the event that occurred, and any event
+     * parameters.
+     */
+    @Nonnull
+    public static MethodResult pullEventRaw()
+    {
+        return new OnEvent( true, null );
+    }
+
+    /**
+     * The same as {@link #pullEvent(String)}, except {@code terminated} events are also passed to the callback, instead
+     * of throwing an error. Only use this if you want to prevent program termination, which is not recommended.
+     *
+     * @param filter The event name to filter on.
+     * @return The constructed method result. This evaluates to the name of the event that occurred, and any event
+     * parameters.
+     */
+    @Nonnull
+    public static MethodResult pullEventRaw( @Nonnull String filter )
+    {
+        return new OnEvent( true, filter );
+    }
+
+    /**
+     * The same as {@link #pullEvent(ILuaFunction)}, except {@code terminated} events are also passed to the callback,
+     * instead of throwing an error. Only use this if you want to prevent program termination, which is not recommended.
+     *
+     * @param callback The function to call when the event is received.
+     * @return The constructed method result. This evaluates to the result of the {@code callback}.
+     */
+    @Nonnull
+    public static MethodResult pullEventRaw( @Nonnull ILuaFunction callback )
+    {
+        Preconditions.checkNotNull( callback, "callback cannot be null" );
+        return new OnEvent( true, null ).then( callback );
+    }
+
+    /**
+     * The same as {@link #pullEvent(String, ILuaFunction)}, except {@code terminated} events are also passed to the
+     * callback, instead of throwing an error. Only use this if you want to prevent program termination, which is not
+     * recommended.
+     *
+     * @param filter   The event name to filter on.
+     * @param callback The function to call when the event is received.
+     * @return The constructed method result. This evaluates to the result of the {@code callback}.
+     */
+    @Nonnull
+    public static MethodResult pullEventRaw( @Nullable String filter, @Nonnull ILuaFunction callback )
+    {
+        Preconditions.checkNotNull( callback, "callback cannot be null" );
+        return new OnEvent( true, filter ).then( callback );
+    }
+
+    /**
+     * Queue a task to be executed on the main server thread at the beginning of next tick, waiting for it to complete.
+     * This should be used when you need to interact with the world in a thread-safe manner.
+     *
+     * @param callback The task to execute on the server thread.
+     * @return The constructed method result, which evaluates to the result of the {@code callback}.
+     */
+    @Nonnull
+    public static MethodResult onMainThread( @Nonnull ILuaCallable callback )
+    {
+        Preconditions.checkNotNull( callback, "callback cannot be null" );
+        return new OnMainThread( callback );
+    }
+
+    /**
+     * Consume the result of this {@link MethodResult} and return another result.
+     *
+     * Note this does NOT modify the current method result, rather returning a new (wrapped) one. You must return the
+     * result of this call if you wish to use it.
+     *
+     * @param callback The function which consumes the provided values.
+     * @return The constructed method result.
+     */
+    @Nonnull
+    public final MethodResult then( @Nonnull ILuaFunction callback )
+    {
+        Preconditions.checkNotNull( callback, "callback cannot be null" );
+        return new AndThen( this, callback );
+    }
+
+    /**
+     * Execute a blocking task within a {@link ILuaContext} and return its result.
+     *
+     * @param consumer The task to execute with the provided Lua context.
+     * @return The constructed method result.
+     * @see #evaluate(ILuaContext)
+     * @deprecated This should not be used except to interface between the two call systems.
+     */
+    @Deprecated
+    public static MethodResult withLuaContext( @Nonnull ILuaContextTask consumer )
+    {
+        Preconditions.checkNotNull( consumer, "consumer cannot be null" );
+        return new WithLuaContext( consumer );
+    }
+
+    /**
+     * Evaluate this result task using {@link ILuaContext} and return its result.
+     *
+     * @param context The context to execute with.
+     * @return The resulting values.
+     * @throws LuaException         If an error was thrown while executing one of the methods within this future.
+     * @throws InterruptedException If the user shuts down or reboots the computer while the coroutine is suspended.
+     * @see #withLuaContext(ILuaContextTask)
+     * @deprecated This should not be used except to interface between the two call systems.
+     */
+    @Deprecated
+    public final Object[] evaluate( @Nonnull ILuaContext context ) throws LuaException, InterruptedException
+    {
+        return LuaContextResultEvaluator.evaluate( context, this );
+    }
+
+    public static class Immediate extends MethodResult
+    {
+        @Nullable
+        private final Object[] values;
+
+        @Nullable
+        private Immediate( Object[] values )
+        {
+            this.values = values;
+        }
+
+        public Object[] getResult()
+        {
+            return values;
+        }
+    }
+
+    public static class OnEvent extends MethodResult
+    {
+        private final boolean raw;
+        private final String filter;
+
+        private OnEvent( boolean raw, String filter )
+        {
+            this.raw = raw;
+            this.filter = filter;
+        }
+
+        public boolean isRaw()
+        {
+            return raw;
+        }
+
+        @Nullable
+        public String getFilter()
+        {
+            return filter;
+        }
+    }
+
+    public static class OnMainThread extends MethodResult
+    {
+        private final ILuaCallable task;
+
+        public OnMainThread( ILuaCallable task )
+        {
+            this.task = task;
+        }
+
+        @Nonnull
+        public ILuaCallable getTask()
+        {
+            return task;
+        }
+    }
+
+    public static class AndThen extends MethodResult
+    {
+        private final MethodResult previous;
+        private final ILuaFunction callback;
+
+        private AndThen( MethodResult previous, ILuaFunction callback )
+        {
+            this.previous = previous;
+            this.callback = callback;
+        }
+
+        @Nonnull
+        public MethodResult getPrevious()
+        {
+            return previous;
+        }
+
+        @Nonnull
+        public ILuaFunction getCallback()
+        {
+            return callback;
+        }
+    }
+
+    public static class WithLuaContext extends MethodResult
+    {
+        private final ILuaContextTask consumer;
+
+        private WithLuaContext( ILuaContextTask consumer )
+        {
+            this.consumer = consumer;
+        }
+
+        @Nonnull
+        public ILuaContextTask getConsumer()
+        {
+            return consumer;
+        }
+    }
+}

src/main/java/dan200/computercraft/api/peripheral/IPeripheral.java

@@ -1,13 +1,15 @@
 /*
  * This file is part of the public ComputerCraft API - http://www.computercraft.info
- * Copyright Daniel Ratcliffe, 2011-2017. This API may be redistributed unmodified and in full only.
+ * Copyright Daniel Ratcliffe, 2011-2018. This API may be redistributed unmodified and in full only.
  * For help using the API, and posting your mods, visit the forums at computercraft.info.
  */
 
 package dan200.computercraft.api.peripheral;
 
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -70,10 +72,46 @@ public interface IPeripheral
      *                              InterruptedException will be thrown. This exception must not be caught or
      *                              intercepted, or the computer will leak memory and end up in a broken state.
      * @see #getMethodNames
+     * @deprecated Use {@link #callMethod(IComputerAccess, ICallContext, int, Object[])} instead.
      */
     @Nullable
+    @Deprecated
     Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException;
 
+    /**
+     * This is called when a lua program on an attached computer calls {@code peripheral.call()} with
+     * one of the methods exposed by {@link #getMethodNames()}.
+     *
+     * Be aware that this will be called from the ComputerCraft Lua thread, and must be thread-safe
+     * when interacting with Minecraft objects.
+     *
+     * @param computer  The interface to the computer that is making the call. Remember that multiple
+     *                  computers can be attached to a peripheral at once.
+     * @param context   The context of the current call.
+     * @param method    An integer identifying which of the methods from getMethodNames() the computercraft
+     *                  wishes to call. The integer indicates the index into the getMethodNames() table
+     *                  that corresponds to the string passed into peripheral.call()
+     * @param arguments An array of objects, representing the arguments passed into {@code peripheral.call()}.<br>
+     *                  Lua values of type "string" will be represented by Object type String.<br>
+     *                  Lua values of type "number" will be represented by Object type Double.<br>
+     *                  Lua values of type "boolean" will be represented by Object type Boolean.<br>
+     *                  Lua values of type "table" will be represented by Object type Map.<br>
+     *                  Lua values of any other type will be represented by a null object.<br>
+     *                  This array will be empty if no arguments are passed.
+     * @return The result of calling this method. Use {@link MethodResult#empty()} to return nothing or
+     * {@link MethodResult#of(Object...)} to return several values.
+     * @throws LuaException If you throw any exception from this function, a lua error will be raised with the
+     *                      same message as your exception. Use this to throw appropriate errors if the wrong
+     *                      arguments are supplied to your method.
+     * @see #getMethodNames
+     */
+    @Nonnull
+    @SuppressWarnings({ "deprecation" })
+    default MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
+    {
+        return MethodResult.withLuaContext( lua -> callMethod( computer, lua, method, arguments ) );
+    }
+
     /**
      * Is called when canAttachToSide has returned true, and a computer is attaching to the peripheral.
      *

src/main/java/dan200/computercraft/api/turtle/ITurtleAccess.java

@@ -9,6 +9,7 @@ package dan200.computercraft.api.turtle;
 import com.mojang.authlib.GameProfile;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import net.minecraft.inventory.IInventory;
 import net.minecraft.nbt.NBTTagCompound;
@@ -238,10 +239,30 @@ public interface ITurtleAccess
      *                                       intercepted, or the computer will leak memory and end up in a broken state.
      * @see ITurtleCommand
      * @see ILuaContext#pullEvent(String)
+     * @deprecated Use {@link #executeCommand(ITurtleCommand)} instead.
      */
     @Nonnull
+    @Deprecated
     Object[] executeCommand( @Nonnull ILuaContext context, @Nonnull ITurtleCommand command ) throws LuaException, InterruptedException;
 
+    /**
+     * Adds a custom command to the turtles command queue. Unlike peripheral methods, these custom commands will be
+     * executed on the main thread, so are guaranteed to be able to access Minecraft objects safely, and will be queued
+     * up with the turtles standard movement and tool commands.
+     *
+     * An issued command will return an unique integer, which will be supplied as a parameter to a "turtle_response"
+     * event issued to the turtle after the command has completed. Look at the Lua source code for "rom/apis/turtle" for
+     * how to build a Lua wrapper around this functionality.
+     *
+     * @param command An object which will execute the custom command when its point in the queue is reached
+     * @return The constructed method result. This evaluates to the result of the provided {@code command}.
+     * @throws UnsupportedOperationException When attempting to execute a command on the client side.
+     * @see ITurtleCommand
+     * @see MethodResult#pullEvent(String)
+     */
+    @Nonnull
+    MethodResult executeCommand( @Nonnull ITurtleCommand command );
+
     /**
      * Start playing a specific animation. This will prevent other turtle commands from executing until
      * it is finished.

src/main/java/dan200/computercraft/api/turtle/ITurtleUpgrade.java

@@ -133,7 +133,7 @@ public interface ITurtleUpgrade
      * @return The model that you wish to be used to render your upgrade, and a transformation to apply to it. Returning
      * a transformation of {@code null} has the same effect as the identify matrix.
      */
-    @SideOnly(Side.CLIENT)
+    @SideOnly( Side.CLIENT )
     @Nonnull
     Pair<IBakedModel, Matrix4f> getModel( @Nullable ITurtleAccess turtle, @Nonnull TurtleSide side );
 

src/main/java/dan200/computercraft/core/apis/BufferAPI.java

@@ -6,13 +6,12 @@
 
 package dan200.computercraft.core.apis;
 
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.ILuaObject;
-import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.core.terminal.TextBuffer;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.getString;
 import static dan200.computercraft.core.apis.ArgumentHelper.optInt;
@@ -41,27 +40,28 @@ public class BufferAPI implements ILuaAPI
             };
         }
 
+        @Nonnull
         @Override
-        public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+        public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
         {
             switch( method )
             {
                 case 0:
                 {
                     // len
-                    return new Object[] { m_buffer.length() };
+                    return MethodResult.of( m_buffer.length() );
                 }
                 case 1:
                 {
                     // tostring
-                    return new Object[] { m_buffer.toString() };
+                    return MethodResult.of( m_buffer.toString() );
                 }
                 case 2:
                 {
                     // read
                     int start = optInt( arguments, 0, 0 );
                     int end = optInt( arguments, 1, m_buffer.length() );
-                    return new Object[] { m_buffer.read( start, end ) };
+                    return MethodResult.of( m_buffer.read( start, end ) );
                 }
                 case 3:
                 {
@@ -70,7 +70,7 @@ public class BufferAPI implements ILuaAPI
                     int start = optInt( arguments, 1, 0 );
                     int end = optInt( arguments, 2, start + text.length() );
                     m_buffer.write( text, start, end );
-                    return null;
+                    return MethodResult.empty();
                 }
                 case 4:
                 {
@@ -79,14 +79,22 @@ public class BufferAPI implements ILuaAPI
                     int start = optInt( arguments, 1, 0 );
                     int end = optInt( arguments, 2, m_buffer.length() );
                     m_buffer.fill( text, start, end );
-                    return null;
+                    return MethodResult.empty();
                 }
                 default:
                 {
-                    return null;
+                    return MethodResult.empty();
                 }
             }
         }
+
+        @Nullable
+        @Override
+        @Deprecated
+        public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+        {
+            return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+        }
     }
 
     public BufferAPI( IAPIEnvironment _env )
@@ -110,8 +118,9 @@ public class BufferAPI implements ILuaAPI
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
     {
         switch( method )
         {
@@ -124,12 +133,20 @@ public class BufferAPI implements ILuaAPI
                     throw ArgumentHelper.badArgument( 1, "positive number", Integer.toString( repetitions ) );
                 }
                 TextBuffer buffer = new TextBuffer( text, repetitions );
-                return new Object[] { new BufferLuaObject( buffer ) };
+                return MethodResult.of( new BufferLuaObject( buffer ) );
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
 }

src/main/java/dan200/computercraft/core/apis/FSAPI.java

@@ -6,9 +6,8 @@
 
 package dan200.computercraft.core.apis;
 
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.core.apis.handles.BinaryInputHandle;
 import dan200.computercraft.core.apis.handles.BinaryOutputHandle;
 import dan200.computercraft.core.apis.handles.EncodedInputHandle;
@@ -18,6 +17,7 @@ import dan200.computercraft.core.filesystem.FileSystemException;
 import dan200.computercraft.core.tracking.TrackingField;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.HashMap;
@@ -80,8 +80,9 @@ public class FSAPI implements ILuaAPI
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -96,7 +97,7 @@ public class FSAPI implements ILuaAPI
                     for(int i=0; i<results.length; ++i ) {
                         table.put( i+1, results[i] );
                     }
-                    return new Object[] { table };
+                    return MethodResult.of( table );
                 }
                 catch( FileSystemException e )
                 {
@@ -108,13 +109,13 @@ public class FSAPI implements ILuaAPI
                 // combine
                 String pathA = getString( args, 0 );
                 String pathB = getString( args, 1 );
-                return new Object[] { m_fileSystem.combine( pathA, pathB ) };
+                return MethodResult.of( m_fileSystem.combine( pathA, pathB ) );
             }
             case 2:
             {
                 // getName
                 String path = getString( args, 0 );
-                return new Object[]{ FileSystem.getName( path ) };
+                return MethodResult.of( FileSystem.getName( path ) );
             }
             case 3:
             {
@@ -122,7 +123,7 @@ public class FSAPI implements ILuaAPI
                 String path = getString( args, 0 );
                 try
                 {
-                    return new Object[]{ m_fileSystem.getSize( path ) };
+                    return MethodResult.of( m_fileSystem.getSize( path ) );
                 }
                 catch( FileSystemException e )
                 {
@@ -134,9 +135,9 @@ public class FSAPI implements ILuaAPI
                 // exists
                 String path = getString( args, 0 );
                 try {
-                    return new Object[]{ m_fileSystem.exists( path ) };
+                    return MethodResult.of( m_fileSystem.exists( path ) );
                 } catch( FileSystemException e ) {
-                    return new Object[]{ false };
+                    return MethodResult.of( false );
                 }
             }
             case 5:
@@ -144,9 +145,9 @@ public class FSAPI implements ILuaAPI
                 // isDir
                 String path = getString( args, 0 );
                 try {
-                    return new Object[]{ m_fileSystem.isDir( path ) };
+                    return MethodResult.of( m_fileSystem.isDir( path ) );
                 } catch( FileSystemException e ) {
-                    return new Object[]{ false };
+                    return MethodResult.of( false );
                 }
             }
             case 6:
@@ -154,9 +155,9 @@ public class FSAPI implements ILuaAPI
                 // isReadOnly
                 String path = getString( args, 0 );
                 try {
-                    return new Object[]{ m_fileSystem.isReadOnly( path ) };
+                    return MethodResult.of( m_fileSystem.isReadOnly( path ) );
                 } catch( FileSystemException e ) {
-                    return new Object[]{ false };
+                    return MethodResult.of( false );
                 }
             }
             case 7:
@@ -166,7 +167,7 @@ public class FSAPI implements ILuaAPI
                 try {
                     m_env.addTrackingChange( TrackingField.FS_OPS );
                     m_fileSystem.makeDir( path );
-                    return null;
+                    return MethodResult.empty();
                 } catch( FileSystemException e ) {
                     throw new LuaException( e.getMessage() );
                 }
@@ -179,7 +180,7 @@ public class FSAPI implements ILuaAPI
                 try {
                     m_env.addTrackingChange( TrackingField.FS_OPS );
                     m_fileSystem.move( path, dest );
-                    return null;
+                    return MethodResult.empty();
                 } catch( FileSystemException e ) {
                     throw new LuaException( e.getMessage() );
                 }
@@ -192,7 +193,7 @@ public class FSAPI implements ILuaAPI
                 try {
                     m_env.addTrackingChange( TrackingField.FS_OPS );
                     m_fileSystem.copy( path, dest );
-                    return null;
+                    return MethodResult.empty();
                 } catch( FileSystemException e ) {
                     throw new LuaException( e.getMessage() );
                 }
@@ -204,7 +205,7 @@ public class FSAPI implements ILuaAPI
                 try {
                     m_env.addTrackingChange( TrackingField.FS_OPS );
                     m_fileSystem.delete( path );
-                    return null;
+                    return MethodResult.empty();
                 } catch( FileSystemException e ) {
                     throw new LuaException( e.getMessage() );
                 }
@@ -222,43 +223,43 @@ public class FSAPI implements ILuaAPI
                         {
                             // Open the file for reading, then create a wrapper around the reader
                             InputStream reader = m_fileSystem.openForRead( path );
-                            return new Object[] { new EncodedInputHandle( reader ) };
+                            return MethodResult.of( new EncodedInputHandle( reader ) );
                         }
                         case "w":
                         {
                             // Open the file for writing, then create a wrapper around the writer
                             OutputStream writer = m_fileSystem.openForWrite( path, false );
-                            return new Object[] { new EncodedOutputHandle( writer ) };
+                            return MethodResult.of( new EncodedOutputHandle( writer ) );
                         }
                         case "a":
                         {
                             // Open the file for appending, then create a wrapper around the writer
                             OutputStream writer = m_fileSystem.openForWrite( path, true );
-                            return new Object[] { new EncodedOutputHandle( writer ) };
+                            return MethodResult.of( new EncodedOutputHandle( writer ) );
                         }
                         case "rb":
                         {
                             // Open the file for binary reading, then create a wrapper around the reader
                             InputStream reader = m_fileSystem.openForRead( path );
-                            return new Object[] { new BinaryInputHandle( reader ) };
+                            return MethodResult.of( new BinaryInputHandle( reader ) );
                         }
                         case "wb":
                         {
                             // Open the file for binary writing, then create a wrapper around the writer
                             OutputStream writer = m_fileSystem.openForWrite( path, false );
-                            return new Object[] { new BinaryOutputHandle( writer ) };
+                            return MethodResult.of( new BinaryOutputHandle( writer ) );
                         }
                         case "ab":
                         {
                             // Open the file for binary appending, then create a wrapper around the reader
                             OutputStream writer = m_fileSystem.openForWrite( path, true );
-                            return new Object[] { new BinaryOutputHandle( writer ) };
+                            return MethodResult.of( new BinaryOutputHandle( writer ) );
                         }
                         default:
                             throw new LuaException( "Unsupported mode" );
                     }
                 } catch( FileSystemException e ) {
-                    return new Object[] { null, e.getMessage() };
+                    return MethodResult.of( null, e.getMessage() );
                 }
             }
             case 12:
@@ -268,9 +269,9 @@ public class FSAPI implements ILuaAPI
                 try {
                     if( !m_fileSystem.exists( path ) )
                     {
-                        return null;
+                        return MethodResult.empty();
                     }
-                    return new Object[]{ m_fileSystem.getMountLabel( path ) };
+                    return MethodResult.of( m_fileSystem.getMountLabel( path ) );
                 } catch( FileSystemException e ) {
                     throw new LuaException( e.getMessage() );
                 }
@@ -283,9 +284,9 @@ public class FSAPI implements ILuaAPI
                     long freeSpace = m_fileSystem.getFreeSpace( path );
                     if( freeSpace >= 0 )
                     {
-                        return new Object[]{ freeSpace };
+                        return MethodResult.of( freeSpace );
                     }
-                    return new Object[]{ "unlimited" };
+                    return MethodResult.of( "unlimited" );
                 } catch( FileSystemException e ) {
                     throw new LuaException( e.getMessage() );
                 }
@@ -301,7 +302,7 @@ public class FSAPI implements ILuaAPI
                     for(int i=0; i<results.length; ++i ) {
                         table.put( i+1, results[i] );
                     }
-                    return new Object[] { table };
+                    return MethodResult.of( table );
                 } catch( FileSystemException e ) {
                     throw new LuaException( e.getMessage() );
                 }
@@ -310,13 +311,21 @@ public class FSAPI implements ILuaAPI
             {
                 // getDir
                 String path = getString( args, 0 );
-                return new Object[]{ FileSystem.getDirectory( path ) };
+                return MethodResult.of( FileSystem.getDirectory( path ) );
             }
             default:
             {
                 assert( false );
-                return null;
+                return MethodResult.empty();
             }
         }
     }
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
 }

src/main/java/dan200/computercraft/core/apis/HTTPAPI.java

@@ -8,12 +8,12 @@ package dan200.computercraft.core.apis;
 
 import com.google.common.collect.ImmutableSet;
 import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.core.apis.http.*;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.io.Closeable;
 import java.io.IOException;
 import java.net.URI;
@@ -102,8 +102,9 @@ public class HTTPAPI implements ILuaAPI
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -164,11 +165,11 @@ public class HTTPAPI implements ILuaAPI
                     {
                         m_httpTasks.add( HTTPExecutor.EXECUTOR.submit( request ) );
                     }
-                    return new Object[]{ true };
+                    return MethodResult.of(true);
                 }
                 catch( HTTPRequestException e )
                 {
-                    return new Object[]{ false, e.getMessage() };
+                    return MethodResult.of( false, e.getMessage() );
                 }
             }
             case 1:
@@ -186,11 +187,11 @@ public class HTTPAPI implements ILuaAPI
                     {
                         m_httpTasks.add( HTTPExecutor.EXECUTOR.submit( check ) );
                     }
-                    return new Object[]{ true };
+                    return MethodResult.of( true );
                 }
                 catch( HTTPRequestException e )
                 {
-                    return new Object[]{ false, e.getMessage() };
+                    return MethodResult.of( false, e.getMessage() );
                 }
             }
             case 2: // websocket
@@ -223,20 +224,28 @@ public class HTTPAPI implements ILuaAPI
                     {
                         m_httpTasks.add( connector );
                     }
-                    return new Object[]{ true };
+                    return MethodResult.of(true);
                 }
                 catch( HTTPRequestException e )
                 {
-                    return new Object[]{ false, e.getMessage() };
+                    return MethodResult.of( false, e.getMessage() );
                 }
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
 
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
     public void addCloseable( Closeable closeable )
     {
         synchronized( m_closeables )

src/main/java/dan200/computercraft/core/apis/OSAPI.java

@@ -6,12 +6,12 @@
 
 package dan200.computercraft.core.apis;
 
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.shared.util.StringUtil;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.*;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.*;
@@ -221,7 +221,8 @@ public class OSAPI implements ILuaAPI
     }
 
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    @Nonnull
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -229,7 +230,7 @@ public class OSAPI implements ILuaAPI
             {
                 // queueEvent
                 queueLuaEvent( getString( args, 0 ), trimArray( args, 1 ) );
-                return null;
+                return MethodResult.empty();
             }
             case 1:
             {
@@ -238,7 +239,7 @@ public class OSAPI implements ILuaAPI
                 synchronized( m_timers )
                 {
                     m_timers.put( m_nextTimerToken, new Timer( (int)Math.round( timer / 0.05 ) ) );
-                    return new Object[] { m_nextTimerToken++ };
+                    return MethodResult.of( m_nextTimerToken++ );
                 }
             }
             case 2:
@@ -253,33 +254,33 @@ public class OSAPI implements ILuaAPI
                 {
                     int day = (time > m_time) ? m_day : (m_day + 1);
                     m_alarms.put( m_nextAlarmToken, new Alarm( time, day ) );
-                    return new Object[] { m_nextAlarmToken++ };
+                    return MethodResult.of( m_nextAlarmToken++ );
                 }
             }
             case 3:
             {
                 // shutdown
                 m_apiEnvironment.shutdown();
-                return null;
+                return MethodResult.empty();
             }
             case 4:
             {
                 // reboot
                 m_apiEnvironment.reboot();
-                return null;
+                return MethodResult.empty();
             }
             case 5:
             case 6:
             {
                 // computerID/getComputerID
-                return new Object[] { getComputerID() };
+                return MethodResult.of( getComputerID() );
             }
             case 7:
             {
                 // setComputerLabel
                 String label = optString( args, 0, null );
                 m_apiEnvironment.setLabel( StringUtil.normaliseLabel( label ) );
-                return null;
+                return MethodResult.empty();
             }
             case 8:
             case 9:
@@ -288,16 +289,16 @@ public class OSAPI implements ILuaAPI
                 String label = m_apiEnvironment.getLabel();
                 if( label != null )
                 {
-                    return new Object[] { label };
+                    return MethodResult.of( label );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 10:
             {
                 // clock
                 synchronized( m_timers )
                 {
-                    return new Object[] { m_clock * 0.05 };
+                    return MethodResult.of( m_clock * 0.05 );
                 }
             }
             case 11:
@@ -310,19 +311,19 @@ public class OSAPI implements ILuaAPI
                     {
                         // Get Hour of day (UTC)
                         Calendar c = Calendar.getInstance( TimeZone.getTimeZone( "UTC" ) );
-                        return new Object[] { getTimeForCalendar( c ) };
+                        return MethodResult.of( getTimeForCalendar( c ) );
                     }
                     case "local":
                     {
                         // Get Hour of day (local time)
                         Calendar c = Calendar.getInstance();
-                        return new Object[] { getTimeForCalendar( c ) };
+                        return MethodResult.of( getTimeForCalendar( c ) );
                     }
                     case "ingame":
                         // Get ingame hour
                         synchronized( m_alarms )
                         {
-                            return new Object[] { m_time };
+                            return MethodResult.of( m_time );
                         }
                     default:
                         throw new LuaException( "Unsupported operation" );
@@ -338,19 +339,19 @@ public class OSAPI implements ILuaAPI
                     {
                         // Get numbers of days since 1970-01-01 (utc)
                         Calendar c = Calendar.getInstance( TimeZone.getTimeZone( "UTC" ) );
-                        return new Object[] { getDayForCalendar( c ) };
+                        return MethodResult.of( getDayForCalendar( c ) );
                     }
                     case "local":
                     {
                         // Get numbers of days since 1970-01-01 (local time)
                         Calendar c = Calendar.getInstance();
-                        return new Object[] { getDayForCalendar( c ) };
+                        return MethodResult.of( getDayForCalendar( c ) );
                     }
                     case "ingame":
                         // Get game day
                         synchronized( m_alarms )
                         {
-                            return new Object[] { m_day };
+                            return MethodResult.of( m_day );
                         }
                     default:
                         throw new LuaException( "Unsupported operation" );
@@ -367,7 +368,7 @@ public class OSAPI implements ILuaAPI
                         m_timers.remove( token );
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 14:
             {
@@ -380,7 +381,7 @@ public class OSAPI implements ILuaAPI
                         m_alarms.remove( token );
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 15:
             {
@@ -392,21 +393,21 @@ public class OSAPI implements ILuaAPI
                     {
                         // Get utc epoch
                         Calendar c = Calendar.getInstance( TimeZone.getTimeZone( "UTC" ) );
-                        return new Object[] { getEpochForCalendar( c ) };
+                        return MethodResult.of( getEpochForCalendar( c ) );
                     }
                     case "local":
                     {
                         // Get local epoch
                         Calendar c = Calendar.getInstance();
-                        return new Object[] { getEpochForCalendar( c ) };
+                        return MethodResult.of( getEpochForCalendar( c ) );
                     }
                     case "ingame":
                         // Get in-game epoch
                         synchronized( m_alarms )
                         {
-                            return new Object[] {
+                            return MethodResult.of(
                                 m_day * 86400000 + (int) (m_time * 3600000.0f)
-                            };
+                            );
                         }
                     default:
                         throw new LuaException( "Unsupported operation" );
@@ -414,11 +415,18 @@ public class OSAPI implements ILuaAPI
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
 
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
     // Private methods
 
     private void queueLuaEvent( String event, Object[] args )

src/main/java/dan200/computercraft/core/apis/PeripheralAPI.java

@@ -8,9 +8,8 @@ package dan200.computercraft.core.apis;
 
 import dan200.computercraft.api.filesystem.IMount;
 import dan200.computercraft.api.filesystem.IWritableMount;
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.core.computer.Computer;
 import dan200.computercraft.core.computer.ComputerThread;
@@ -98,7 +97,7 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
             m_attached = false;
         }
 
-        public Object[] call( ILuaContext context, String methodName, Object[] arguments ) throws LuaException, InterruptedException
+        public MethodResult call( ICallContext context, String methodName, Object[] arguments ) throws LuaException
         {
             int method = -1;
             synchronized( this )
@@ -368,8 +367,9 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException, InterruptedException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -389,7 +389,7 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
                         }
                     }
                 }
-                return new Object[] { present };
+                return MethodResult.of( present );
             }
             case 1:
             {
@@ -408,10 +408,10 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
                     }
                     if( type != null )
                     {
-                        return new Object[] { type };
+                        return MethodResult.of( type );
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 2:
             {
@@ -435,9 +435,9 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
                     for(int i=0; i<methods.length; ++i ) {
                         table.put( i+1, methods[i] );
                     }
-                    return new Object[] { table };
+                    return MethodResult.of( table );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 3:
             {
@@ -462,11 +462,19 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
 
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
+    
     // Privates
 
     private int parseSide( Object[] args ) throws LuaException

src/main/java/dan200/computercraft/core/apis/RedstoneAPI.java

@@ -6,12 +6,12 @@
 
 package dan200.computercraft.core.apis;
 
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.core.computer.Computer;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -56,8 +56,9 @@ public class RedstoneAPI implements ILuaAPI
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -69,7 +70,7 @@ public class RedstoneAPI implements ILuaAPI
                 {
                     table.put( i+1, Computer.s_sideNames[i] );
                 }
-                return new Object[] { table };
+                return MethodResult.of( table );
             }
             case 1:
             {
@@ -77,19 +78,19 @@ public class RedstoneAPI implements ILuaAPI
                 int side = parseSide( args );
                 boolean output = getBoolean( args, 1 );
                 m_environment.setOutput( side, output ? 15 : 0 );
-                return null;
+                return MethodResult.empty();
             }
             case 2:
             {
                 // getOutput
                 int side = parseSide( args );
-                return new Object[] { m_environment.getOutput( side ) > 0 };
+                return MethodResult.of( m_environment.getOutput( side ) > 0 );
             }
             case 3:
             {
                 // getInput
                 int side = parseSide( args );
-                return new Object[] { m_environment.getInput( side ) > 0 };
+                return MethodResult.of( m_environment.getInput( side ) > 0 );
             }
             case 4:
             {
@@ -97,19 +98,19 @@ public class RedstoneAPI implements ILuaAPI
                 int side = parseSide( args );
                 int output = getInt( args, 1 );
                 m_environment.setBundledOutput( side, output );
-                return null;
+                return MethodResult.empty();
             }
             case 5:
             {
                 // getBundledOutput
                 int side = parseSide( args );
-                return new Object[] { m_environment.getBundledOutput( side ) };
+                return MethodResult.of( m_environment.getBundledOutput( side ) );
             }
             case 6:
             {
                 // getBundledInput
                 int side = parseSide( args );
-                return new Object[] { m_environment.getBundledInput( side ) };
+                return MethodResult.of( m_environment.getBundledInput( side ) );
             }
             case 7:
             {
@@ -117,7 +118,7 @@ public class RedstoneAPI implements ILuaAPI
                 int side = parseSide( args );
                 int mask = getInt( args, 1 );
                 int input = m_environment.getBundledInput( side );
-                return new Object[] { ((input & mask) == mask) };
+                return MethodResult.of( ((input & mask) == mask) );
             }
             case 8:
             case 9:
@@ -130,28 +131,36 @@ public class RedstoneAPI implements ILuaAPI
                     throw new LuaException( "Expected number in range 0-15" );
                 }
                 m_environment.setOutput( side, output );
-                return null;
+                return MethodResult.empty();
             }
             case 10:
             case 11:
             {
                 // getAnalogOutput/getAnalogueOutput
                 int side = parseSide( args );
-                return new Object[] { m_environment.getOutput( side ) };
+                return MethodResult.of( m_environment.getOutput( side ) );
             }
             case 12:
             case 13:
             {
                 // getAnalogInput/getAnalogueInput
                 int side = parseSide( args );
-                return new Object[] { m_environment.getInput( side ) };
+                return MethodResult.of( m_environment.getInput( side ) );
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
     
     private int parseSide( Object[] args ) throws LuaException
     {

src/main/java/dan200/computercraft/core/apis/TermAPI.java

@@ -6,15 +6,15 @@
 
 package dan200.computercraft.core.apis;
 
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.core.computer.IComputerEnvironment;
 import dan200.computercraft.core.terminal.Terminal;
 import dan200.computercraft.shared.util.Palette;
 import org.apache.commons.lang3.ArrayUtils;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.*;
 
@@ -83,11 +83,9 @@ public class TermAPI implements ILuaAPI
         return colour;
     }
 
-    public static Object[] encodeColour( int colour ) throws LuaException
+    public static MethodResult encodeColour( int colour )
     {
-        return new Object[] {
-            1 << colour
-        };
+        return MethodResult.of( 1 << colour );
     }
 
     public static void setColour( Terminal terminal, int colour, double r, double g, double b )
@@ -99,8 +97,9 @@ public class TermAPI implements ILuaAPI
         }
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -119,7 +118,7 @@ public class TermAPI implements ILuaAPI
                     m_terminal.write( text );
                     m_terminal.setCursorPos( m_terminal.getCursorX() + text.length(), m_terminal.getCursorY() );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 1:
             {
@@ -129,7 +128,7 @@ public class TermAPI implements ILuaAPI
                 {
                     m_terminal.scroll(y);
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 2:
             {
@@ -140,7 +139,7 @@ public class TermAPI implements ILuaAPI
                 {
                     m_terminal.setCursorPos( x, y );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 3:
             {
@@ -150,7 +149,7 @@ public class TermAPI implements ILuaAPI
                 {
                     m_terminal.setCursorBlink( b );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 4:
             {
@@ -161,7 +160,7 @@ public class TermAPI implements ILuaAPI
                     x = m_terminal.getCursorX();
                     y = m_terminal.getCursorY();
                 }
-                return new Object[] { x + 1, y + 1 };
+                return MethodResult.of( x + 1, y + 1 );
             }
             case 5:
             {
@@ -172,7 +171,7 @@ public class TermAPI implements ILuaAPI
                     width = m_terminal.getWidth();
                     height = m_terminal.getHeight();
                 }                
-                return new Object[] { width, height };
+                return MethodResult.of( width, height );
             }
             case 6:
             {
@@ -181,7 +180,7 @@ public class TermAPI implements ILuaAPI
                 {
                     m_terminal.clear();
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 7:
             {
@@ -190,7 +189,7 @@ public class TermAPI implements ILuaAPI
                 {
                     m_terminal.clearLine();
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 8:
             case 9:
@@ -201,7 +200,7 @@ public class TermAPI implements ILuaAPI
                 {
                     m_terminal.setTextColour( colour );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 10:
             case 11:
@@ -212,13 +211,13 @@ public class TermAPI implements ILuaAPI
                 {
                     m_terminal.setBackgroundColour( colour );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 12:
             case 13:
             {
                 // isColour/isColor
-                return new Object[] { m_environment.isColour() };
+                return MethodResult.of( m_environment.isColour() );
             }
             case 14:
             case 15:
@@ -248,7 +247,7 @@ public class TermAPI implements ILuaAPI
                     m_terminal.blit( text, textColour, backgroundColour );
                     m_terminal.setCursorPos( m_terminal.getCursorX() + text.length(), m_terminal.getCursorY() );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 19:
             case 20:
@@ -268,7 +267,7 @@ public class TermAPI implements ILuaAPI
                     double b = getReal( args, 3 );
                     setColour( m_terminal, colour, r, g, b );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 21:
             case 22:
@@ -279,18 +278,26 @@ public class TermAPI implements ILuaAPI
                 {
                     if ( m_terminal.getPalette() != null )
                     {
-                        return ArrayUtils.toObject( m_terminal.getPalette().getColour( colour ) );
+                        return MethodResult.of( (Object[]) ArrayUtils.toObject( m_terminal.getPalette().getColour( colour ) ) );
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
-    
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
     private static int getHighestBit( int group )
     {
         int bit = 0;

src/main/java/dan200/computercraft/core/apis/handles/BinaryInputHandle.java

@@ -1,8 +1,9 @@
 package dan200.computercraft.core.apis.handles;
 
 import com.google.common.io.ByteStreams;
-import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 
 import javax.annotation.Nonnull;
 import java.io.ByteArrayOutputStream;
@@ -35,8 +36,9 @@ public class BinaryInputHandle extends HandleGeneric
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -60,9 +62,9 @@ public class BinaryInputHandle extends HandleGeneric
                             byte[] bytes = new byte[ count ];
                             int read = m_stream.read( bytes );
 
-                            if( read < 0 ) return null;
+                            if( read < 0 ) return MethodResult.empty();
                             if( read < count ) bytes = Arrays.copyOf( bytes, read );
-                            return new Object[] { bytes };
+                            return MethodResult.of( bytes );
                         }
                         else
                         {
@@ -86,18 +88,18 @@ public class BinaryInputHandle extends HandleGeneric
                                 out.write( buffer, 0, read );
                             }
 
-                            return new Object[] { out.toByteArray() };
+                            return MethodResult.of( new Object[]{ out.toByteArray() } );
                         }
                     }
                     else
                     {
                         int b = m_stream.read();
-                        return b == -1 ? null : new Object[] { b };
+                        return b == -1 ? MethodResult.empty() : MethodResult.of( b );
                     }
                 }
                 catch( IOException e )
                 {
-                    return null;
+                    return MethodResult.empty();
                 }
             case 1:
                 // readAll
@@ -105,18 +107,18 @@ public class BinaryInputHandle extends HandleGeneric
                 try
                 {
                     byte[] out = ByteStreams.toByteArray( m_stream );
-                    return out == null ? null : new Object[] { out };
+                    return out == null ? MethodResult.empty() : MethodResult.of( out );
                 }
                 catch( IOException e )
                 {
-                    return null;
+                    return MethodResult.empty();
                 }
             case 2:
                 //close
                 close();
-                return null;
+                return MethodResult.empty();
             default:
-                return null;
+                return MethodResult.empty();
         }
     }
 }

src/main/java/dan200/computercraft/core/apis/handles/BinaryOutputHandle.java

@@ -1,7 +1,8 @@
 package dan200.computercraft.core.apis.handles;
 
-import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.core.apis.ArgumentHelper;
 import dan200.computercraft.shared.util.StringUtil;
 
@@ -30,8 +31,9 @@ public class BinaryOutputHandle extends HandleGeneric
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -54,7 +56,7 @@ public class BinaryOutputHandle extends HandleGeneric
                     {
                         throw ArgumentHelper.badArgument( 0, "string or number", args.length > 0 ? args[ 0 ] : null );
                     }
-                    return null;
+                    return MethodResult.empty();
                 }
                 catch( IOException e )
                 {
@@ -66,18 +68,18 @@ public class BinaryOutputHandle extends HandleGeneric
                 try
                 {
                     m_writer.flush();
-                    return null;
+                    return MethodResult.empty();
                 }
                 catch( IOException e )
                 {
-                    return null;
+                    return MethodResult.empty();
                 }
             case 2:
                 //close
                 close();
-                return null;
+                return MethodResult.empty();
             default:
-                return null;
+                return MethodResult.empty();
         }
     }
 }

src/main/java/dan200/computercraft/core/apis/handles/EncodedInputHandle.java

@@ -1,7 +1,8 @@
 package dan200.computercraft.core.apis.handles;
 
-import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 
 import javax.annotation.Nonnull;
 import java.io.*;
@@ -57,8 +58,9 @@ public class EncodedInputHandle extends HandleGeneric
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -70,16 +72,16 @@ public class EncodedInputHandle extends HandleGeneric
                     String line = m_reader.readLine();
                     if( line != null )
                     {
-                        return new Object[] { line };
+                        return MethodResult.of( line );
                     }
                     else
                     {
-                        return null;
+                        return MethodResult.empty();
                     }
                 }
                 catch( IOException e )
                 {
-                    return null;
+                    return MethodResult.empty();
                 }
             case 1:
                 // readAll
@@ -97,16 +99,16 @@ public class EncodedInputHandle extends HandleGeneric
                             result.append( "\n" );
                         }
                     }
-                    return new Object[] { result.toString() };
+                    return MethodResult.of( result.toString() );
                 }
                 catch( IOException e )
                 {
-                    return null;
+                    return MethodResult.empty();
                 }
             case 2:
                 // close
                 close();
-                return null;
+                return MethodResult.empty();
             case 3:
                 // read
                 checkOpen();
@@ -125,7 +127,7 @@ public class EncodedInputHandle extends HandleGeneric
                         char[] chars = new char[ count ];
                         int read = m_reader.read( chars );
 
-                        return read < 0 ? null : new Object[] { new String( chars, 0, read ) };
+                        return read < 0 ? MethodResult.empty() : MethodResult.of( new String( chars, 0, read ) );
                     }
                     else
                     {
@@ -150,15 +152,15 @@ public class EncodedInputHandle extends HandleGeneric
                             out.append( buffer, 0, read );
                         }
 
-                        return new Object[] { out.toString() };
+                        return MethodResult.of( out.toString() );
                     }
                 }
                 catch( IOException e )
                 {
-                    return null;
+                    return MethodResult.empty();
                 }
             default:
-                return null;
+                return MethodResult.empty();
         }
     }
 }

src/main/java/dan200/computercraft/core/apis/handles/EncodedOutputHandle.java

@@ -1,7 +1,8 @@
 package dan200.computercraft.core.apis.handles;
 
-import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 
 import javax.annotation.Nonnull;
 import java.io.*;
@@ -53,8 +54,9 @@ public class EncodedOutputHandle extends HandleGeneric
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -74,7 +76,7 @@ public class EncodedOutputHandle extends HandleGeneric
                 try
                 {
                     m_writer.write( text, 0, text.length() );
-                    return null;
+                    return MethodResult.empty();
                 }
                 catch( IOException e )
                 {
@@ -98,7 +100,7 @@ public class EncodedOutputHandle extends HandleGeneric
                 {
                     m_writer.write( text, 0, text.length() );
                     m_writer.newLine();
-                    return null;
+                    return MethodResult.empty();
                 }
                 catch( IOException e )
                 {
@@ -111,18 +113,18 @@ public class EncodedOutputHandle extends HandleGeneric
                 try
                 {
                     m_writer.flush();
-                    return null;
+                    return MethodResult.empty();
                 }
                 catch( IOException e )
                 {
-                    return null;
+                    return MethodResult.empty();
                 }
             case 3:
                 // close
                 close();
-                return null;
+                return MethodResult.empty();
             default:
-                return null;
+                return MethodResult.empty();
         }
     }
 }

src/main/java/dan200/computercraft/core/apis/handles/HandleGeneric.java

@@ -1,8 +1,12 @@
 package dan200.computercraft.core.apis.handles;
 
+import dan200.computercraft.api.lua.ICallContext;
+import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.ILuaObject;
 import dan200.computercraft.api.lua.LuaException;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.io.Closeable;
 import java.io.IOException;
 
@@ -32,4 +36,12 @@ public abstract class HandleGeneric implements ILuaObject
         {
         }
     }
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
 }

src/main/java/dan200/computercraft/core/apis/http/HTTPRequest.java

@@ -9,15 +9,14 @@ package dan200.computercraft.core.apis.http;
 import com.google.common.base.Joiner;
 import com.google.common.io.ByteStreams;
 import dan200.computercraft.ComputerCraft;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.ILuaObject;
-import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.core.apis.IAPIEnvironment;
 import dan200.computercraft.core.apis.handles.BinaryInputHandle;
 import dan200.computercraft.core.apis.handles.EncodedInputHandle;
 import dan200.computercraft.core.tracking.TrackingField;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.io.*;
 import java.net.*;
 import java.util.Arrays;
@@ -236,8 +235,9 @@ public class HTTPRequest implements Runnable
                 return newMethods;
             }
 
+            @Nonnull
             @Override
-            public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException, InterruptedException
+            public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
             {
                 if( method < methodOffset )
                 {
@@ -248,19 +248,27 @@ public class HTTPRequest implements Runnable
                     case 0:
                     {
                         // getResponseCode
-                        return new Object[]{ responseCode };
+                        return MethodResult.of( responseCode );
                     }
                     case 1:
                     {
                         // getResponseHeaders
-                        return new Object[]{ responseHeaders };
+                        return MethodResult.of( responseHeaders );
                     }
                     default:
                     {
-                        return null;
+                        return MethodResult.empty();
                     }
                 }
             }
+
+            @Nullable
+            @Override
+            @Deprecated
+            public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+            {
+                return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+            }
         };
     }
 

src/main/java/dan200/computercraft/core/apis/http/WebsocketConnection.java

@@ -7,9 +7,7 @@
 package dan200.computercraft.core.apis.http;
 
 import com.google.common.base.Objects;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.ILuaObject;
-import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.core.apis.HTTPAPI;
 import dan200.computercraft.core.apis.IAPIEnvironment;
 import dan200.computercraft.core.tracking.TrackingField;
@@ -156,33 +154,48 @@ public class WebsocketConnection extends SimpleChannelInboundHandler<Object> imp
 
     @Nullable
     @Override
+    @Deprecated
     public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
+    @Nonnull
+    @Override
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
     {
         switch( method )
         {
             case 0:
-                while( true )
+                checkOpen();
+                return MethodResult.pullEvent( MESSAGE_EVENT, new ILuaFunction()
                 {
-                    checkOpen();
-                    Object[] event = context.pullEvent( MESSAGE_EVENT );
-                    if( event.length >= 3 && Objects.equal( event[1], url ) )
+                    @Nonnull
+                    @Override
+                    public MethodResult call( @Nullable Object[] event ) throws LuaException
                     {
-                        return new Object[]{ event[2] };
+                        if( event != null && event.length >= 3 && Objects.equal( event[1], url ) )
+                        {
+                            return MethodResult.of( event[2] );
+                        }
+
+                        checkOpen();
+                        return MethodResult.pullEvent( MESSAGE_EVENT, this );
                     }
-                }
+                } );
             case 1:
             {
                 checkOpen();
                 String text = arguments.length > 0 && arguments[0] != null ? arguments[0].toString() : "";
                 computer.addTrackingChange( TrackingField.WEBSOCKET_OUTGOING, text.length() );
                 channel.writeAndFlush( new TextWebSocketFrame( text ) );
-                return null;
+                return MethodResult.empty();
             }
             case 2:
                 close( true );
-                return null;
+                return MethodResult.empty();
             default:
-                return null;
+                return MethodResult.empty();
         }
     }
 

src/main/java/dan200/computercraft/core/computer/Computer.java

@@ -265,10 +265,18 @@ public class Computer
 
         @Nullable
         @Override
+        @Deprecated
         public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
         {
             return delegate.callMethod( context, method, arguments );
         }
+
+        @Nonnull
+        @Override
+        public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
+        {
+            return delegate.callMethod( context, method, arguments );
+        }
     }
 
     private static IMount s_romMount = null;
@@ -960,7 +968,7 @@ public class Computer
                 return;
             }
         }
-            
+
         final Computer computer = this;
         ITask task = new ITask() {
             @Override

src/main/java/dan200/computercraft/core/lua/CobaltCallContext.java

@@ -0,0 +1,87 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.lua;
+
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.api.lua.ICallContext;
+import dan200.computercraft.api.lua.ILuaTask;
+import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.core.computer.Computer;
+import dan200.computercraft.core.computer.ITask;
+import dan200.computercraft.core.computer.MainThread;
+
+import javax.annotation.Nonnull;
+
+class CobaltCallContext implements ICallContext
+{
+    private final Computer computer;
+
+    CobaltCallContext( Computer computer )
+    {
+        this.computer = computer;
+    }
+
+    @Override
+    public long issueMainThreadTask( @Nonnull final ILuaTask task ) throws LuaException
+    {
+        // Issue command
+        final long taskID = MainThread.getUniqueTaskID();
+        final ITask iTask = new ITask()
+        {
+            @Override
+            public Computer getOwner()
+            {
+                return computer;
+            }
+
+            @Override
+            public void execute()
+            {
+                try
+                {
+                    Object[] results = task.execute();
+                    if( results != null )
+                    {
+                        Object[] eventArguments = new Object[results.length + 2];
+                        eventArguments[0] = taskID;
+                        eventArguments[1] = true;
+                        System.arraycopy( results, 0, eventArguments, 2, results.length );
+                        computer.queueEvent( "task_complete", eventArguments );
+                    }
+                    else
+                    {
+                        computer.queueEvent( "task_complete", new Object[]{ taskID, true } );
+                    }
+                }
+                catch( LuaException e )
+                {
+                    computer.queueEvent( "task_complete", new Object[]{
+                        taskID, false, e.getMessage()
+                    } );
+                }
+                catch( Throwable t )
+                {
+                    if( ComputerCraft.logPeripheralErrors )
+                    {
+                        ComputerCraft.log.error( "Error running task", t );
+                    }
+                    computer.queueEvent( "task_complete", new Object[]{
+                        taskID, false, "Java Exception Thrown: " + t.toString()
+                    } );
+                }
+            }
+        };
+        if( MainThread.queueTask( iTask ) )
+        {
+            return taskID;
+        }
+        else
+        {
+            throw new LuaException( "Task limit exceeded" );
+        }
+    }
+}

src/main/java/dan200/computercraft/core/lua/CobaltLuaContext.java

@@ -0,0 +1,191 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.lua;
+
+import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.ILuaContextTask;
+import dan200.computercraft.api.lua.ILuaTask;
+import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.core.computer.Computer;
+import org.squiddev.cobalt.LuaError;
+import org.squiddev.cobalt.LuaState;
+import org.squiddev.cobalt.LuaThread;
+import org.squiddev.cobalt.UnwindThrowable;
+
+import javax.annotation.Nonnull;
+import java.lang.ref.WeakReference;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.SynchronousQueue;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * An ugly wrapper for {@link ILuaContext} style calls, which executes them on a separate thread.
+ */
+class CobaltLuaContext extends CobaltCallContext implements ILuaContext
+{
+    private static final ThreadGroup group = new ThreadGroup( "ComputerCraft-Lua" );
+    private static final AtomicInteger threadCounter = new AtomicInteger();
+    private static final ExecutorService threads = new ThreadPoolExecutor(
+        4, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<>(),
+        task -> {
+            Thread thread = new Thread( group, task, group.getName() + "-" + threadCounter.incrementAndGet() );
+            if( !thread.isDaemon() ) thread.setDaemon( true );
+            if( thread.getPriority() != Thread.NORM_PRIORITY ) thread.setPriority( Thread.NORM_PRIORITY );
+            return thread;
+        }
+    );
+
+    private boolean done = false;
+    private Object[] values;
+    private LuaError exception;
+    private final Semaphore yield = new Semaphore();
+    private final Semaphore resume = new Semaphore();
+    private WeakReference<LuaThread> thread;
+
+    CobaltLuaContext( Computer computer, LuaState state )
+    {
+        super( computer );
+        this.thread = state.getCurrentThread().getReference();
+    }
+
+    @Nonnull
+    @Override
+    @Deprecated
+    public Object[] pullEvent( String filter ) throws LuaException, InterruptedException
+    {
+        Object[] results = pullEventRaw( filter );
+        if( results.length >= 1 && results[0].equals( "terminate" ) )
+        {
+            throw new LuaException( "Terminated", 0 );
+        }
+        return results;
+    }
+
+    @Nonnull
+    @Override
+    @Deprecated
+    public Object[] pullEventRaw( String filter ) throws InterruptedException
+    {
+        return yield( new Object[]{ filter } );
+    }
+
+    @Nonnull
+    @Override
+    @Deprecated
+    public Object[] yield( Object[] yieldArgs ) throws InterruptedException
+    {
+        if( done ) throw new IllegalStateException( "Cannot yield when complete" );
+
+        values = yieldArgs;
+        yield.signal();
+
+        // Every 30 seconds check to see if the coroutine has been GCed
+        // if so then abort this task.
+        while( !resume.await( 30000 ) )
+        {
+            if( thread.get() == null ) throw new InterruptedException( "Orphaned async task" );
+        }
+
+        return values;
+    }
+
+    @Override
+    @Deprecated
+    public Object[] executeMainThreadTask( @Nonnull final ILuaTask task ) throws LuaException, InterruptedException
+    {
+        // Issue task
+        final long taskID = issueMainThreadTask( task );
+
+        // Wait for response
+        while( true )
+        {
+            Object[] response = pullEvent( "task_complete" );
+            if( response.length >= 3 && response[1] instanceof Number && response[2] instanceof Boolean )
+            {
+                if( ((Number) response[1]).intValue() == taskID )
+                {
+                    Object[] returnValues = new Object[response.length - 3];
+                    if( (Boolean) response[2] )
+                    {
+                        // Extract the return values from the event and return them
+                        System.arraycopy( response, 3, returnValues, 0, returnValues.length );
+                        return returnValues;
+                    }
+                    else
+                    {
+                        // Extract the error message from the event and raise it
+                        if( response.length >= 4 && response[3] instanceof String )
+                        {
+                            throw new LuaException( (String) response[3] );
+                        }
+                        else
+                        {
+                            throw new LuaException();
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    void execute( ILuaContextTask task )
+    {
+        threads.submit( () -> {
+            try
+            {
+                values = task.execute( this );
+            }
+            catch( LuaException e )
+            {
+                exception = new LuaError( e.getMessage(), e.getLevel() );
+            }
+            catch( InterruptedException e )
+            {
+                exception = new LuaError( "Java Exception Thrown: " + e.toString(), 0 );
+            }
+            finally
+            {
+                done = true;
+                yield.signal();
+            }
+        } );
+    }
+
+    void resume( Object[] args )
+    {
+        values = args;
+        resume.signal();
+    }
+
+    Object[] await( LuaState state, CobaltLuaMachine machine ) throws LuaError, UnwindThrowable
+    {
+        if( !done )
+        {
+            try
+            {
+                yield.await();
+            }
+            catch( InterruptedException e )
+            {
+                throw new LuaError( "Java Exception Thrown: " + e.toString(), 0 );
+            }
+        }
+
+        if( done )
+        {
+            if( exception != null ) throw exception;
+            return values;
+        }
+        else
+        {
+            LuaThread.yield( state, machine.toValues( values ) );
+            throw new IllegalStateException( "Unreachable" );
+        }
+    }
+}

src/main/java/dan200/computercraft/core/lua/CobaltLuaMachine.java

@@ -7,14 +7,9 @@
 package dan200.computercraft.core.lua;
 
 import dan200.computercraft.ComputerCraft;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.ILuaObject;
-import dan200.computercraft.api.lua.ILuaTask;
-import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.api.lua.ILuaAPI;
+import dan200.computercraft.api.lua.ILuaObject;
 import dan200.computercraft.core.computer.Computer;
-import dan200.computercraft.core.computer.ITask;
-import dan200.computercraft.core.computer.MainThread;
 import org.squiddev.cobalt.*;
 import org.squiddev.cobalt.compiler.CompileException;
 import org.squiddev.cobalt.compiler.LoadState;
@@ -27,7 +22,6 @@ import org.squiddev.cobalt.function.VarArgFunction;
 import org.squiddev.cobalt.lib.*;
 import org.squiddev.cobalt.lib.platform.AbstractResourceManipulator;
 
-import javax.annotation.Nonnull;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -76,7 +70,7 @@ public class CobaltLuaMachine implements ILuaMachine
                 int count = ++this.count;
                 if( count > 100000 )
                 {
-                    if( m_hardAbortMessage != null ) LuaThread.yield( state, NONE );
+                    if( m_hardAbortMessage != null ) throw new LuaError( m_hardAbortMessage );
                     this.count = 0;
                 }
                 else
@@ -90,7 +84,7 @@ public class CobaltLuaMachine implements ILuaMachine
             @Override
             public void poll() throws LuaError
             {
-                if( m_hardAbortMessage != null ) LuaThread.yield( state, NONE );
+                if( m_hardAbortMessage != null ) throw new LuaError( m_hardAbortMessage );
                 handleSoftAbort();
             }
 
@@ -125,7 +119,7 @@ public class CobaltLuaMachine implements ILuaMachine
         if( ComputerCraft.debug_enable ) m_globals.load( state, new DebugLib() );
 
         // Register custom load/loadstring provider which automatically adds prefixes.
-        LibFunction.bind( state, m_globals, PrefixLoader.class, new String[]{ "load", "loadstring" } );
+        LibFunction.bind( m_globals, PrefixLoader.class, new String[]{ "load", "loadstring" } );
 
         // Remove globals we don't want to expose
         m_globals.rawset( "collectgarbage", Constants.NIL );
@@ -216,18 +210,13 @@ public class CobaltLuaMachine implements ILuaMachine
                 resumeArgs = varargsOf( valueOf( eventName ), toValues( arguments ) );
             }
 
-            Varargs results = m_mainRoutine.resume( resumeArgs );
+            LuaValue filter = LuaThread.run( m_mainRoutine, resumeArgs ).first();
             if( m_hardAbortMessage != null )
             {
                 throw new LuaError( m_hardAbortMessage );
             }
-            else if( !results.first().checkBoolean() )
-            {
-                throw new LuaError( results.arg( 2 ).checkString() );
-            }
             else
             {
-                LuaValue filter = results.arg( 2 );
                 if( filter.isString() )
                 {
                     m_eventFilter = filter.toString();
@@ -246,6 +235,7 @@ public class CobaltLuaMachine implements ILuaMachine
         }
         catch( LuaError e )
         {
+            if( ComputerCraft.logPeripheralErrors ) ComputerCraft.log.error( "Main thread crashed", e );
             m_mainRoutine.abandon();
             m_mainRoutine = null;
         }
@@ -302,181 +292,12 @@ public class CobaltLuaMachine implements ILuaMachine
     {
         LuaTable table = new LuaTable();
         String[] methods = object.getMethodNames();
-        for( int i = 0; i < methods.length; ++i )
+        for( int method = 0; method < methods.length; method++ )
         {
-            if( methods[ i ] != null )
+            if( methods[method] != null )
             {
-                final int method = i;
-                final ILuaObject apiObject = object;
-                final String methodName = methods[ i ];
-                table.rawset( methodName, new VarArgFunction()
-                {
-                    @Override
-                    public Varargs invoke( final LuaState state, Varargs _args ) throws LuaError
-                    {
-                        Object[] arguments = toObjects( _args, 1 );
-                        Object[] results;
-                        try
-                        {
-                            results = apiObject.callMethod( new ILuaContext()
-                            {
-                                @Nonnull
-                                @Override
-                                public Object[] pullEvent( String filter ) throws LuaException, InterruptedException
-                                {
-                                    Object[] results = pullEventRaw( filter );
-                                    if( results.length >= 1 && results[ 0 ].equals( "terminate" ) )
-                                    {
-                                        throw new LuaException( "Terminated", 0 );
-                                    }
-                                    return results;
-                                }
-
-                                @Nonnull
-                                @Override
-                                public Object[] pullEventRaw( String filter ) throws InterruptedException
-                                {
-                                    return yield( new Object[] { filter } );
-                                }
-
-                                @Nonnull
-                                @Override
-                                public Object[] yield( Object[] yieldArgs ) throws InterruptedException
-                                {
-                                    try
-                                    {
-                                        Varargs results = LuaThread.yield( state, toValues( yieldArgs ) );
-                                        return toObjects( results, 1 );
-                                    }
-                                    catch( OrphanedThread e )
-                                    {
-                                        throw new InterruptedException();
-                                    }
-                                    catch( Throwable e )
-                                    {
-                                        throw new RuntimeException( e );
-                                    }
-                                }
-
-                                @Override
-                                public long issueMainThreadTask( @Nonnull final ILuaTask task ) throws LuaException
-                                {
-                                    // Issue command
-                                    final long taskID = MainThread.getUniqueTaskID();
-                                    final ITask iTask = new ITask()
-                                    {
-                                        @Override
-                                        public Computer getOwner()
-                                        {
-                                            return m_computer;
-                                        }
-
-                                        @Override
-                                        public void execute()
-                                        {
-                                            try
-                                            {
-                                                Object[] results = task.execute();
-                                                if( results != null )
-                                                {
-                                                    Object[] eventArguments = new Object[ results.length + 2 ];
-                                                    eventArguments[ 0 ] = taskID;
-                                                    eventArguments[ 1 ] = true;
-                                                    System.arraycopy( results, 0, eventArguments, 2, results.length );
-                                                    m_computer.queueEvent( "task_complete", eventArguments );
-                                                }
-                                                else
-                                                {
-                                                    m_computer.queueEvent( "task_complete", new Object[] { taskID, true } );
-                                                }
-                                            }
-                                            catch( LuaException e )
-                                            {
-                                                m_computer.queueEvent( "task_complete", new Object[] {
-                                                    taskID, false, e.getMessage()
-                                                } );
-                                            }
-                                            catch( Throwable t )
-                                            {
-                                                if( ComputerCraft.logPeripheralErrors )
-                                                {
-                                                    ComputerCraft.log.error( "Error running task", t );
-                                                }
-                                                m_computer.queueEvent( "task_complete", new Object[] {
-                                                    taskID, false, "Java Exception Thrown: " + t.toString()
-                                                } );
-                                            }
-                                        }
-                                    };
-                                    if( MainThread.queueTask( iTask ) )
-                                    {
-                                        return taskID;
-                                    }
-                                    else
-                                    {
-                                        throw new LuaException( "Task limit exceeded" );
-                                    }
-                                }
-
-                                @Override
-                                public Object[] executeMainThreadTask( @Nonnull final ILuaTask task ) throws LuaException, InterruptedException
-                                {
-                                    // Issue task
-                                    final long taskID = issueMainThreadTask( task );
-
-                                    // Wait for response
-                                    while( true )
-                                    {
-                                        Object[] response = pullEvent( "task_complete" );
-                                        if( response.length >= 3 && response[ 1 ] instanceof Number && response[ 2 ] instanceof Boolean )
-                                        {
-                                            if( ((Number) response[ 1 ]).intValue() == taskID )
-                                            {
-                                                Object[] returnValues = new Object[ response.length - 3 ];
-                                                if( (Boolean) response[ 2 ] )
-                                                {
-                                                    // Extract the return values from the event and return them
-                                                    System.arraycopy( response, 3, returnValues, 0, returnValues.length );
-                                                    return returnValues;
-                                                }
-                                                else
-                                                {
-                                                    // Extract the error message from the event and raise it
-                                                    if( response.length >= 4 && response[ 3 ] instanceof String )
-                                                    {
-                                                        throw new LuaException( (String) response[ 3 ] );
-                                                    }
-                                                    else
-                                                    {
-                                                        throw new LuaException();
-                                                    }
-                                                }
-                                            }
-                                        }
-                                    }
-
-                                }
-                            }, method, arguments );
-                        }
-                        catch( InterruptedException e )
-                        {
-                            throw new OrphanedThread();
-                        }
-                        catch( LuaException e )
-                        {
-                            throw new LuaError( e.getMessage(), e.getLevel() );
-                        }
-                        catch( Throwable t )
-                        {
-                            if( ComputerCraft.logPeripheralErrors )
-                            {
-                                ComputerCraft.log.error( "Error calling " + methodName + " on " + apiObject, t );
-                            }
-                            throw new LuaError( "Java Exception Thrown: " + t.toString(), 0 );
-                        }
-                        return toValues( results );
-                    }
-                } );
+                final String methodName = methods[method];
+                table.rawset( methodName, new CobaltWrapperFunction( this, m_computer, object, method, methodName ) );
             }
         }
         return table;
@@ -544,7 +365,7 @@ public class CobaltLuaMachine implements ILuaMachine
         }
     }
 
-    private Varargs toValues( Object[] objects )
+    Varargs toValues( Object[] objects )
     {
         if( objects == null || objects.length == 0 )
         {
@@ -635,7 +456,7 @@ public class CobaltLuaMachine implements ILuaMachine
         }
     }
 
-    private static Object[] toObjects( Varargs values, int startIdx )
+    static Object[] toObjects( Varargs values, int startIdx )
     {
         int count = values.count();
         Object[] objects = new Object[ count - startIdx + 1 ];
@@ -703,13 +524,23 @@ public class CobaltLuaMachine implements ILuaMachine
             if( remaining <= 0 )
             {
                 LuaValue s;
+                state.getCurrentThread().disableYield();
                 try
                 {
                     s = OperationHelper.call( state, func );
-                } catch (LuaError e)
+                }
+                catch( UnwindThrowable e )
+                {
+                    throw new IOException( "Impossible yield within load" );
+                }
+                catch( LuaError e )
                 {
                     throw new IOException( e );
                 }
+                finally
+                {
+                    state.getCurrentThread().enableYield();
+                }
 
                 if( s.isNil() )
                 {
@@ -735,4 +566,5 @@ public class CobaltLuaMachine implements ILuaMachine
             return bytes[offset++];
         }
     }
+
 }

src/main/java/dan200/computercraft/core/lua/CobaltWrapperFunction.java

@@ -0,0 +1,292 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.lua;
+
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.api.lua.ILuaFunction;
+import dan200.computercraft.api.lua.ILuaObject;
+import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
+import dan200.computercraft.core.computer.Computer;
+import org.squiddev.cobalt.*;
+import org.squiddev.cobalt.debug.DebugState;
+import org.squiddev.cobalt.function.VarArgFunction;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+class CobaltWrapperFunction extends VarArgFunction implements Resumable<CobaltWrapperFunction.State>
+{
+    private final CobaltLuaMachine machine;
+    private final Computer computer;
+    private final CobaltCallContext callContext;
+
+    private final ILuaObject delegate;
+    private final int method;
+    private final String methodName;
+
+    CobaltWrapperFunction( CobaltLuaMachine machine, Computer computer, ILuaObject delegate, int method, String methodName )
+    {
+        this.machine = machine;
+        this.computer = computer;
+        this.callContext = new CobaltCallContext( computer );
+        this.delegate = delegate;
+        this.method = method;
+        this.methodName = methodName;
+    }
+
+    @Override
+    public Varargs invoke( final LuaState state, Varargs args ) throws LuaError, UnwindThrowable
+    {
+        MethodResult future;
+        try
+        {
+            future = delegate.callMethod( callContext, method, CobaltLuaMachine.toObjects( args, 1 ) );
+        }
+        catch( LuaException e )
+        {
+            throw new LuaError( e.getMessage(), e.getLevel() );
+        }
+        catch( Exception e )
+        {
+            if( ComputerCraft.logPeripheralErrors )
+            {
+                ComputerCraft.log.error( "Error calling " + methodName + " on " + delegate, e );
+            }
+            throw new LuaError( "Java Exception Thrown: " + e.toString(), 0 );
+        }
+
+        // Verify we've a "well formed" future
+        if( future == null )
+        {
+            ComputerCraft.log.error( "Null result from " + delegate );
+            throw new LuaError( "Java Exception Thrown: Null result" );
+        }
+
+        // Fast path for immediate results
+        if( future instanceof MethodResult.Immediate )
+        {
+            return machine.toValues( ((MethodResult.Immediate) future).getResult() );
+        }
+
+        State context = new State();
+        try
+        {
+            return runFuture( state, context, future );
+        }
+        catch( UnwindThrowable e )
+        {
+            // Push our state onto the stack if need-be. Normally this wouldn't be safe and we 
+            // should do this at the very beginning, but we know that we won't be calling anything 
+            // else which will push to the resume stack.
+            DebugState ds = state.debug.getDebugState();
+            state.debug.onCall( ds, this, context );
+            throw e;
+        }
+    }
+
+    @Override
+    public Varargs resume( LuaState state, State context, Varargs args ) throws LuaError, UnwindThrowable
+    {
+        Varargs result;
+        try
+        {
+            result = doResume( state, context, args );
+        }
+        catch( LuaError e )
+        {
+            state.debug.onReturn();
+            throw e;
+        }
+        catch( Exception e )
+        {
+            state.debug.onReturn();
+            throw new LuaError( e );
+        }
+
+        state.debug.onReturn();
+        return result;
+    }
+
+    private Varargs doResume( LuaState state, State context, Varargs args ) throws LuaError, UnwindThrowable
+    {
+        MethodResult future = context.pending;
+        if( future instanceof MethodResult.OnEvent )
+        {
+            MethodResult.OnEvent onEvent = (MethodResult.OnEvent) future;
+            if( !onEvent.isRaw() && args.first().toString().equals( "terminate" ) )
+            {
+                throw new LuaError( "Terminated", 0 );
+            }
+
+            return runCallback( state, context, CobaltLuaMachine.toObjects( args, 1 ) );
+        }
+        else if( future instanceof MethodResult.OnMainThread )
+        {
+            if( args.arg( 2 ).isNumber() && args.arg( 3 ).isBoolean() && args.arg( 2 ).toLong() == context.taskId )
+            {
+                if( args.arg( 3 ).toBoolean() )
+                {
+                    // Extract the return values from the event and return them
+                    return runFuture( state, context, context.taskResult );
+                }
+                else
+                {
+                    // Extract the error message from the event and raise it
+                    throw new LuaError( args.arg( 4 ) );
+                }
+            }
+            else
+            {
+                LuaThread.yield( state, ValueFactory.valueOf( "task_complete" ) );
+                throw new IllegalStateException( "Unreachable" );
+            }
+        }
+        else if( future instanceof MethodResult.WithLuaContext )
+        {
+            context.luaContext.resume( CobaltLuaMachine.toObjects( args, 1 ) );
+            return runCallback( state, context, context.luaContext.await( state, machine ) );
+        }
+        else
+        {
+            ComputerCraft.log.error( "Unknown method result " + future );
+            throw new LuaError( "Java Exception Thrown: Unknown method result" );
+        }
+    }
+
+    @Override
+    public Varargs resumeError( LuaState state, State context, LuaError error ) throws LuaError
+    {
+        state.debug.onReturn();
+        throw error;
+    }
+
+    private Varargs runFuture( LuaState state, State context, MethodResult future ) throws LuaError, UnwindThrowable
+    {
+        Deque<ILuaFunction> callbacks = context.callbacks;
+        while( true )
+        {
+            if( future instanceof MethodResult.AndThen )
+            {
+                MethodResult.AndThen then = ((MethodResult.AndThen) future);
+
+                // Thens are "unwrapped", being pushed onto a stack
+                if( callbacks == null ) callbacks = context.callbacks = new ArrayDeque<>();
+                callbacks.addLast( then.getCallback() );
+
+                future = then.getPrevious();
+            }
+            else if( future instanceof MethodResult.Immediate )
+            {
+                Object[] values = ((MethodResult.Immediate) future).getResult();
+
+                // Immediate values values will attempt to call the previous "then", or return if nothing 
+                // else needs to be done.
+                ILuaFunction callback = callbacks == null ? null : callbacks.pollLast();
+                if( callback == null ) return machine.toValues( values );
+
+                future = runFunction( callback, values );
+            }
+            else if( future instanceof MethodResult.OnEvent )
+            {
+                MethodResult.OnEvent onEvent = (MethodResult.OnEvent) future;
+
+                // Mark this future as pending and yield
+                context.pending = future;
+                String filter = onEvent.getFilter();
+                LuaThread.yield( state, filter == null ? Constants.NIL : ValueFactory.valueOf( filter ) );
+                throw new IllegalStateException( "Unreachable" );
+            }
+            else if( future instanceof MethodResult.OnMainThread )
+            {
+                MethodResult.OnMainThread onMainThread = (MethodResult.OnMainThread) future;
+
+                // Mark this future as pending and yield
+                context.pending = future;
+                try
+                {
+                    context.taskId = callContext.issueMainThreadTask( () -> {
+                        context.taskResult = onMainThread.getTask().execute();
+                        return null;
+                    } );
+                }
+                catch( LuaException e )
+                {
+                    throw new LuaError( e.getMessage(), e.getLevel() );
+                }
+
+                LuaThread.yield( state, ValueFactory.valueOf( "task_complete" ) );
+                throw new IllegalStateException( "Unreachable" );
+            }
+            else if( future instanceof MethodResult.WithLuaContext )
+            {
+                MethodResult.WithLuaContext withContext = (MethodResult.WithLuaContext) future;
+
+                // Mark this future as pending and execute on a separate thread.
+                context.pending = future;
+                CobaltLuaContext luaContext = context.luaContext = new CobaltLuaContext( computer, state );
+                luaContext.execute( withContext.getConsumer() );
+                return runCallback( state, context, luaContext.await( state, machine ) );
+            }
+            else
+            {
+                ComputerCraft.log.error( "Unknown method result " + future );
+                throw new LuaError( "Java Exception Thrown: Unknown method result" );
+            }
+        }
+    }
+
+    private Varargs runCallback( LuaState state, State context, Object[] args ) throws LuaError, UnwindThrowable
+    {
+        Deque<ILuaFunction> callbacks = context.callbacks;
+        ILuaFunction callback = callbacks == null ? null : callbacks.pollLast();
+        if( callback == null ) return machine.toValues( args );
+
+        return runFuture( state, context, runFunction( callback, args ) );
+    }
+
+    private MethodResult runFunction( ILuaFunction func, Object[] args ) throws LuaError
+    {
+        MethodResult result;
+        try
+        {
+            result = func.call( args );
+        }
+        catch( LuaException e )
+        {
+            throw new LuaError( e.getMessage(), e.getLevel() );
+        }
+        catch( Exception e )
+        {
+            if( ComputerCraft.logPeripheralErrors )
+            {
+                ComputerCraft.log.error( "Error calling " + methodName + " on " + delegate, e );
+            }
+            throw new LuaError( "Java Exception Thrown: " + e.toString(), 0 );
+        }
+
+        if( result == null )
+        {
+            ComputerCraft.log.error( "Null result from " + func );
+            throw new LuaError( "Java Exception Thrown: Null result" );
+        }
+
+        return result;
+    }
+
+    static class State
+    {
+        Deque<ILuaFunction> callbacks;
+
+        MethodResult pending;
+
+        CobaltLuaContext luaContext;
+
+        long taskId;
+        MethodResult taskResult;
+    }
+}

src/main/java/dan200/computercraft/core/lua/Semaphore.java

@@ -0,0 +1,38 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.lua;
+
+/**
+ * A trivial way of signalling
+ */
+public final class Semaphore
+{
+    private volatile boolean state = false;
+
+    public synchronized void signal()
+    {
+        state = true;
+        notify();
+    }
+
+    public synchronized void await() throws InterruptedException
+    {
+        while( !state ) wait();
+        state = false;
+    }
+
+    public synchronized boolean await( long timeout ) throws InterruptedException
+    {
+        if( !state )
+        {
+            wait( timeout );
+            if( !state ) return false;
+        }
+        state = false;
+        return true;
+    }
+}

src/main/java/dan200/computercraft/shared/computer/apis/CommandAPI.java

@@ -8,9 +8,7 @@ package dan200.computercraft.shared.computer.apis;
 
 import com.google.common.collect.ImmutableMap;
 import dan200.computercraft.ComputerCraft;
-import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.shared.computer.blocks.TileCommandComputer;
 import dan200.computercraft.shared.util.WorldUtil;
 import net.minecraft.block.Block;
@@ -24,6 +22,7 @@ import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -82,7 +81,7 @@ public class CommandAPI implements ILuaAPI
                 sender.clearOutput();
 
                 int result = commandManager.executeCommand( sender, command );
-                return new Object[]{ (result > 0), sender.copyOutput() };
+                return new Object[] { (result > 0), sender.copyOutput() };
             }
             catch( Throwable t )
             {
@@ -90,7 +89,7 @@ public class CommandAPI implements ILuaAPI
                 {
                     ComputerCraft.log.error( "Error running command.", t );
                 }
-                return new Object[]{ false, createOutput( "Java Exception Thrown: " + t.toString() ) };
+                return new Object[] { false, createOutput( "Java Exception Thrown: " + t.toString() ) };
             }
         }
         else
@@ -131,7 +130,8 @@ public class CommandAPI implements ILuaAPI
     }
 
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    @Nonnull
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
     {
         switch( method )
         {
@@ -139,19 +139,19 @@ public class CommandAPI implements ILuaAPI
             {
                 // exec
                 final String command = getString( arguments, 0 );
-                return context.executeMainThreadTask( () -> doCommand( command ) );
+                return MethodResult.onMainThread( () -> MethodResult.of( doCommand( command ) ) );
             }
             case 1:
             {
                 // execAsync
                 final String command = getString( arguments, 0 );
                 long taskID = context.issueMainThreadTask( () -> doCommand( command ) );
-                return new Object[] { taskID };
+                return MethodResult.of( taskID );
             }
             case 2:
             {
                 // list
-                return context.executeMainThreadTask( () ->
+                return MethodResult.onMainThread( () ->
                 {
                     int i = 1;
                     Map<Object, Object> result = new HashMap<>();
@@ -182,7 +182,7 @@ public class CommandAPI implements ILuaAPI
                             }
                         }
                     }
-                    return new Object[]{ result };
+                    return MethodResult.of( result );
                 } );
             }
             case 3:
@@ -190,7 +190,7 @@ public class CommandAPI implements ILuaAPI
                 // getBlockPosition
                 // This is probably safe to do on the Lua thread. Probably.
                 BlockPos pos = m_computer.getPos();
-                return new Object[] { pos.getX(), pos.getY(), pos.getZ() };
+                return MethodResult.of( pos.getX(), pos.getY(), pos.getZ() );
             }
             case 4:
             {
@@ -201,7 +201,7 @@ public class CommandAPI implements ILuaAPI
                 final int maxx = getInt( arguments, 3 );
                 final int maxy = getInt( arguments, 4 );
                 final int maxz = getInt( arguments, 5 );
-                return context.executeMainThreadTask( () ->
+                return MethodResult.onMainThread( () ->
                 {
                     // Get the details of the block
                     World world = m_computer.getWorld();
@@ -236,7 +236,7 @@ public class CommandAPI implements ILuaAPI
                             }
                         }
                     }
-                    return new Object[]{ results };
+                    return MethodResult.of( results );
                 } );
             }
             case 5:
@@ -245,14 +245,14 @@ public class CommandAPI implements ILuaAPI
                 final int x = getInt( arguments, 0 );
                 final int y = getInt( arguments, 1 );
                 final int z = getInt( arguments, 2 );
-                return context.executeMainThreadTask( () ->
+                return MethodResult.onMainThread( () ->
                 {
                     // Get the details of the block
                     World world = m_computer.getWorld();
                     BlockPos position = new BlockPos( x, y, z );
                     if( WorldUtil.isBlockInWorld( world, position ) )
                     {
-                        return new Object[]{ getBlockInfo( world, position ) };
+                        return MethodResult.of( getBlockInfo( world, position ) );
                     }
                     else
                     {
@@ -262,8 +262,16 @@ public class CommandAPI implements ILuaAPI
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
 }

src/main/java/dan200/computercraft/shared/computer/blocks/ComputerPeripheral.java

@@ -6,11 +6,15 @@
 
 package dan200.computercraft.shared.computer.blocks;
 
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 public class ComputerPeripheral
     implements IPeripheral
@@ -23,7 +27,7 @@ public class ComputerPeripheral
         m_type = type;
         m_computer = computer;
     }
-        
+
     // IPeripheral implementation
 
     @Nonnull
@@ -47,8 +51,9 @@ public class ComputerPeripheral
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments )
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object[] arguments )
     {
         switch( method )
         {
@@ -56,42 +61,48 @@ public class ComputerPeripheral
             {
                 // turnOn
                 m_computer.turnOn();
-                return null;
+                return MethodResult.empty();
             }
             case 1:
             {
                 // shutdown
                 m_computer.shutdown();
-                return null;
+                return MethodResult.empty();
             }
             case 2:
             {
                 // reboot
                 m_computer.reboot();
-                return null;
+                return MethodResult.empty();
             }
             case 3:
             {
                 // getID
-                return new Object[] {
-                    m_computer.assignID()
-                };
+                return MethodResult.of( m_computer.assignID() );
             }
             case 4:
             {
                 // isOn
-                return new Object[] { m_computer.isOn() };
+                return MethodResult.of( m_computer.isOn() );
             }
             case 5:
                 // getLabel
-                return new Object[] { m_computer.getLabel() };
+                return MethodResult.of( m_computer.getLabel() );
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
 
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull IComputerAccess access, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( access, (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
     @Override
     public boolean equals( IPeripheral other )
     {

src/main/java/dan200/computercraft/shared/peripheral/commandblock/CommandBlockPeripheral.java

@@ -6,14 +6,17 @@
 
 package dan200.computercraft.shared.peripheral.commandblock;
 
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import net.minecraft.tileentity.TileEntityCommandBlock;
 import net.minecraft.util.math.BlockPos;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.getString;
 
@@ -46,17 +49,18 @@ public class CommandBlockPeripheral implements IPeripheral
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull final Object[] arguments ) throws LuaException, InterruptedException
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull final Object[] arguments ) throws LuaException
     {
-        switch (method)
+        switch( method )
         {
             case 0:
             {
                 // getCommand
-                return context.executeMainThreadTask( () -> new Object[] {
-                    m_commandBlock.getCommandBlockLogic().getCommand()
-                } );
+                return MethodResult.onMainThread( () ->
+                    MethodResult.of( m_commandBlock.getCommandBlockLogic().getCommand() )
+                );
             }
             case 1:
             {
@@ -69,27 +73,35 @@ public class CommandBlockPeripheral implements IPeripheral
                     m_commandBlock.getWorld().markBlockRangeForRenderUpdate( pos, pos );
                     return null;
                 } );
-                return null;
+                return MethodResult.empty();
             }
             case 2:
             {
                 // runCommand
-                return context.executeMainThreadTask( () ->
+                return MethodResult.onMainThread( () ->
                 {
                     m_commandBlock.getCommandBlockLogic().trigger( m_commandBlock.getWorld() );
                     int result = m_commandBlock.getCommandBlockLogic().getSuccessCount();
                     if( result > 0 )
                     {
-                        return new Object[] { true };
+                        return MethodResult.of( true );
                     }
                     else
                     {
-                        return new Object[] { false, "Command failed" };
+                        return MethodResult.of( false, "Command failed" );
                     }
                 } );
             }
         }
-        return null;
+        return MethodResult.empty();
+    }
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull IComputerAccess access, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( access, (ICallContext) context, method, arguments ).evaluate( context );
     }
 
     @Override

src/main/java/dan200/computercraft/shared/peripheral/diskdrive/DiskDrivePeripheral.java

@@ -6,8 +6,10 @@
 
 package dan200.computercraft.shared.peripheral.diskdrive;
 
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.media.IMedia;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
@@ -17,6 +19,7 @@ import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.optString;
 
@@ -55,17 +58,18 @@ public class DiskDrivePeripheral implements IPeripheral
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
     {
         switch( method )
         {
             case 0:
             {
                 // isDiskPresent
-                return new Object[] {
+                return MethodResult.of(
                     !m_diskDrive.getDiskStack().isEmpty()
-                };
+                );
             }
             case 1:
             {
@@ -73,9 +77,9 @@ public class DiskDrivePeripheral implements IPeripheral
                 IMedia media = m_diskDrive.getDiskMedia();
                 if( media != null )
                 {
-                    return new Object[] { media.getLabel( m_diskDrive.getDiskStack() ) };
+                    return MethodResult.of( media.getLabel( m_diskDrive.getDiskStack() ) );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 2:
             {
@@ -96,21 +100,21 @@ public class DiskDrivePeripheral implements IPeripheral
                         throw new LuaException( "Disk label cannot be changed" );
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 3:
             {
                 // hasData
-                return new Object[] {
+                return MethodResult.of(
                     m_diskDrive.getDiskMountPath( computer ) != null
-                };
+                );
             }
             case 4:
             {
                 // getMountPath
-                return new Object[] {
+                return MethodResult.of(
                     m_diskDrive.getDiskMountPath( computer )
-                };
+                );
             }
             case 5:
             {
@@ -118,9 +122,9 @@ public class DiskDrivePeripheral implements IPeripheral
                 IMedia media = m_diskDrive.getDiskMedia();
                 if( media != null )
                 {
-                    return new Object[] { media.getAudio( m_diskDrive.getDiskStack() ) != null };
+                    return MethodResult.of( media.getAudio( m_diskDrive.getDiskStack() ) != null );
                 }
-                return new Object[] { false };
+                return MethodResult.of( false );
             }
             case 6:
             {
@@ -128,27 +132,27 @@ public class DiskDrivePeripheral implements IPeripheral
                 IMedia media = m_diskDrive.getDiskMedia();
                 if( media != null )
                 {
-                    return new Object[] { media.getAudioTitle( m_diskDrive.getDiskStack() ) };
+                    return MethodResult.of( media.getAudioTitle( m_diskDrive.getDiskStack() ) );
                 }
-                return new Object[] { false };
+                return MethodResult.of( false );
             }
             case 7:
             {
                 // playAudio
                 m_diskDrive.playDiskAudio();
-                return null;
+                return MethodResult.empty();
             }
             case 8:
             {
                 // stopAudio
                 m_diskDrive.stopDiskAudio();
-                return null;
+                return MethodResult.empty();
             }
             case 9:
             {
                 // eject
                 m_diskDrive.ejectDisk();
-                return null;
+                return MethodResult.empty();
             }
             case 10:
             {
@@ -159,18 +163,27 @@ public class DiskDrivePeripheral implements IPeripheral
                     Item item = disk.getItem();
                     if( item instanceof ItemDiskLegacy )
                     {
-                        return new Object[] { ((ItemDiskLegacy)item).getDiskID( disk ) };
+                        return MethodResult.of( ((ItemDiskLegacy)item).getDiskID( disk ) );
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
 
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull IComputerAccess access, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( access, (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
+
     @Override
     public void attach( @Nonnull IComputerAccess computer )
     {

src/main/java/dan200/computercraft/shared/peripheral/modem/ModemPeripheral.java

@@ -6,8 +6,10 @@
 
 package dan200.computercraft.shared.peripheral.modem;
 
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.network.IPacketNetwork;
 import dan200.computercraft.api.network.IPacketReceiver;
 import dan200.computercraft.api.network.IPacketSender;
@@ -20,6 +22,7 @@ import net.minecraft.util.math.Vec3d;
 import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.getInt;
 
@@ -157,8 +160,9 @@ public abstract class ModemPeripheral
         return channel;
     }
     
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
     {
         switch( method )
         {
@@ -183,7 +187,7 @@ public abstract class ModemPeripheral
                         }
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 1:
             {
@@ -192,7 +196,7 @@ public abstract class ModemPeripheral
                 synchronized( this )
                 {
                     boolean open = m_channels.contains( channel );
-                    return new Object[] { open };
+                    return MethodResult.of( open );
                 }
             }
             case 2:
@@ -210,7 +214,7 @@ public abstract class ModemPeripheral
                         }
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 3:
             {
@@ -228,7 +232,7 @@ public abstract class ModemPeripheral
                         }
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 4:
             {
@@ -253,7 +257,7 @@ public abstract class ModemPeripheral
                         }
                     }
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 5:
             {
@@ -262,18 +266,26 @@ public abstract class ModemPeripheral
                 {
                     if( m_network != null )
                     {
-                        return new Object[] { m_network.isWireless() };
+                        return MethodResult.of( m_network.isWireless() );
                     }
                 }
-                return new Object[] { false };
+                return MethodResult.of(false);
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
-    
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( computer, (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
     @Override
     public synchronized void attach( @Nonnull IComputerAccess computer )
     {

src/main/java/dan200/computercraft/shared/peripheral/modem/WiredModemPeripheral.java

@@ -3,8 +3,9 @@ package dan200.computercraft.shared.peripheral.modem;
 import com.google.common.collect.ImmutableMap;
 import dan200.computercraft.api.filesystem.IMount;
 import dan200.computercraft.api.filesystem.IWritableMount;
-import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.network.IPacketNetwork;
 import dan200.computercraft.api.network.wired.IWiredNode;
 import dan200.computercraft.api.network.wired.IWiredSender;
@@ -79,8 +80,9 @@ public abstract class WiredModemPeripheral extends ModemPeripheral implements IW
         return newMethods;
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
     {
         String[] methods = super.getMethodNames();
         switch( method - methods.length )
@@ -96,14 +98,14 @@ public abstract class WiredModemPeripheral extends ModemPeripheral implements IW
                     {
                         table.put( idx++, name );
                     }
-                    return new Object[]{ table };
+                    return MethodResult.of( table );
                 }
             }
             case 1:
             {
                 // isPresentRemote
                 String type = getTypeRemote( getString( arguments, 0 ) );
-                return new Object[]{ type != null };
+                return MethodResult.of( type != null );
             }
             case 2:
             {
@@ -111,9 +113,9 @@ public abstract class WiredModemPeripheral extends ModemPeripheral implements IW
                 String type = getTypeRemote( getString( arguments, 0 ) );
                 if( type != null )
                 {
-                    return new Object[]{ type };
+                    return MethodResult.of( type );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 3:
             {
@@ -126,9 +128,9 @@ public abstract class WiredModemPeripheral extends ModemPeripheral implements IW
                     {
                         table.put( i + 1, methodNames[i] );
                     }
-                    return new Object[]{ table };
+                    return MethodResult.of( table );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 4:
             {
@@ -143,7 +145,7 @@ public abstract class WiredModemPeripheral extends ModemPeripheral implements IW
             {
                 // getNameLocal
                 String local = getLocalPeripheral().getConnectedName();
-                return local == null ? null : new Object[]{ local };
+                return local == null ? MethodResult.empty() : MethodResult.of( local );
             }
             default:
             {
@@ -261,7 +263,7 @@ public abstract class WiredModemPeripheral extends ModemPeripheral implements IW
         return null;
     }
 
-    private Object[] callMethodRemote( String remoteName, ILuaContext context, String method, Object[] arguments ) throws LuaException, InterruptedException
+    private MethodResult callMethodRemote( String remoteName, ICallContext context, String method, Object[] arguments ) throws LuaException
     {
         RemotePeripheralWrapper wrapper;
         synchronized( peripheralWrappers )
@@ -330,7 +332,7 @@ public abstract class WiredModemPeripheral extends ModemPeripheral implements IW
             return m_methods;
         }
 
-        public Object[] callMethod( ILuaContext context, String methodName, Object[] arguments ) throws LuaException, InterruptedException
+        public MethodResult callMethod( ICallContext context, String methodName, Object[] arguments ) throws LuaException
         {
             if( m_methodMap.containsKey( methodName ) )
             {

src/main/java/dan200/computercraft/shared/peripheral/monitor/MonitorPeripheral.java

@@ -6,8 +6,10 @@
 
 package dan200.computercraft.shared.peripheral.monitor;
 
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.core.apis.TermAPI;
@@ -16,6 +18,7 @@ import dan200.computercraft.shared.util.Palette;
 import org.apache.commons.lang3.ArrayUtils;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.*;
 
@@ -70,8 +73,9 @@ public class MonitorPeripheral implements IPeripheral
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object args[] ) throws LuaException
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object args[] ) throws LuaException
     {
         ServerMonitor monitor = m_monitor.getCachedServerMonitor();
         if( monitor == null ) throw new LuaException( "Monitor has been detatched" );
@@ -85,21 +89,24 @@ public class MonitorPeripheral implements IPeripheral
             {
                 // write
                 String text;
-                if( args.length > 0 && args[0] != null ) {
-                    text = args[0].toString();
-                } else {
+                if( args.length > 0 && args[ 0 ] != null )
+                {
+                    text = args[ 0 ].toString();
+                }
+                else
+                {
                     text = "";
                 }
                 terminal.write( text );
                 terminal.setCursorPos( terminal.getCursorX() + text.length(), terminal.getCursorY() );
-                return null;
+                return MethodResult.empty();
             }
             case 1:
             {
                 // scroll
                 int value = getInt( args, 0 );
                 terminal.scroll( value );
-                return null;
+                return MethodResult.empty();
             }
             case 2:
             {
@@ -107,42 +114,42 @@ public class MonitorPeripheral implements IPeripheral
                 int x = getInt( args, 0 ) - 1;
                 int y = getInt( args, 1 ) - 1;
                 terminal.setCursorPos( x, y );
-                return null;
+                return MethodResult.empty();
             }
             case 3:
             {
                 // setCursorBlink
                 boolean blink = getBoolean( args, 0 );
                 terminal.setCursorBlink( blink );
-                return null;
+                return MethodResult.empty();
             }
             case 4:
             {
                 // getCursorPos
-                return new Object[] {
+                return MethodResult.of(
                     terminal.getCursorX() + 1,
                     terminal.getCursorY() + 1
-                };
+                );
             }
             case 5:
             {
                 // getSize
-                return new Object[] {
+                return MethodResult.of(
                     terminal.getWidth(),
                     terminal.getHeight()
-                };
+                );
             }
             case 6:
             {
                 // clear
                 terminal.clear();
-                return null;
+                return MethodResult.empty();
             }
             case 7:
             {
                 // clearLine
                 terminal.clearLine();
-                return null;
+                return MethodResult.empty();
             }
             case 8:
             {
@@ -153,7 +160,7 @@ public class MonitorPeripheral implements IPeripheral
                     throw new LuaException( "Expected number in range 0.5-5" );
                 }
                 monitor.setTextScale( scale );
-                return null;
+                return MethodResult.empty();
             }
             case 9:
             case 10:
@@ -161,7 +168,7 @@ public class MonitorPeripheral implements IPeripheral
                 // setTextColour/setTextColor
                 int colour = TermAPI.parseColour( args );
                 terminal.setTextColour( colour );
-                return null;
+                return MethodResult.empty();
             }
             case 11:
             case 12:
@@ -169,15 +176,15 @@ public class MonitorPeripheral implements IPeripheral
                 // setBackgroundColour/setBackgroundColor
                 int colour = TermAPI.parseColour( args );
                 terminal.setBackgroundColour( colour );
-                return null;
+                return MethodResult.empty();
             }
             case 13:
             case 14:
             {
                 // isColour/isColor
-                return new Object[] {
+                return MethodResult.of(
                     monitor.isColour()
-                };
+                );
             }
             case 15:
             case 16:
@@ -204,7 +211,7 @@ public class MonitorPeripheral implements IPeripheral
 
                 terminal.blit( text, textColour, backgroundColour );
                 terminal.setCursorPos( terminal.getCursorX() + text.length(), terminal.getCursorY() );
-                return null;
+                return MethodResult.empty();
             }
             case 20:
             case 21:
@@ -224,7 +231,7 @@ public class MonitorPeripheral implements IPeripheral
                     double b = getReal( args, 3 );
                     TermAPI.setColour( terminal, colour, r, g, b );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 22:
             case 23:
@@ -236,17 +243,25 @@ public class MonitorPeripheral implements IPeripheral
 
                 if( palette != null )
                 {
-                    return ArrayUtils.toObject( palette.getColour( colour ) );
+                    return MethodResult.of( (Object[]) ArrayUtils.toObject( palette.getColour( colour ) ) );
                 }
-                return null;
+                return MethodResult.empty();
             }
             case 24:
             {
                 // getTextScale
-                return new Object[] { monitor.getTextScale() / 2.0 };
+                return MethodResult.of( monitor.getTextScale() / 2.0 );
             }
         }
-        return null;
+        return MethodResult.empty();
+    }
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull IComputerAccess access, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( access, (ICallContext) context, method, arguments ).evaluate( context );
     }
 
     @Override
@@ -266,7 +281,7 @@ public class MonitorPeripheral implements IPeripheral
     {
         if( other != null && other instanceof MonitorPeripheral )
         {
-            MonitorPeripheral otherMonitor = (MonitorPeripheral)other;
+            MonitorPeripheral otherMonitor = (MonitorPeripheral) other;
             if( otherMonitor.m_monitor == this.m_monitor )
             {
                 return true;

src/main/java/dan200/computercraft/shared/peripheral/printer/PrinterPeripheral.java

@@ -6,13 +6,16 @@
 
 package dan200.computercraft.shared.peripheral.printer;
 
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.core.terminal.Terminal;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.getInt;
 import static dan200.computercraft.core.apis.ArgumentHelper.optString;
@@ -50,8 +53,9 @@ public class PrinterPeripheral implements IPeripheral
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -68,7 +72,7 @@ public class PrinterPeripheral implements IPeripheral
                 Terminal page = getCurrentPage();
                 page.write( text );
                 page.setCursorPos( page.getCursorX() + text.length(), page.getCursorY() );
-                return null;
+                return MethodResult.empty();
             }
             case 1:
             {
@@ -77,7 +81,7 @@ public class PrinterPeripheral implements IPeripheral
                 int y = getInt( args, 1 ) - 1;
                 Terminal page = getCurrentPage();
                 page.setCursorPos( x, y );
-                return null;
+                return MethodResult.empty();
             }
             case 2:
             {
@@ -85,7 +89,7 @@ public class PrinterPeripheral implements IPeripheral
                 Terminal page = getCurrentPage();
                 int x = page.getCursorX();
                 int y = page.getCursorY();
-                return new Object[] { x + 1, y + 1 };
+                return MethodResult.of( x + 1, y + 1 );
             }
             case 3:
             {
@@ -93,23 +97,23 @@ public class PrinterPeripheral implements IPeripheral
                 Terminal page = getCurrentPage();
                 int width = page.getWidth();
                 int height = page.getHeight();
-                return new Object[] { width, height };
+                return MethodResult.of( width, height );
             }
             case 4:
             {
                 // newPage
-                return new Object[] { m_printer.startNewPage() };
+                return MethodResult.of( m_printer.startNewPage() );
             }
             case 5:
             {
                 // endPage
                 getCurrentPage();
-                return new Object[] { m_printer.endCurrentPage() };
+                return MethodResult.of( m_printer.endCurrentPage() );
             }
             case 6:
             {
                 // getInkLevel
-                return new Object[] { m_printer.getInkLevel() };
+                return MethodResult.of( m_printer.getInkLevel() );
             }
             case 7:
             {
@@ -117,20 +121,28 @@ public class PrinterPeripheral implements IPeripheral
                 String title = optString( args, 0, "" );
                 getCurrentPage();
                 m_printer.setPageTitle( title );
-                return null;
+                return MethodResult.empty();
             }
             case 8:
             {
                 // getPaperLevel
-                return new Object[] { m_printer.getPaperLevel() };
+                return MethodResult.of( m_printer.getPaperLevel() );
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
 
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull IComputerAccess access, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( access, (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
     @Override
     public boolean equals( IPeripheral other )
     {

src/main/java/dan200/computercraft/shared/peripheral/speaker/SpeakerPeripheral.java

@@ -7,9 +7,7 @@
 package dan200.computercraft.shared.peripheral.speaker;
 
 import dan200.computercraft.ComputerCraft;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.ILuaTask;
-import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import net.minecraft.util.ResourceLocation;
@@ -98,21 +96,22 @@ public class SpeakerPeripheral implements IPeripheral {
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computerAccess, @Nonnull ILuaContext context, int methodIndex, @Nonnull Object[] args ) throws LuaException
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int methodIndex, @Nonnull Object[] args ) throws LuaException
     {
         switch( methodIndex )
         {
             // playSound
             case 0:
             {
-                return playSound(args, context, false);
+                return MethodResult.of( playSound( args, context, false ) );
             }
 
             // playNote
             case 1:
             {
-                return playNote(args, context);
+                return MethodResult.of( playNote( args, context ) );
             }
 
             default:
@@ -123,8 +122,16 @@ public class SpeakerPeripheral implements IPeripheral {
         }
     }
 
-    @Nonnull
-    private synchronized Object[] playNote( Object[] arguments, ILuaContext context ) throws LuaException
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull IComputerAccess access, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( access, (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
+
+    private synchronized boolean playNote( Object[] arguments, ICallContext context ) throws LuaException
     {
         String name = getString(arguments, 0);
         float volume = (float) optReal( arguments, 1, 1.0 );
@@ -137,7 +144,7 @@ public class SpeakerPeripheral implements IPeripheral {
         }
 
         // If the resource location for note block notes changes, this method call will need to be updated
-        Object[] returnValue = playSound(
+        boolean success = playSound(
             new Object[] {
                 "block.note." + name,
                 (double)Math.min( volume, 3f ),
@@ -145,16 +152,15 @@ public class SpeakerPeripheral implements IPeripheral {
             }, context, true
         );
 
-        if( returnValue[0] instanceof Boolean && (Boolean) returnValue[0] )
+        if( success )
         {
             m_notesThisTick.incrementAndGet();
         }
 
-        return returnValue;
+        return success;
     }
 
-    @Nonnull
-    private synchronized Object[] playSound( Object[] arguments, ILuaContext context, boolean isNote ) throws LuaException
+    private synchronized boolean playSound( Object[] arguments, ICallContext context, boolean isNote ) throws LuaException
     {
         String name = getString(arguments, 0);
         float volume = (float) optReal( arguments, 1, 1.0 );
@@ -184,16 +190,16 @@ public class SpeakerPeripheral implements IPeripheral {
                 });
 
                 m_lastPlayTime = m_clock;
-                return new Object[]{true}; // Success, return true
+                return true; // Success, return true
             }
             else
             {
-                return new Object[]{false}; // Failed - sound not existent, return false
+                return false; // Failed - sound not existent, return false
             }
         }
         else
         {
-            return new Object[]{false}; // Failed - rate limited, return false
+            return false; // Failed - rate limited, return false
         }
     }
 }

src/main/java/dan200/computercraft/shared/pocket/apis/PocketAPI.java

@@ -7,9 +7,7 @@
 package dan200.computercraft.shared.pocket.apis;
 
 import dan200.computercraft.ComputerCraft;
-import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.pocket.IPocketUpgrade;
 import dan200.computercraft.shared.pocket.core.PocketServerComputer;
 import dan200.computercraft.shared.util.InventoryUtil;
@@ -21,6 +19,7 @@ import net.minecraft.util.NonNullList;
 import net.minecraftforge.items.wrapper.PlayerMainInvWrapper;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 public class PocketAPI implements ILuaAPI
 {
@@ -49,14 +48,15 @@ public class PocketAPI implements ILuaAPI
         };
     }
 
+    @Nonnull
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
     {
         switch( method )
         {
             case 0:
                 // equipBack
-                return context.executeMainThreadTask( () ->
+                return MethodResult.onMainThread( () ->
                 {
                     if( !(m_computer.getEntity() instanceof EntityPlayer) )
                     {
@@ -94,12 +94,12 @@ public class PocketAPI implements ILuaAPI
                     // Set the new upgrade
                     m_computer.setUpgrade( newUpgrade );
 
-                    return null;
+                    return MethodResult.empty();
                 } );
 
             case 1:
                 // unequipBack
-                return context.executeMainThreadTask( () ->
+                return MethodResult.onMainThread( () ->
                 {
                     if( !(m_computer.getEntity() instanceof EntityPlayer) )
                     {
@@ -125,13 +125,21 @@ public class PocketAPI implements ILuaAPI
                         }
                     }
 
-                    return null;
+                    return MethodResult.empty();
                 } );
             default:
-                return null;
+                return MethodResult.empty();
         }
     }
 
+    @Override
+    @Nullable
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
     private static IPocketUpgrade findUpgrade( NonNullList<ItemStack> inv, int start, IPocketUpgrade previous )
     {
         for( int i = 0; i < inv.size(); i++ )

src/main/java/dan200/computercraft/shared/turtle/apis/TurtleAPI.java

@@ -6,9 +6,7 @@
 
 package dan200.computercraft.shared.turtle.apis;
 
-import dan200.computercraft.api.lua.ILuaAPI;
-import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.*;
 import dan200.computercraft.api.turtle.ITurtleAccess;
 import dan200.computercraft.api.turtle.ITurtleCommand;
 import dan200.computercraft.api.turtle.TurtleSide;
@@ -22,6 +20,7 @@ import net.minecraft.item.ItemStack;
 import net.minecraftforge.common.MinecraftForge;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
@@ -99,9 +98,9 @@ public class TurtleAPI implements ILuaAPI
         };
     }
     
-    private Object[] tryCommand( ILuaContext context, ITurtleCommand command ) throws LuaException, InterruptedException
+    private MethodResult tryCommand( ITurtleCommand command ) throws LuaException
     {
-        return m_turtle.executeCommand( context, command );
+        return m_turtle.executeCommand( command );
     }
 
     private int parseSlotNumber( Object[] arguments, int index ) throws LuaException
@@ -155,7 +154,8 @@ public class TurtleAPI implements ILuaAPI
     }
 
     @Override
-    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException, InterruptedException
+    @Nonnull
+    public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
         switch( method )
         {
@@ -163,89 +163,89 @@ public class TurtleAPI implements ILuaAPI
             {
                 // forward
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleMoveCommand( MoveDirection.Forward ) );
+                return tryCommand( new TurtleMoveCommand( MoveDirection.Forward ) );
             }
             case 1:
             {
                 // back
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleMoveCommand( MoveDirection.Back ) );
+                return tryCommand( new TurtleMoveCommand( MoveDirection.Back ) );
             }
             case 2:
             {
                 // up
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleMoveCommand( MoveDirection.Up ) );
+                return tryCommand( new TurtleMoveCommand( MoveDirection.Up ) );
             }
             case 3:
             {
                 // down
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleMoveCommand( MoveDirection.Down ) );
+                return tryCommand( new TurtleMoveCommand( MoveDirection.Down ) );
             }
             case 4:
             {
                 // turnLeft
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleTurnCommand( TurnDirection.Left ) );
+                return tryCommand( new TurtleTurnCommand( TurnDirection.Left ) );
             }
             case 5:
             {
                 // turnRight
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleTurnCommand( TurnDirection.Right ) );
+                return tryCommand( new TurtleTurnCommand( TurnDirection.Right ) );
             }
             case 6:
             {
                 // dig
                 Optional<TurtleSide> side = parseSide( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleDigCommand( InteractDirection.Forward, side ) );
+                return tryCommand( new TurtleDigCommand( InteractDirection.Forward, side ) );
             }
             case 7:
             {
                 // digUp
                 Optional<TurtleSide> side = parseSide( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleDigCommand( InteractDirection.Up, side ) );
+                return tryCommand( new TurtleDigCommand( InteractDirection.Up, side ) );
             }
             case 8:
             {
                 // digDown
                 Optional<TurtleSide> side = parseSide( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleDigCommand( InteractDirection.Down, side ) );
+                return tryCommand( new TurtleDigCommand( InteractDirection.Down, side ) );
             }
             case 9:
             {
                 // place
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtlePlaceCommand( InteractDirection.Forward, args ) );
+                return tryCommand( new TurtlePlaceCommand( InteractDirection.Forward, args ) );
             }
             case 10:
             {
                 // placeUp
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtlePlaceCommand( InteractDirection.Up, args ) );
+                return tryCommand( new TurtlePlaceCommand( InteractDirection.Up, args ) );
             }
             case 11:
             {
                 // placeDown
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtlePlaceCommand( InteractDirection.Down, args ) );
+                return tryCommand( new TurtlePlaceCommand( InteractDirection.Down, args ) );
             }
             case 12:
             {
                 // drop
                 int count = parseCount( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleDropCommand( InteractDirection.Forward, count ) );
+                return tryCommand( new TurtleDropCommand( InteractDirection.Forward, count ) );
             }
             case 13:
             {
                 // select
                 int slot = parseSlotNumber( args, 0 );
-                return tryCommand( context, new TurtleSelectCommand( slot ) );
+                return tryCommand( new TurtleSelectCommand( slot ) );
             }
             case 14:
             {
@@ -254,11 +254,11 @@ public class TurtleAPI implements ILuaAPI
                 ItemStack stack = m_turtle.getInventory().getStackInSlot( slot );
                 if( !stack.isEmpty() )
                 {
-                    return new Object[] { stack.getCount() };
+                    return MethodResult.of( stack.getCount() );
                 }
                 else
                 {
-                    return new Object[] { 0 };
+                    return MethodResult.of( 0 );
                 }
             }
             case 15:
@@ -268,172 +268,172 @@ public class TurtleAPI implements ILuaAPI
                 ItemStack stack = m_turtle.getInventory().getStackInSlot( slot );
                 if( !stack.isEmpty() )
                 {
-                    return new Object[] {
+                    return MethodResult.of(
                         Math.min( stack.getMaxStackSize(), 64 ) - stack.getCount()
-                    };
+                    );
                 }
-                return new Object[] { 64 };
+                return MethodResult.of( 64 );
             }
             case 16:
             {
                 // detect
-                return tryCommand( context, new TurtleDetectCommand( InteractDirection.Forward ) );
+                return tryCommand( new TurtleDetectCommand( InteractDirection.Forward ) );
             }
             case 17:
             {
                 // detectUp
-                return tryCommand( context, new TurtleDetectCommand( InteractDirection.Up ) );
+                return tryCommand( new TurtleDetectCommand( InteractDirection.Up ) );
             }
             case 18:
             {
                 // detectDown
-                return tryCommand( context, new TurtleDetectCommand( InteractDirection.Down ) );
+                return tryCommand( new TurtleDetectCommand( InteractDirection.Down ) );
             }
             case 19:
             {
                 // compare
-                return tryCommand( context, new TurtleCompareCommand( InteractDirection.Forward ) );
+                return tryCommand( new TurtleCompareCommand( InteractDirection.Forward ) );
             }
             case 20:
             {
                 // compareUp
-                return tryCommand( context, new TurtleCompareCommand( InteractDirection.Up ) );
+                return tryCommand( new TurtleCompareCommand( InteractDirection.Up ) );
             }
             case 21:
             {
                 // compareDown
-                return tryCommand( context, new TurtleCompareCommand( InteractDirection.Down ) );
+                return tryCommand( new TurtleCompareCommand( InteractDirection.Down ) );
             }
             case 22:
             {
                 // attack
                 Optional<TurtleSide> side = parseSide( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleAttackCommand( InteractDirection.Forward, side ) );
+                return tryCommand( new TurtleAttackCommand( InteractDirection.Forward, side ) );
             }
             case 23:
             {
                 // attackUp
                 Optional<TurtleSide> side = parseSide( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleAttackCommand( InteractDirection.Up, side ) );
+                return tryCommand( new TurtleAttackCommand( InteractDirection.Up, side ) );
             }
             case 24:
             {
                 // attackDown
                 Optional<TurtleSide> side = parseSide( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleAttackCommand( InteractDirection.Down, side ) );
+                return tryCommand( new TurtleAttackCommand( InteractDirection.Down, side ) );
             }
             case 25:
             {
                 // dropUp
                 int count = parseCount( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleDropCommand( InteractDirection.Up, count ) );
+                return tryCommand( new TurtleDropCommand( InteractDirection.Up, count ) );
             }
             case 26:
             {
                 // dropDown
                 int count = parseCount( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleDropCommand( InteractDirection.Down, count ) );
+                return tryCommand( new TurtleDropCommand( InteractDirection.Down, count ) );
             }
             case 27:
             {
                 // suck
                 int count = parseCount( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleSuckCommand( InteractDirection.Forward, count ) );
+                return tryCommand( new TurtleSuckCommand( InteractDirection.Forward, count ) );
             }
             case 28:
             {
                 // suckUp
                 int count = parseCount( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleSuckCommand( InteractDirection.Up, count ) );
+                return tryCommand( new TurtleSuckCommand( InteractDirection.Up, count ) );
             }
             case 29:
             {
                 // suckDown
                 int count = parseCount( args, 0 );
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleSuckCommand( InteractDirection.Down, count ) );
+                return tryCommand( new TurtleSuckCommand( InteractDirection.Down, count ) );
             }
             case 30:
             {
                 // getFuelLevel
                 if( m_turtle.isFuelNeeded() )
                 {
-                    return new Object[] { m_turtle.getFuelLevel() };
+                    return MethodResult.of( m_turtle.getFuelLevel() );
                 }
                 else
                 {
-                    return new Object[] { "unlimited" };
+                    return MethodResult.of( "unlimited" );
                 }
             }
             case 31:
             {
                 // refuel
                 int count = parseCount( args, 0 );
-                return tryCommand( context, new TurtleRefuelCommand( count ) );
+                return tryCommand( new TurtleRefuelCommand( count ) );
             }
             case 32:
             {
                 // compareTo
                 int slot = parseSlotNumber( args, 0 );
-                return tryCommand( context, new TurtleCompareToCommand( slot ) );
+                return tryCommand( new TurtleCompareToCommand( slot ) );
             }
             case 33:
             {
                 // transferTo
                 int slot = parseSlotNumber( args, 0 );
                 int count = parseCount( args, 1 );
-                return tryCommand( context, new TurtleTransferToCommand( slot, count ) );
+                return tryCommand( new TurtleTransferToCommand( slot, count ) );
             }
             case 34:
             {
                 // getSelectedSlot
-                return new Object[] { m_turtle.getSelectedSlot() + 1 };
+                return MethodResult.of( m_turtle.getSelectedSlot() + 1 );
             }
             case 35:
             {
                 // getFuelLimit
                 if( m_turtle.isFuelNeeded() )
                 {
-                    return new Object[] { m_turtle.getFuelLimit() };
+                    return MethodResult.of( m_turtle.getFuelLimit() );
                 }
                 else
                 {
-                    return new Object[] { "unlimited" };
+                    return MethodResult.of( "unlimited" );
                 }
             }
             case 36:
             {
                 // equipLeft
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleEquipCommand( TurtleSide.Left ) );
+                return tryCommand( new TurtleEquipCommand( TurtleSide.Left ) );
             }
             case 37:
             {
                 // equipRight
                 m_environment.addTrackingChange( TrackingField.TURTLE_OPS );
-                return tryCommand( context, new TurtleEquipCommand( TurtleSide.Right ) );
+                return tryCommand( new TurtleEquipCommand( TurtleSide.Right ) );
             }
             case 38:
             {
                 // inspect
-                return tryCommand( context, new TurtleInspectCommand( InteractDirection.Forward ) );
+                return tryCommand( new TurtleInspectCommand( InteractDirection.Forward ) );
             }
             case 39:
             {
                 // inspectUp
-                return tryCommand( context, new TurtleInspectCommand( InteractDirection.Up ) );
+                return tryCommand( new TurtleInspectCommand( InteractDirection.Up ) );
             }
             case 40:
             {
                 // inspectDown
-                return tryCommand( context, new TurtleInspectCommand( InteractDirection.Down ) );
+                return tryCommand( new TurtleInspectCommand( InteractDirection.Down ) );
             }
             case 41:
             {
@@ -455,20 +455,28 @@ public class TurtleAPI implements ILuaAPI
                     TurtleActionEvent event = new TurtleActionEvent( m_turtle, TurtleAction.INSPECT_ITEM );
                     if( MinecraftForge.EVENT_BUS.post( event ) )
                     {
-                        return new Object[] { false, event.getFailureMessage() };
+                        return MethodResult.of( false, event.getFailureMessage() );
                     }
 
-                    return new Object[] { table };
+                    return MethodResult.of( table );
                 }
                 else
                 {
-                    return new Object[] { null };
+                    return MethodResult.of( new Object[] { null } );
                 }
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
+
+    @Override
+    @Nullable
+    @Deprecated
+    public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+    }
 }

src/main/java/dan200/computercraft/shared/turtle/core/TurtleBrain.java

@@ -10,7 +10,9 @@ import com.google.common.base.Objects;
 import com.mojang.authlib.GameProfile;
 import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.ILuaFunction;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.api.turtle.*;
 import dan200.computercraft.shared.computer.blocks.ComputerProxy;
@@ -761,6 +763,7 @@ public class TurtleBrain implements ITurtleAccess
 
     @Nonnull
     @Override
+    @Deprecated
     public Object[] executeCommand( @Nonnull ILuaContext context, @Nonnull ITurtleCommand command ) throws LuaException, InterruptedException
     {
         if( getWorld().isRemote )
@@ -787,6 +790,38 @@ public class TurtleBrain implements ITurtleAccess
         }
     }
 
+    @Nonnull
+    @Override
+    public MethodResult executeCommand( @Nonnull ITurtleCommand command )
+    {
+        if( getWorld().isRemote )
+        {
+            throw new UnsupportedOperationException();
+        }
+
+        // Issue command
+        int commandID = issueCommand( command );
+
+        // Wait for response
+        return MethodResult.pullEvent( "turtle_response", new ILuaFunction()
+        {
+            @Nonnull
+            @Override
+            public MethodResult call( Object[] response )
+            {
+                if( response.length >= 3 && response[ 1 ] instanceof Number && ((Number) response[ 1 ]).intValue() == commandID
+                    && response[ 2 ] instanceof Boolean )
+                {
+                    Object[] returnValues = new Object[ response.length - 2 ];
+                    System.arraycopy( response, 2, returnValues, 0, returnValues.length );
+                    return MethodResult.of( returnValues );
+                }
+
+                return MethodResult.pullEvent( "turtle_response", this );
+            }
+        } );
+    }
+
     @Override
     public void playAnimation( @Nonnull TurtleAnimation animation )
     {

src/main/java/dan200/computercraft/shared/turtle/upgrades/CraftingTablePeripheral.java

@@ -6,19 +6,21 @@
 
 package dan200.computercraft.shared.turtle.upgrades;
 
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.api.turtle.ITurtleAccess;
 import dan200.computercraft.shared.turtle.core.TurtleCraftCommand;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import static dan200.computercraft.core.apis.ArgumentHelper.optInt;
 
-public class CraftingTablePeripheral
-    implements IPeripheral
+public class CraftingTablePeripheral implements IPeripheral
 {
     private final ITurtleAccess m_turtle;
 
@@ -26,7 +28,7 @@ public class CraftingTablePeripheral
     {
         m_turtle = turtle;
     }
-            
+
     // IPeripheral implementation
 
     @Nonnull
@@ -35,7 +37,7 @@ public class CraftingTablePeripheral
     {
         return "workbench";
     }
-       
+
     @Nonnull
     @Override
     public String[] getMethodNames()
@@ -44,7 +46,7 @@ public class CraftingTablePeripheral
             "craft",
         };
     }
-        
+
     private int parseCount( Object[] arguments ) throws LuaException
     {
         int count = optInt( arguments, 0, 64 );
@@ -54,9 +56,10 @@ public class CraftingTablePeripheral
         }
         return count;
     }
-    
+
     @Override
-    public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    @Nonnull
+    public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
     {
         switch( method )
         {
@@ -64,15 +67,24 @@ public class CraftingTablePeripheral
             {
                 // craft
                 final int limit = parseCount( arguments );
-                return m_turtle.executeCommand( context, new TurtleCraftCommand( limit ) );
+                return m_turtle.executeCommand( new TurtleCraftCommand( limit ) );
             }
             default:
             {
-                return null;
+                return MethodResult.empty();
             }
         }
     }
 
+
+    @Nullable
+    @Override
+    @Deprecated
+    public Object[] callMethod( @Nonnull IComputerAccess access, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+    {
+        return callMethod( access, (ICallContext) context, method, arguments ).evaluate( context );
+    }
+
     @Override
     public boolean equals( IPeripheral other )
     {

src/test/java/dan200/computercraft/core/computer/FakeComputerEnvironment.java

@@ -0,0 +1,91 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.computer;
+
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.api.filesystem.IMount;
+import dan200.computercraft.api.filesystem.IWritableMount;
+import dan200.computercraft.core.filesystem.FileMount;
+import net.minecraftforge.fml.common.Loader;
+
+import java.io.File;
+import java.io.InputStream;
+import java.net.URL;
+
+public class FakeComputerEnvironment implements IComputerEnvironment
+{
+    private final boolean colour;
+    private final int id;
+
+    public FakeComputerEnvironment( int id, boolean colour )
+    {
+        this.colour = colour;
+        this.id = id;
+    }
+
+    @Override
+    public int getDay()
+    {
+        return 0;
+    }
+
+    @Override
+    public double getTimeOfDay()
+    {
+        return 0;
+    }
+
+    @Override
+    public boolean isColour()
+    {
+        return colour;
+    }
+
+    @Override
+    public int assignNewID()
+    {
+        return id;
+    }
+
+    @Override
+    public IWritableMount createSaveDirMount( String subPath, long capacity )
+    {
+        return new FileMount( new File( "computer/" + subPath ), capacity );
+    }
+
+    @Override
+    public IMount createResourceMount( String domain, String subPath )
+    {
+        String fullPath = "assets/" + domain + "/" + subPath;
+        URL url = ComputerCraft.class.getProtectionDomain().getCodeSource().getLocation();
+        File file = new File( url.getPath(), fullPath );
+        if( !file.exists() ) file = new File( "src/main/resources", fullPath );
+
+        if( !file.exists() ) throw new RuntimeException( "Cannot find ROM in " + file );
+
+        return new FileMount( file, 0 );
+    }
+
+    @Override
+    public InputStream createResourceFile( String domain, String subPath )
+    {
+        String fullPath = "assets/" + domain + "/" + subPath;
+        return ComputerCraft.class.getClassLoader().getResourceAsStream( fullPath );
+    }
+
+    @Override
+    public long getComputerSpaceLimit()
+    {
+        return ComputerCraft.computerSpaceLimit;
+    }
+
+    @Override
+    public String getHostString()
+    {
+        return "ComputerCraft ${version} (Minecraft " + Loader.MC_VERSION + ")";
+    }
+}

src/test/java/dan200/computercraft/core/computer/RunOnComputer.java

@@ -0,0 +1,155 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.computer;
+
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.api.lua.*;
+import dan200.computercraft.core.terminal.Terminal;
+import org.apache.logging.log4j.LogManager;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.io.OutputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.Objects;
+import java.util.function.Consumer;
+
+import static org.junit.Assert.fail;
+
+public final class RunOnComputer
+{
+    public static final int STARTUP_TIMEOUT = 10;
+    public static final int RUN_TIMEOUT = 100;
+
+    public static void run( String task ) throws Exception
+    {
+        run( task, x -> {
+        } );
+    }
+
+    public static void run( String task, Consumer<Computer> setup ) throws Exception
+    {
+        if( ComputerCraft.log == null ) ComputerCraft.log = LogManager.getLogger( "computercraft" );
+        ComputerCraft.logPeripheralErrors = true;
+
+        // Setup computer
+        Terminal terminal = new Terminal( ComputerCraft.terminalWidth_computer, ComputerCraft.terminalHeight_computer );
+        Computer computer = new Computer( new FakeComputerEnvironment( 0, true ), terminal, 0 );
+
+        // Register APIS
+        TestAPI api = new TestAPI( computer );
+        computer.addAPI( api );
+        setup.accept( computer );
+
+        // Setup the startup file
+        try( OutputStream stream = computer.getRootMount().openForWrite( "startup.lua" ) )
+        {
+            String program = "" +
+                "local function exec()\n" +
+                "  " + task + "\n" +
+                "end\n" +
+                "test.finish(pcall(exec))\n";
+            stream.write( program.getBytes( StandardCharsets.UTF_8 ) );
+        }
+
+        // Turn on
+        ComputerThread.start();
+        computer.turnOn();
+
+        // Run until shutdown or we timeout
+        boolean everOn = false;
+        int ticks = 0;
+        do
+        {
+            computer.advance( 0.05 );
+            MainThread.executePendingTasks();
+
+            Thread.sleep( 50 );
+            ticks++;
+            everOn |= computer.isOn();
+        }
+        while( (computer.isOn() || (!everOn && ticks < STARTUP_TIMEOUT)) && ticks <= RUN_TIMEOUT );
+
+        // If we never finished (say, startup errored) then print the terminal. Otherwise throw the error
+        // where needed.
+        if( !api.finished )
+        {
+            int height = terminal.getHeight() - 1;
+            while( height >= 0 && terminal.getLine( height ).toString().trim().isEmpty() ) height--;
+            for( int y = 0; y <= height; y++ )
+            {
+                System.out.printf( "%2d | %s\n", y + 1, terminal.getLine( y ) );
+            }
+
+            fail( "Computer never finished" );
+        }
+        else if( api.error != null )
+        {
+            fail( api.error );
+        }
+
+        ComputerThread.stop();
+    }
+
+    private static class TestAPI implements ILuaAPI
+    {
+        private final Computer computer;
+
+        private boolean finished = false;
+        private String error;
+
+        private TestAPI( Computer computer )
+        {
+            this.computer = computer;
+        }
+
+        @Override
+        public String[] getNames()
+        {
+            return new String[]{ "test" };
+        }
+
+        @Nonnull
+        @Override
+        public String[] getMethodNames()
+        {
+            return new String[]{ "log", "finish" };
+        }
+
+        @Nullable
+        @Override
+        @Deprecated
+        public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+        {
+            return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+        }
+
+        @Nonnull
+        @Override
+        public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments )
+        {
+            switch( method )
+            {
+                case 0:
+                    ComputerCraft.log.info( Objects.toString( arguments.length <= 0 ? null : arguments[0] ) );
+                    return MethodResult.empty();
+                case 1:
+                {
+                    if( arguments.length <= 0 || arguments[0] == null || arguments[0] == Boolean.FALSE )
+                    {
+                        error = Objects.toString( arguments.length <= 1 ? null : arguments[1] );
+                    }
+                    finished = true;
+                    computer.shutdown();
+                    return MethodResult.empty();
+                }
+                default:
+                    return MethodResult.empty();
+            }
+        }
+    }
+}

src/test/java/dan200/computercraft/core/lua/CobaltWrapperFunctionTest.java

@@ -0,0 +1,243 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2018. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.lua;
+
+import dan200.computercraft.api.lua.*;
+import dan200.computercraft.core.computer.RunOnComputer;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.stream.Collectors;
+
+
+@RunWith( Parameterized.class )
+public class CobaltWrapperFunctionTest
+{
+    @Parameterized.Parameter( 0 )
+    public String name;
+
+    @Parameterized.Parameter( 1 )
+    public String code;
+
+    @Parameterized.Parameters( name = "{0}" )
+    public static Collection<Object[]> parameters()
+    {
+        return Arrays.stream( new Object[][]{
+            new Object[]{ "empty", "assert(select('#', funcs.empty()) == 0)" },
+            new Object[]{ "identity", "assert(select('#', funcs.identity(1, 2, 3)) == 3)" },
+
+            new Object[]{ "pullEvent", "os.queueEvent('test') assert(funcs.pullEvent() == 'test')" },
+            new Object[]{ "pullEventTerminate", "os.queueEvent('terminate') assert(not pcall(funcs.pullEvent))" },
+
+            new Object[]{ "pullEventRaw", "os.queueEvent('test') assert(funcs.pullEventRaw() == 'test')" },
+            new Object[]{ "pullEventRawTerminate", "os.queueEvent('terminate') assert(funcs.pullEventRaw() == 'terminate')" },
+
+            new Object[]{ "mainThread", "assert(funcs.mainThread() == 1)" },
+            new Object[]{ "mainThreadMany", "for i = 1, 4 do assert(funcs.mainThread() == 1) end" }
+        } ).collect( Collectors.toList() );
+    }
+
+    /**
+     * Tests executing functions defined through the {@link MethodResult} API.
+     */
+    @Test
+    public void testMethodResult() throws Exception
+    {
+        RunOnComputer.run( code, c -> c.addAPI( new MethodResultAPI() ) );
+    }
+
+    /**
+     * Tests executing functions defined through the {@link MethodResult} API called with the
+     * {@link ILuaContext} evaluator.
+     */
+    @Test
+    public void testMethodResultEvaluate() throws Exception
+    {
+        RunOnComputer.run( code, c -> c.addAPI( new WrapperAPI( new MethodResultAPI() )
+        {
+            @Nullable
+            @Override
+            @Deprecated
+            public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+            {
+                return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+            }
+        } ) );
+    }
+
+    /**
+     * Tests using {@link MethodResult#then(ILuaFunction)} afterwards
+     */
+    @Test
+    public void testMethodResultThen() throws Exception
+    {
+        RunOnComputer.run( code, c -> c.addAPI( new WrapperAPI( new MethodResultAPI() ) {
+            @Nonnull
+            @Override
+            public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
+            {
+                return super.callMethod( context, method, arguments )
+                    .then( x -> MethodResult.onMainThread( () -> MethodResult.of( x ).then( MethodResult::of ) ) )
+                    .then( MethodResult::of );
+            }
+        } ) );
+    }
+
+    /**
+     * Tests executing functions defined through the {@link ILuaContext} API.
+     */
+    @Test
+    public void testLuaContext() throws Exception
+    {
+        RunOnComputer.run( code, c -> c.addAPI( new LuaContextAPI() ) );
+    }
+
+    /**
+     * Tests executing functions defined through the {@link ILuaContext} API called with the
+     * {@link MethodResult} evaluator.
+     */
+    @Test
+    public void testWithLuaContext() throws Exception
+    {
+        RunOnComputer.run( code, c -> c.addAPI( new WrapperAPI( new LuaContextAPI() )
+        {
+            @Nonnull
+            @Override
+            @SuppressWarnings( "deprecation" )
+            public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
+            {
+                return MethodResult.withLuaContext( c -> callMethod( c, method, arguments ) );
+            }
+        } ) );
+    }
+
+    private static class MethodResultAPI implements ILuaAPI
+    {
+        @Override
+        public String[] getNames()
+        {
+            return new String[]{ "funcs" };
+        }
+
+        @Nonnull
+        @Override
+        public String[] getMethodNames()
+        {
+            return new String[]{ "empty", "identity", "pullEvent", "pullEventRaw", "mainThread" };
+        }
+
+        @Nullable
+        @Override
+        @Deprecated
+        public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+        {
+            return callMethod( (ICallContext) context, method, arguments ).evaluate( context );
+        }
+
+        @Nonnull
+        @Override
+        public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments )
+        {
+            switch( method )
+            {
+                case 0:
+                    return MethodResult.empty();
+                case 1:
+                    return MethodResult.of( arguments );
+                case 2:
+                    return MethodResult.pullEvent( "test" );
+                case 3:
+                    return MethodResult.pullEventRaw( "test" );
+                case 4:
+                    return MethodResult.onMainThread( () -> MethodResult.of( 1 ) );
+                default:
+                    return MethodResult.empty();
+            }
+        }
+    }
+
+    private static class LuaContextAPI implements ILuaAPI
+    {
+        @Override
+        public String[] getNames()
+        {
+            return new String[]{ "funcs" };
+        }
+
+        @Nonnull
+        @Override
+        public String[] getMethodNames()
+        {
+            return new String[]{ "empty", "identity", "pullEvent", "pullEventRaw", "mainThread" };
+        }
+
+        @Nullable
+        @Override
+        @Deprecated
+        public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+        {
+            switch( method )
+            {
+                case 0:
+                    return null;
+                case 1:
+                    return arguments;
+                case 2:
+                    return context.pullEvent( "test" );
+                case 3:
+                    return context.pullEventRaw( "test" );
+                case 4:
+                    return context.executeMainThreadTask( () -> new Object[]{ 1 } );
+                default:
+                    return null;
+            }
+        }
+    }
+
+    public static class WrapperAPI implements ILuaAPI
+    {
+        private final ILuaAPI api;
+
+        public WrapperAPI( ILuaAPI api )
+        {
+            this.api = api;
+        }
+
+        @Override
+        public String[] getNames()
+        {
+            return api.getNames();
+        }
+
+        @Nonnull
+        @Override
+        public String[] getMethodNames()
+        {
+            return api.getMethodNames();
+        }
+
+        @Nullable
+        @Override
+        @Deprecated
+        public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+        {
+            return api.callMethod( context, method, arguments );
+        }
+
+        @Nonnull
+        @Override
+        public MethodResult callMethod( @Nonnull ICallContext context, int method, @Nonnull Object[] arguments ) throws LuaException
+        {
+            return api.callMethod( context, method, arguments );
+        }
+    }
+}

src/test/java/dan200/computercraft/shared/wired/NetworkTest.java

@@ -4,8 +4,9 @@ import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
 import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.api.ComputerCraftAPI;
+import dan200.computercraft.api.lua.ICallContext;
 import dan200.computercraft.api.lua.ILuaContext;
-import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
 import dan200.computercraft.api.network.wired.IWiredElement;
 import dan200.computercraft.api.network.wired.IWiredNetwork;
 import dan200.computercraft.api.network.wired.IWiredNetworkChange;
@@ -249,7 +250,7 @@ public class NetworkTest
     }
 
     @Test
-    @Ignore("Takes a long time to run, mostly for stress testing")
+    @Ignore( "Takes a long time to run, mostly for stress testing" )
     public void testLarge()
     {
         final int BRUTE_SIZE = 16;
@@ -410,11 +411,19 @@ public class NetworkTest
 
         @Nullable
         @Override
-        public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
+        @Deprecated
+        public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments )
         {
             return new Object[0];
         }
 
+        @Nonnull
+        @Override
+        public MethodResult callMethod( @Nonnull IComputerAccess computer, @Nonnull ICallContext context, int method, @Nonnull Object[] arguments )
+        {
+            return MethodResult.empty();
+        }
+
         @Override
         public boolean equals( @Nullable IPeripheral other )
         {
@@ -427,7 +436,7 @@ public class NetworkTest
         private final int size;
         private final T[] box;
 
-        @SuppressWarnings("unchecked")
+        @SuppressWarnings( "unchecked" )
         public Grid( int size )
         {
             this.size = size;