Rewrite argument validation

This uses a new utility class ArgumentHelper, which provides convenience
methods for parsing arguments from an array of Objects.

The format of error messages has also changed. It now follows a format
similar to Lua's native error messages - including the invalid argument
index, the expected type and the type actually received.

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

@@ -0,0 +1,246 @@
+package dan200.computercraft.core.apis;
+
+import dan200.computercraft.api.lua.LuaException;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.util.Map;
+
+/**
+ * Various helpers for arguments
+ */
+public final class ArgumentHelper
+{
+    private ArgumentHelper()
+    {
+        throw new IllegalStateException( "Cannot instantiate singleton " + getClass().getName() );
+    }
+
+    @Nonnull
+    public static String getType( @Nullable Object type )
+    {
+        if( type == null ) return "nil";
+        if( type instanceof String ) return "string";
+        if( type instanceof Boolean ) return "boolean";
+        if( type instanceof Number ) return "number";
+        if( type instanceof Map ) return "table";
+
+        Class<?> klass = type.getClass();
+        if( klass.isArray() )
+        {
+            StringBuilder name = new StringBuilder();
+            while( klass.isArray() )
+            {
+                name.append( "[]" );
+                klass = klass.getComponentType();
+            }
+            name.insert( 0, klass.getName() );
+            return name.toString();
+        }
+        else
+        {
+            return klass.getName();
+        }
+    }
+
+    @Nonnull
+    public static LuaException badArgument( int index, @Nonnull String expected, @Nullable Object actual )
+    {
+        return badArgument( index, expected, getType( actual ) );
+    }
+
+    @Nonnull
+    public static LuaException badArgument( int index, @Nonnull String expected, @Nonnull String actual )
+    {
+        return new LuaException( "bad argument #" + (index + 1) + " (" + expected + " expected, got " + actual + ")" );
+    }
+
+    public static double getNumber( @Nonnull Object[] args, int index ) throws LuaException
+    {
+        if( index >= args.length ) throw badArgument( index, "number", "no value" );
+        Object value = args[ index ];
+        if( value instanceof Number )
+        {
+            return ((Number) value).doubleValue();
+        }
+        else
+        {
+            throw badArgument( index, "number", value );
+        }
+    }
+
+    public static int getInt( @Nonnull Object[] args, int index ) throws LuaException
+    {
+        if( index >= args.length ) throw badArgument( index, "number", "no value" );
+        Object value = args[ index ];
+        if( value instanceof Number )
+        {
+            return (int) ((Number) value).longValue();
+        }
+        else
+        {
+            throw badArgument( index, "number", value );
+        }
+    }
+
+    public static double getReal( @Nonnull Object[] args, int index ) throws LuaException
+    {
+        return checkReal( index, getNumber( args, index ) );
+    }
+
+    public static boolean getBoolean( @Nonnull Object[] args, int index ) throws LuaException
+    {
+        if( index >= args.length ) throw badArgument( index, "boolean", "no value" );
+        Object value = args[ index ];
+        if( value instanceof Boolean )
+        {
+            return (Boolean) value;
+        }
+        else
+        {
+            throw badArgument( index, "boolean", value );
+        }
+    }
+
+    @Nonnull
+    public static String getString( @Nonnull Object[] args, int index ) throws LuaException
+    {
+        if( index >= args.length ) throw badArgument( index, "string", "no value" );
+        Object value = args[ index ];
+        if( value instanceof String )
+        {
+            return (String) value;
+        }
+        else
+        {
+            throw badArgument( index, "string", value );
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    @Nonnull
+    public static Map<Object, Object> getTable( @Nonnull Object[] args, int index ) throws LuaException
+    {
+        if( index >= args.length ) throw badArgument( index, "table", "no value" );
+        Object value = args[ index ];
+        if( value instanceof Map )
+        {
+            return (Map<Object, Object>) value;
+        }
+        else
+        {
+            throw badArgument( index, "table", value );
+        }
+    }
+
+    public static double optNumber( @Nonnull Object[] args, int index, double def ) throws LuaException
+    {
+        Object value = index < args.length ? args[ index ] : null;
+        if( value == null )
+        {
+            return def;
+        }
+        else if( value instanceof Number )
+        {
+            return ((Number) value).doubleValue();
+        }
+        else
+        {
+            throw badArgument( index, "number", value );
+        }
+    }
+
+    public static int optInt( @Nonnull Object[] args, int index, int def ) throws LuaException
+    {
+        Object value = index < args.length ? args[ index ] : null;
+        if( value == null )
+        {
+            return def;
+        }
+        else if( value instanceof Number )
+        {
+            return (int) ((Number) value).longValue();
+        }
+        else
+        {
+            throw badArgument( index, "number", value );
+        }
+    }
+
+    public static double optReal( @Nonnull Object[] args, int index, double def ) throws LuaException
+    {
+        return checkReal( index, optNumber( args, index, def ) );
+    }
+
+    public static boolean optBoolean( @Nonnull Object[] args, int index, boolean def ) throws LuaException
+    {
+        Object value = index < args.length ? args[ index ] : null;
+        if( value == null )
+        {
+            return def;
+        }
+        else if( value instanceof Boolean )
+        {
+            return (Boolean) value;
+        }
+        else
+        {
+            throw badArgument( index, "boolean", value );
+        }
+    }
+
+    public static String optString( @Nonnull Object[] args, int index, String def ) throws LuaException
+    {
+        Object value = index < args.length ? args[ index ] : null;
+        if( value == null )
+        {
+            return def;
+        }
+        else if( value instanceof String )
+        {
+            return (String) value;
+        }
+        else
+        {
+            throw badArgument( index, "string", value );
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    public static Map<Object, Object> optTable( @Nonnull Object[] args, int index, Map<Object, Object> def ) throws LuaException
+    {
+        Object value = index < args.length ? args[ index ] : null;
+        if( value == null )
+        {
+            return def;
+        }
+        else if( value instanceof Map )
+        {
+            return (Map<Object, Object>) value;
+        }
+        else
+        {
+            throw badArgument( index, "table", value );
+        }
+    }
+
+    private static double checkReal( int index, double value ) throws LuaException
+    {
+        if( Double.isNaN( value ) )
+        {
+            throw badArgument( index, "number", "nan" );
+        }
+        else if( value == Double.POSITIVE_INFINITY )
+        {
+            throw badArgument( index, "number", "inf" );
+        }
+        else if( value == Double.NEGATIVE_INFINITY )
+        {
+            throw badArgument( index, "number", "-inf" );
+        }
+        else
+        {
+            return value;
+        }
+    }
+}

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

@@ -11,6 +11,8 @@ import dan200.computercraft.api.lua.LuaException;
 
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getInt;
+
 // Contributed by Nia
 // Based on LuaBit (http://luaforge.net/projects/bit)
  
@@ -24,25 +26,6 @@ public class BitAPI implements ILuaAPI
     private static final int BLSHIFT                  = 5;
     private static final int BLOGIC_RSHIFT              = 6;
     
-    private static int checkInt( Object o, int count ) throws LuaException
-    {
-        if( o instanceof Number )
-        {
-            return (int)(((Number)o).longValue());
-        }
-        else
-        {
-            if( count == 2 )
-            {
-                throw new LuaException( "Expected number, number" );
-            }
-            else
-            {
-                throw new LuaException( "Expected number" );
-            }
-        }
-    }
-    
     public BitAPI( IAPIEnvironment _environment )
     {
     }
@@ -82,31 +65,28 @@ public class BitAPI implements ILuaAPI
     @Override
     public Object[] callMethod( @Nonnull ILuaContext context, int method, @Nonnull Object[] args ) throws LuaException
     {
-        Object a = args.length>0?args[0]:null;
-        Object b = args.length>1?args[1]:null;
- 
         int ret = 0;
         switch(method) {
             case BNOT:
-                ret = ~checkInt(a, 1);
+                ret = ~getInt( args, 0 );
                 break;
             case BAND:
-                ret = checkInt(a, 2) & checkInt(b, 2);
+                ret = getInt( args, 0 ) & getInt( args, 1 );
                 break;
             case BOR:
-                ret = checkInt(a, 2) | checkInt(b, 2);
+                ret = getInt( args, 0 ) | getInt( args, 1 );
                 break;
             case BXOR:
-                ret = checkInt(a, 2) ^ checkInt(b, 2);
+                ret = getInt( args, 0 ) ^ getInt( args, 1 );
                 break;
             case BRSHIFT:
-                ret = checkInt(a, 2) >> checkInt(b, 2);
+                ret = getInt( args, 0 ) >> getInt( args, 1 );
                 break;
             case BLSHIFT:
-                ret = checkInt(a, 2) << checkInt(b, 2);
+                ret = getInt( args, 0 ) << getInt( args, 1 );
                 break;
             case BLOGIC_RSHIFT:
-                ret = checkInt(a, 2) >>> checkInt(b, 2);
+                ret = getInt( args, 0 ) >>> getInt( args, 1 );
                 break;
         }
         

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

@@ -13,6 +13,9 @@ import dan200.computercraft.core.terminal.TextBuffer;
 
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getString;
+import static dan200.computercraft.core.apis.ArgumentHelper.optInt;
+
 public class BufferAPI implements ILuaAPI
 {
     private static class BufferLuaObject implements ILuaObject
@@ -55,81 +58,25 @@ public class BufferAPI implements ILuaAPI
                 case 2:
                 {
                     // read
-                    int start = 0;
+                    int start = optInt( arguments, 0, 0 );
-                    if( arguments.length >= 1 && (arguments[0] != null) )
+                    int end = optInt( arguments, 1, m_buffer.length() );
-                    {
-                        if( !(arguments[0] instanceof Number) )
-                        {
-                            throw new LuaException( "Expected number" );
-                        }
-                        start = ((Number)arguments[1]).intValue() - 1;
-                    }
-                    int end = m_buffer.length();
-                    if( arguments.length >= 2 && (arguments[1] != null) )
-                    {
-                        if( !(arguments[1] instanceof Number) )
-                        {
-                            throw new LuaException( "Expected number, number" );
-                        }
-                        end = ((Number)arguments[1]).intValue();
-                    }
                     return new Object[] { m_buffer.read( start, end ) };
                 }
                 case 3:
                 {
                     // write
-                    if( arguments.length < 1 || !(arguments[0] instanceof String) )
+                    String text = getString( arguments, 0 );
-                    {
+                    int start = optInt( arguments, 1, 0 );
-                        throw new LuaException( "Expected string" );
+                    int end = optInt( arguments, 2, start + text.length() );
-                    }
-                    String text = (String)(arguments[0]);
-                    int start = 0;
-                    if( arguments.length >= 2 && (arguments[1] != null) )
-                    {
-                        if( !(arguments[1] instanceof Number) )
-                        {
-                            throw new LuaException( "Expected string, number" );
-                        }
-                        start = ((Number)arguments[1]).intValue() - 1;
-                    }
-                    int end = start + text.length();
-                    if( arguments.length >= 3 && (arguments[2] != null) )
-                    {
-                        if( !(arguments[2] instanceof Number) )
-                        {
-                            throw new LuaException( "Expected string, number, number" );
-                        }
-                        end = ((Number)arguments[2]).intValue();
-                    }
                     m_buffer.write( text, start, end );
                     return null;
                 }
                 case 4:
                 {
                     // fill
-                    if( arguments.length < 1 || !(arguments[0] instanceof String) )
+                    String text = getString( arguments, 0 );
-                    {
+                    int start = optInt( arguments, 1, 0 );
-                        throw new LuaException( "Expected string" );
+                    int end = optInt( arguments, 2, m_buffer.length() );
-                    }
-                    String text = (String)(arguments[0]);
-                    int start = 0;
-                    if( arguments.length >= 2 && (arguments[1] != null) )
-                    {
-                        if( !(arguments[1] instanceof Number) )
-                        {
-                            throw new LuaException( "Expected string, number" );
-                        }
-                        start = ((Number)arguments[1]).intValue() - 1;
-                    }
-                    int end = m_buffer.length();
-                    if( arguments.length >= 3 && (arguments[2] != null) )
-                    {
-                        if( !(arguments[2] instanceof Number) )
-                        {
-                            throw new LuaException( "Expected string, number, number" );
-                        }
-                        end = ((Number)arguments[2]).intValue();
-                    }
                     m_buffer.fill( text, start, end );
                     return null;
                 }
@@ -184,23 +131,11 @@ public class BufferAPI implements ILuaAPI
         {
             case 0:
             {
-                if( arguments.length < 1 || !(arguments[0] instanceof String) )
+                String text = getString( arguments, 0 );
+                int repetitions = optInt( arguments, 1, 1 );
+                if( repetitions < 0 )
                 {
-                    throw new LuaException( "Expected string" );
+                    throw ArgumentHelper.badArgument( 1, "positive number", Integer.toString( repetitions ) );
-                }
-                String text = (String)(arguments[0]);
-                int repetitions = 1;
-                if( arguments.length >= 2 && arguments[1] != null )
-                {
-                    if( !(arguments[1] instanceof Number) )
-                    {
-                        throw new LuaException( "Expected string, number" );
-                    }
-                    repetitions = ((Number)arguments[1]).intValue();
-                    if( repetitions < 0 )
-                    {
-                        throw new LuaException( "Expected positive number" );
-                    }
                 }
                 TextBuffer buffer = new TextBuffer( text, repetitions );
                 return new Object[] { new BufferLuaObject( buffer ) };

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

@@ -21,6 +21,8 @@ import java.io.OutputStream;
 import java.util.HashMap;
 import java.util.Map;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getString;
+
 public class FSAPI implements ILuaAPI
 {
     private IAPIEnvironment m_env;
@@ -89,11 +91,7 @@ public class FSAPI implements ILuaAPI
             case 0:
             {
                 // list
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     String[] results = m_fileSystem.list( path );
                     Map<Object,Object> table = new HashMap<Object,Object>();
@@ -110,32 +108,20 @@ public class FSAPI implements ILuaAPI
             case 1:
             {
                 // combine
-                if( args.length != 2 || args[0] == null || !(args[0] instanceof String) || args[1] == null || !(args[1] instanceof String) )
+                String pathA = getString( args, 0 );
-                {
+                String pathB = getString( args, 1 );
-                    throw new LuaException( "Expected string, string" );
-                }
-                String pathA = (String)args[0];
-                String pathB = (String)args[1];
                 return new Object[] { m_fileSystem.combine( pathA, pathB ) };
             }
             case 2:
             {
                 // getName
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 return new Object[]{ FileSystem.getName( path ) };
             }
             case 3:
             {
                 // getSize
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try
                 {
                     return new Object[]{ m_fileSystem.getSize( path ) };
@@ -148,11 +134,7 @@ public class FSAPI implements ILuaAPI
             case 4:
             {
                 // exists
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     return new Object[]{ m_fileSystem.exists( path ) };
                 } catch( FileSystemException e ) {
@@ -162,11 +144,7 @@ public class FSAPI implements ILuaAPI
             case 5:
             {
                 // isDir
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     return new Object[]{ m_fileSystem.isDir( path ) };
                 } catch( FileSystemException e ) {
@@ -176,11 +154,7 @@ public class FSAPI implements ILuaAPI
             case 6:
             {
                 // isReadOnly
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     return new Object[]{ m_fileSystem.isReadOnly( path ) };
                 } catch( FileSystemException e ) {
@@ -190,11 +164,7 @@ public class FSAPI implements ILuaAPI
             case 7:
             {
                 // makeDir
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     m_fileSystem.makeDir( path );
                     return null;
@@ -205,12 +175,8 @@ public class FSAPI implements ILuaAPI
             case 8:
             {
                 // move
-                if( args.length != 2 || args[0] == null || !(args[0] instanceof String) || args[1] == null || !(args[1] instanceof String) )
+                String path = getString( args, 0 );
-                {
+                String dest = getString( args, 1 );
-                    throw new LuaException( "Expected string, string" );
-                }
-                String path = (String)args[0];
-                String dest = (String)args[1];
                 try {
                     m_fileSystem.move( path, dest );
                     return null;
@@ -221,12 +187,8 @@ public class FSAPI implements ILuaAPI
             case 9:
             {
                 // copy
-                if( args.length != 2 || args[0] == null || !(args[0] instanceof String) || args[1] == null || !(args[1] instanceof String) )
+                String path = getString( args, 0 );
-                {
+                String dest = getString( args, 1 );
-                    throw new LuaException( "Expected string, string" );
-                }
-                String path = (String)args[0];
-                String dest = (String)args[1];
                 try {
                     m_fileSystem.copy( path, dest );
                     return null;
@@ -237,11 +199,7 @@ public class FSAPI implements ILuaAPI
             case 10:
             {
                 // delete
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     m_fileSystem.delete( path );
                     return null;
@@ -252,12 +210,8 @@ public class FSAPI implements ILuaAPI
             case 11:
             {
                 // open
-                if( args.length < 2 || args[0] == null || !(args[0] instanceof String) || args[1] == null || !(args[1] instanceof String) )
+                String path = getString( args, 0 );
-                {
+                String mode = getString( args, 1 );
-                    throw new LuaException( "Expected string, string" );
-                }
-                String path = (String)args[0];
-                String mode = (String)args[1];
                 try {
                     if( mode.equals( "r" ) ) {
                         // Open the file for reading, then create a wrapper around the reader
@@ -300,11 +254,7 @@ public class FSAPI implements ILuaAPI
             case 12:
             {
                 // getDrive
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     if( !m_fileSystem.exists( path ) )
                     {
@@ -318,11 +268,7 @@ public class FSAPI implements ILuaAPI
             case 13:
             {
                 // getFreeSpace
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     long freeSpace = m_fileSystem.getFreeSpace( path );
                     if( freeSpace >= 0 )
@@ -337,11 +283,7 @@ public class FSAPI implements ILuaAPI
             case 14:
             {
                 // find
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 try {
                     String[] results = m_fileSystem.find( path );
                     Map<Object,Object> table = new HashMap<Object,Object>();
@@ -356,11 +298,7 @@ public class FSAPI implements ILuaAPI
             case 15:
             {
                 // getDir
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof String) )
+                String path = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String path = (String)args[0];
                 return new Object[]{ FileSystem.getDirectory( path ) };
             }
             default:

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

@@ -16,6 +16,8 @@ import javax.annotation.Nonnull;
 import java.io.InputStream;
 import java.util.*;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.*;
+
 public class HTTPAPI implements ILuaAPI
 {
     private final IAPIEnvironment m_apiEnvironment;
@@ -155,24 +157,16 @@ public class HTTPAPI implements ILuaAPI
             {
                 // request
                 // Get URL
-                if( args.length < 1 || !(args[0] instanceof String) )
+                String urlString = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String urlString = args[0].toString();
 
                 // Get POST
-                String postString = null;
+                String postString = optString( args, 1, null );
-                if( args.length >= 2 && args[1] instanceof String )
-                {
-                    postString = args[1].toString();
-                }
 
                 // Get Headers
                 Map<String, String> headers = null;
-                if( args.length >= 3 && args[2] instanceof Map )
+                Map<Object, Object> table = optTable( args, 2, null );
+                if( table != null )
                 {
-                    Map<?, ?> table = (Map<?, ?>)args[2];
                     headers = new HashMap<String, String>( table.size() );
                     for( Object key : table.keySet() )
                     {
@@ -210,11 +204,7 @@ public class HTTPAPI implements ILuaAPI
             {
                 // checkURL
                 // Get URL
-                if( args.length < 1 || !(args[0] instanceof String) )
+                String urlString = getString( args, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                String urlString = args[0].toString();
 
                 // Check URL
                 try

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

@@ -13,6 +13,8 @@ import dan200.computercraft.shared.util.StringUtil;
 import javax.annotation.Nonnull;
 import java.util.*;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.*;
+
 public class OSAPI implements ILuaAPI
 {
     private IAPIEnvironment m_apiEnvironment;
@@ -225,21 +227,13 @@ public class OSAPI implements ILuaAPI
             case 0:
             {
                 // queueEvent
-                if( args.length == 0 || args[0] == null || !(args[0] instanceof String) )
+                queueLuaEvent( getString( args, 0 ), trimArray( args, 1 ) );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                queueLuaEvent( (String)args[0], trimArray( args, 1 ) );
                 return null;
             }
             case 1:
             {
                 // startTimer
-                if( args.length < 1 || args[0] == null || !(args[0] instanceof Number) )
+                double timer = getReal( args, 0 );
-                {
-                    throw new LuaException( "Expected number" );
-                }
-                double timer = ((Number)args[0]).doubleValue();
                 synchronized( m_timers )
                 {
                     m_timers.put( m_nextTimerToken, new Timer( (int)Math.round( timer / 0.05 ) ) );
@@ -249,11 +243,7 @@ public class OSAPI implements ILuaAPI
             case 2:
             {
                 // setAlarm
-                if( args.length < 1 || args[0] == null || !(args[0] instanceof Number) )
+                double time = getReal( args, 0 );
-                {
-                    throw new LuaException( "Expected number" );
-                }
-                double time = ((Number)args[0]).doubleValue();
                 if( time < 0.0 || time >= 24.0 )
                 {
                     throw new LuaException( "Number out of range" );
@@ -286,16 +276,8 @@ public class OSAPI implements ILuaAPI
             case 7:
             {
                 // setComputerLabel
-                String label = null;
+                String label = optString( args, 0, null );
-                if( args.length > 0 && args[0] != null )
+                m_apiEnvironment.setLabel( StringUtil.normaliseLabel( label ) );
-                {
-                    if(!(args[0] instanceof String))
-                    {
-                        throw new LuaException( "Expected string or nil" );
-                    }
-                    label = StringUtil.normaliseLabel( (String) args[0] );
-                }
-                m_apiEnvironment.setLabel( label );
                 return null;
             }
             case 8:
@@ -320,13 +302,7 @@ public class OSAPI implements ILuaAPI
             case 11:
             {
                 // time
-                String param = "ingame";
+                String param = optString( args, 0, "ingame" );
-                if (args.length > 0 && args[0] != null) {
-                    if (!(args[0] instanceof String)) {
-                        throw new LuaException("Expected string");
-                    }
-                    param = (String)args[0];
-                }
 
                 if (param.equals("utc")) {
                     // Get Hour of day (UTC)
@@ -351,13 +327,7 @@ public class OSAPI implements ILuaAPI
             case 12:
             {
                 // day
-                String param = "ingame";
+                String param = optString( args, 0, "ingame" );
-                if (args.length > 0 && args[0] != null) {
-                    if (!(args[0] instanceof String)) {
-                        throw new LuaException("Expected string");
-                    }
-                    param = (String)args[0];
-                }
                 if (param.equals("utc")) {
                     // Get numbers of days since 1970-01-01 (utc)
                     Calendar c = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
@@ -381,11 +351,7 @@ public class OSAPI implements ILuaAPI
             case 13:
             {
                 // cancelTimer
-                if( args.length < 1 || args[0] == null || !(args[0] instanceof Number) )
+                int token = getInt( args, 0 );
-                {
-                    throw new LuaException( "Expected number" );
-                }
-                int token = ((Number)args[0]).intValue();
                 synchronized( m_timers )
                 {
                     if( m_timers.containsKey( token ) )
@@ -398,11 +364,7 @@ public class OSAPI implements ILuaAPI
             case 14:
             {
                 // cancelAlarm
-                if( args.length < 1 || args[0] == null || !(args[0] instanceof Number) )
+                int token = getInt( args, 0 );
-                {
-                    throw new LuaException( "Expected number" );
-                }
-                int token = ((Number)args[0]).intValue();
                 synchronized( m_alarms )
                 {
                     if( m_alarms.containsKey( token ) )
@@ -415,13 +377,7 @@ public class OSAPI implements ILuaAPI
             case 15:
             {
                 // epoch
-                String param = "ingame";
+                String param = optString( args, 0, "ingame" );
-                if (args.length > 0 && args[0] != null) {
-                    if (!(args[0] instanceof String)) {
-                        throw new LuaException("Expected string");
-                    }
-                    param = (String)args[0];
-                }
                 if (param.equals("utc")) {
                     // Get utc epoch
                     Calendar c = Calendar.getInstance(TimeZone.getTimeZone("UTC"));

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

@@ -21,6 +21,8 @@ import dan200.computercraft.core.filesystem.FileSystemException;
 import javax.annotation.Nonnull;
 import java.util.*;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getString;
+
 public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChangeListener
 {
     private class PeripheralWrapper implements IComputerAccess
@@ -460,14 +462,10 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
             case 3:
             {
                 // call
-                if( args.length < 2 || args[1] == null || !(args[1] instanceof String) )
+                int side = parseSide( args );
-                {
+                String methodName = getString( args, 1 );
-                    throw new LuaException( "Expected string, string" );
-                }
-                String methodName = (String)args[1];
                 Object[] methodArgs = trimArray( args, 2 );
                 
-                int side = parseSide( args );
                 if( side >= 0 )
                 {
                     PeripheralWrapper p;
@@ -498,11 +496,7 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
 
     private int parseSide( Object[] args ) throws LuaException
     {
-        if( args.length < 1 || args[0] == null || !(args[0] instanceof String) )
+        String side = getString( args, 0 );
-        {
-            throw new LuaException( "Expected string" );
-        }
-        String side = (String)args[0];
         for( int n=0; n<Computer.s_sideNames.length; ++n )
         {
             if( side.equals( Computer.s_sideNames[n] ) )

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

@@ -14,6 +14,8 @@ import javax.annotation.Nonnull;
 import java.util.HashMap;
 import java.util.Map;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.*;
+
 public class RedstoneAPI implements ILuaAPI
 {
     private IAPIEnvironment m_environment;
@@ -86,12 +88,8 @@ public class RedstoneAPI implements ILuaAPI
             case 1:
             {
                 // setOutput
-                if( args.length < 2 || args[0] == null || !(args[0] instanceof String) || args[1] == null || !(args[1] instanceof Boolean) )
-                {
-                    throw new LuaException( "Expected string, boolean" );
-                }
                 int side = parseSide( args );
-                boolean output = (Boolean) args[ 1 ];
+                boolean output = getBoolean( args, 1 );
                 m_environment.setOutput( side, output ? 15 : 0 );
                 return null;
             }
@@ -110,12 +108,8 @@ public class RedstoneAPI implements ILuaAPI
             case 4:
             {
                 // setBundledOutput
-                if( args.length < 2 || args[0] == null || !(args[0] instanceof String) || args[1] == null || !(args[1] instanceof Double) )
-                {
-                    throw new LuaException( "Expected string, number" );
-                }
                 int side = parseSide( args );
-                int output = ((Double)args[1]).intValue();
+                int output = getInt( args, 1 );
                 m_environment.setBundledOutput( side, output );
                 return null;
             }
@@ -134,12 +128,8 @@ public class RedstoneAPI implements ILuaAPI
             case 7:
             {
                 // testBundledInput
-                if( args.length < 2 || args[0] == null || !(args[0] instanceof String) || args[1] == null || !(args[1] instanceof Double) )
-                {
-                    throw new LuaException( "Expected string, number" );
-                }
                 int side = parseSide( args );
-                int mask = ((Double)args[1]).intValue();
+                int mask = getInt( args, 1 );
                 int input = m_environment.getBundledInput( side );
                 return new Object[] { ((input & mask) == mask) };
             }
@@ -147,12 +137,8 @@ public class RedstoneAPI implements ILuaAPI
             case 9:
             {
                 // setAnalogOutput/setAnalogueOutput
-                if( args.length < 2 || args[0] == null || !(args[0] instanceof String) || args[1] == null || !(args[1] instanceof Double) )
-                {
-                    throw new LuaException( "Expected string, number" );
-                }
                 int side = parseSide( args );
-                int output = ((Double)args[1]).intValue();
+                int output = getInt( args, 1 );
                 if( output < 0 || output > 15 )
                 {
                     throw new LuaException( "Expected number in range 0-15" );
@@ -183,11 +169,7 @@ public class RedstoneAPI implements ILuaAPI
     
     private int parseSide( Object[] args ) throws LuaException
     {
-        if( args.length < 1 || args[0] == null || !(args[0] instanceof String) )
+        String side = getString( args, 0 );
-        {
-            throw new LuaException( "Expected string" );
-        }
-        String side = (String)args[0];
         for( int n=0; n<Computer.s_sideNames.length; ++n )
         {
             if( side.equals( Computer.s_sideNames[n] ) )

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

@@ -13,12 +13,10 @@ import dan200.computercraft.core.terminal.Terminal;
 import dan200.computercraft.shared.util.Palette;
 import org.apache.commons.lang3.ArrayUtils;
 
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Set;
-
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.*;
+
 public class TermAPI implements ILuaAPI
 {
     private final Terminal m_terminal;
@@ -86,11 +84,7 @@ public class TermAPI implements ILuaAPI
     
     public static int parseColour( Object[] args ) throws LuaException
     {
-        if( args.length < 1 || args[0] == null || !(args[0] instanceof Double) )
+        int colour = getInt( args, 0 );
-        {
-            throw new LuaException( "Expected number" );
-        }            
-        int colour = (int)((Double)args[0]).doubleValue();
         if( colour <= 0 )
         {
             throw new LuaException( "Colour out of range" );
@@ -144,12 +138,7 @@ public class TermAPI implements ILuaAPI
             case 1:
             {
                 // scroll
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof Double) )
+                int y = getInt( args, 0 );
-                {
-                    throw new LuaException( "Expected number" );
-                }
-                
-                int y = (int)((Double)args[0]).doubleValue();
                 synchronized( m_terminal )
                 {
                     m_terminal.scroll(y);
@@ -159,12 +148,8 @@ public class TermAPI implements ILuaAPI
             case 2:
             {
                 // setCursorPos
-                if( args.length != 2 || args[0] == null || !(args[0] instanceof Double) || args[1] == null || !(args[1] instanceof Double) )
+                int x = getInt( args, 0 ) - 1;
-                {
+                int y = getInt( args, 1 ) - 1;
-                    throw new LuaException( "Expected number, number" );
-                }
-                int x = (int)((Double)args[0]).doubleValue() - 1;
-                int y = (int)((Double)args[1]).doubleValue() - 1;
                 synchronized( m_terminal )
                 {
                     m_terminal.setCursorPos( x, y );
@@ -174,11 +159,7 @@ public class TermAPI implements ILuaAPI
             case 3:
             {
                 // setCursorBlink
-                if( args.length != 1 || args[0] == null || !(args[0] instanceof Boolean) )
+                boolean b = getBoolean( args, 0 );
-                {
-                    throw new LuaException( "Expected boolean" );
-                }
-                boolean b = (Boolean) args[ 0 ];
                 synchronized( m_terminal )
                 {
                     m_terminal.setCursorBlink( b );
@@ -268,14 +249,9 @@ public class TermAPI implements ILuaAPI
             case 18:
             {
                 // blit
-                if( args.length < 3 || !(args[0] instanceof String) || !(args[1] instanceof String) || !(args[2] instanceof String) )
+                String text = getString( args, 0 );
-                {
+                String textColour = getString( args, 1 );
-                    throw new LuaException( "Expected string, string, string" );
+                String backgroundColour = getString( args, 2 );
-                }
-
-                String text = (String)args[0];
-                String textColour = (String)args[1];
-                String backgroundColour = (String)args[2];
                 if( textColour.length() != text.length() || backgroundColour.length() != text.length() )
                 {
                     throw new LuaException( "Arguments must be the same length" );
@@ -292,36 +268,26 @@ public class TermAPI implements ILuaAPI
             case 20:
             {
                 // setPaletteColour/setPaletteColor
-                if(args.length == 2 && args[0] instanceof Double && args[1] instanceof Double)
+                int colour = 15 - parseColour( args );
+                if( args.length == 2 )
                 {
-                    int colour = 15 - parseColour( args );
+                    int hex = getInt( args, 1 );
-                    int hex = ((Double)args[1]).intValue();
                     double[] rgb = Palette.decodeRGB8( hex );
-                    setColour( m_terminal, colour, rgb[0], rgb[1], rgb[2] );
+                    setColour( m_terminal, colour, rgb[ 0 ], rgb[ 1 ], rgb[ 2 ] );
-                    return null;
                 }
-
+                else
-                if(args.length >= 4 && args[0] instanceof Double && args[1] instanceof Double && args[2] instanceof Double && args[3] instanceof Double)
                 {
-                    int colour = 15 - parseColour( args );
+                    double r = getReal( args, 1 );
-                    double r = (Double)args[1];
+                    double g = getReal( args, 2 );
-                    double g = (Double)args[2];
+                    double b = getReal( args, 3 );
-                    double b = (Double)args[3];
                     setColour( m_terminal, colour, r, g, b );
-                    return null;
                 }
-
+                return null;
-                throw new LuaException( "Expected number, number or number, number, number, number" );
             }
             case 21:
             case 22:
             {
                 // getPaletteColour/getPaletteColor
-                if(args.length < 1 || !(args[0] instanceof Double))
-                {
-                    throw new LuaException( "Expected number" );
-                }
-
                 int colour = 15 - parseColour( args );
                 synchronized( m_terminal )
                 {

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

@@ -9,6 +9,8 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.util.Arrays;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getInt;
+
 public class BinaryInputHandle extends HandleGeneric
 {
     private final InputStream m_stream;
@@ -42,13 +44,7 @@ public class BinaryInputHandle extends HandleGeneric
                 {
                     if( args.length > 0 && args[ 0 ] != null )
                     {
-                        if( !(args[ 0 ] instanceof Number) )
+                        int count = getInt( args, 0 );
-                        {
-                            throw new LuaException( "Expected number" );
-                        }
-
-                        int count = ((Number) args[ 0 ]).intValue();
-
                         if( count <= 0 || count >= 1024 * 16 )
                         {
                             throw new LuaException( "Count out of range" );

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

@@ -2,6 +2,7 @@ package dan200.computercraft.core.apis.handles;
 
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.core.apis.ArgumentHelper;
 import dan200.computercraft.shared.util.StringUtil;
 
 import javax.annotation.Nonnull;
@@ -51,7 +52,7 @@ public class BinaryOutputHandle extends HandleGeneric
                     }
                     else
                     {
-                        throw new LuaException( "Expected number" );
+                        throw ArgumentHelper.badArgument( 0, "string or number", args.length > 0 ? args[ 0 ] : null );
                     }
                     return null;
                 }

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

@@ -28,6 +28,9 @@ import javax.annotation.Nonnull;
 import java.util.HashMap;
 import java.util.Map;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getInt;
+import static dan200.computercraft.core.apis.ArgumentHelper.getString;
+
 public class CommandAPI implements ILuaAPI
 {
     private TileCommandComputer m_computer;
@@ -151,11 +154,7 @@ public class CommandAPI implements ILuaAPI
             case 0:
             {
                 // exec
-                if( arguments.length < 1 || !(arguments[0] instanceof String) )
+                final String command = getString( arguments, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                final String command = (String)arguments[0];
                 return context.executeMainThreadTask( new ILuaTask()
                 {
                     @Override
@@ -168,11 +167,7 @@ public class CommandAPI implements ILuaAPI
             case 1:
             {
                 // execAsync
-                if( arguments.length < 1 || !(arguments[0] instanceof String) )
+                final String command = getString( arguments, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-                final String command = (String)arguments[0];
                 long taskID = context.issueMainThreadTask( new ILuaTask()
                 {
                     @Override
@@ -234,22 +229,12 @@ public class CommandAPI implements ILuaAPI
             case 4:
             {
                 // getBlockInfos
-                if( arguments.length < 6 ||
+                final int minx = getInt( arguments, 0 );
-                    !(arguments[0] instanceof Number) ||
+                final int miny = getInt( arguments, 1 );
-                    !(arguments[1] instanceof Number) ||
+                final int minz = getInt( arguments, 2 );
-                    !(arguments[2] instanceof Number) ||
+                final int maxx = getInt( arguments, 3 );
-                    !(arguments[3] instanceof Number) ||
+                final int maxy = getInt( arguments, 4 );
-                    !(arguments[4] instanceof Number) ||
+                final int maxz = getInt( arguments, 5 );
-                    !(arguments[5] instanceof Number) )
-                {
-                    throw new LuaException( "Expected number, number, number, number, number, number" );
-                }
-                final int minx = ((Number)arguments[0]).intValue();
-                final int miny = ((Number)arguments[1]).intValue();
-                final int minz = ((Number)arguments[2]).intValue();
-                final int maxx = ((Number)arguments[3]).intValue();
-                final int maxy = ((Number)arguments[4]).intValue();
-                final int maxz = ((Number)arguments[5]).intValue();
                 return context.executeMainThreadTask( new ILuaTask()
                 {
                     @Override
@@ -295,16 +280,9 @@ public class CommandAPI implements ILuaAPI
             case 5:
             {
                 // getBlockInfo
-                if( arguments.length < 3 ||
+                final int x = getInt( arguments, 0 );
-                        !(arguments[0] instanceof Number) ||
+                final int y = getInt( arguments, 1 );
-                        !(arguments[1] instanceof Number) ||
+                final int z = getInt( arguments, 2 );
-                        !(arguments[2] instanceof Number) )
-                {
-                    throw new LuaException( "Expected number, number, number" );
-                }
-                final int x = ((Number)arguments[0]).intValue();
-                final int y = ((Number)arguments[1]).intValue();
-                final int z = ((Number)arguments[2]).intValue();
                 return context.executeMainThreadTask( new ILuaTask()
                 {
                     @Override

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

@@ -16,6 +16,8 @@ import net.minecraft.util.math.BlockPos;
 
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getString;
+
 public class CommandBlockPeripheral implements IPeripheral
 {
     private final TileEntityCommandBlock m_commandBlock;
@@ -67,12 +69,7 @@ public class CommandBlockPeripheral implements IPeripheral
             case 1:
             {
                 // setCommand
-                if( arguments.length < 1 || !(arguments[0] instanceof String) )
+                final String command = getString( arguments, 0 );
-                {
-                    throw new LuaException( "Expected string" );
-                }
-
-                final String command = (String) arguments[ 0 ];
                 context.issueMainThreadTask( new ILuaTask()
                 {
                     @Override

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

@@ -18,6 +18,8 @@ import net.minecraft.item.ItemStack;
 
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.optString;
+
 public class DiskDrivePeripheral implements IPeripheral
 {
     private final TileDiskDrive m_diskDrive;
@@ -78,15 +80,7 @@ public class DiskDrivePeripheral implements IPeripheral
             case 2:
             {
                 // setDiskLabel
-                String label = null;
+                String label = optString( arguments, 0, null );
-                if( arguments.length > 0 )
-                {
-                    if( arguments[0] != null && !(arguments[0] instanceof String) )
-                    {
-                        throw new LuaException( "Expected string" );
-                    }
-                    label = (String)arguments[0];
-                }
 
                 IMedia media = m_diskDrive.getDiskMedia();
                 if( media != null )

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

@@ -21,6 +21,8 @@ import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getInt;
+
 public abstract class ModemPeripheral
     implements IPeripheral, IPacketSender, IPacketReceiver
 {
@@ -147,11 +149,7 @@ public abstract class ModemPeripheral
     
     private static int parseChannel( Object[] arguments, int index ) throws LuaException
     {
-        if( arguments.length <= index || !(arguments[index] instanceof Double) )
+        int channel = getInt( arguments, index );
-        {
-            throw new LuaException( "Expected number" );
-        }
-        int channel = (int)((Double)arguments[index]).doubleValue();
         if( channel < 0 || channel > 65535 )
         {
             throw new LuaException( "Expected number in range 0-65535" );

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

@@ -40,6 +40,8 @@ import javax.annotation.Nonnull;
 import java.io.File;
 import java.util.*;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getString;
+
 public class TileCable extends TileModemBase
     implements IPacketNetwork
 {
@@ -116,15 +118,6 @@ public class TileCable extends TileModemBase
             return newMethods;
         }
 
-        private String parseString( Object[] arguments, int index ) throws LuaException
-        {
-            if( arguments.length < (index + 1) || !(arguments[index] instanceof String) )
-            {
-                throw new LuaException( "Expected string" );
-            }
-            return (String)arguments[index];
-        }
-
         @Override
         public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaContext context, int method, @Nonnull Object[] arguments ) throws LuaException, InterruptedException
         {
@@ -148,13 +141,13 @@ public class TileCable extends TileModemBase
                 case 1:
                 {
                     // isPresentRemote
-                    String type = m_entity.getTypeRemote( parseString( arguments, 0 ) );
+                    String type = m_entity.getTypeRemote( getString( arguments, 0 ) );
                     return new Object[] { type != null };
                 }
                 case 2:
                 {
                     // getTypeRemote
-                    String type = m_entity.getTypeRemote( parseString( arguments, 0 ) );
+                    String type = m_entity.getTypeRemote( getString( arguments, 0 ) );
                     if( type != null )
                     {
                         return new Object[] { type };
@@ -164,7 +157,7 @@ public class TileCable extends TileModemBase
                 case 3:
                 {
                     // getMethodsRemote
-                    String[] methodNames = m_entity.getMethodNamesRemote( parseString( arguments, 0 ) );
+                    String[] methodNames = m_entity.getMethodNamesRemote( getString( arguments, 0 ) );
                     if( methodNames != null )
                     {
                         Map<Object,Object> table = new HashMap<Object,Object>();
@@ -178,8 +171,8 @@ public class TileCable extends TileModemBase
                 case 4:
                 {
                     // callRemote
-                    String remoteName = parseString( arguments, 0 );
+                    String remoteName = getString( arguments, 0 );
-                    String methodName = parseString( arguments, 1 );
+                    String methodName = getString( arguments, 1 );
                     Object[] methodArgs = new Object[ arguments.length - 2 ];
                     System.arraycopy( arguments, 2, methodArgs, 0, arguments.length - 2 );
                     return m_entity.callMethodRemote( remoteName, context, methodName, methodArgs );

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

@@ -10,14 +10,15 @@ import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
+import dan200.computercraft.core.apis.TermAPI;
 import dan200.computercraft.core.terminal.Terminal;
 import dan200.computercraft.shared.util.Palette;
 import org.apache.commons.lang3.ArrayUtils;
 
-import java.util.HashMap;
-
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.*;
+
 public class MonitorPeripheral implements IPeripheral
 {
     private final TileMonitor m_monitor;
@@ -90,23 +91,16 @@ public class MonitorPeripheral implements IPeripheral
             case 1:
             {
                 // scroll
-                if( args.length < 1 || !(args[0] instanceof Number) )
+                int value = getInt( args, 0 );
-                {
-                    throw new LuaException( "Expected number" );
-                }
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
-                terminal.scroll( ((Number)(args[0])).intValue() );
+                terminal.scroll( value );
                 return null;
             }
             case 2:
             {
                 // setCursorPos
-                if( args.length < 2 || !(args[0] instanceof Number) || !(args[1] instanceof Number) )
+                int x = getInt( args, 0 ) - 1;
-                {
+                int y = getInt( args, 1 ) - 1;
-                    throw new LuaException( "Expected number, number" );
-                }
-                int x = ((Number)args[0]).intValue() - 1;
-                int y = ((Number)args[1]).intValue() - 1;
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
                 terminal.setCursorPos( x, y );
                 return null;
@@ -114,12 +108,9 @@ public class MonitorPeripheral implements IPeripheral
             case 3:
             {
                 // setCursorBlink
-                if( args.length < 1 || !(args[0] instanceof Boolean) )
+                boolean blink = getBoolean( args, 0 );
-                {
-                    throw new LuaException( "Expected boolean" );
-                }
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
-                terminal.setCursorBlink( (Boolean) args[ 0 ] );
+                terminal.setCursorBlink( blink );
                 return null;
             }
             case 4:
@@ -157,11 +148,7 @@ public class MonitorPeripheral implements IPeripheral
             case 8:
             {
                 // setTextScale
-                if( args.length < 1 || !(args[0] instanceof Number) )
+                int scale = (int) (getReal( args, 0 ) * 2.0);
-                {
-                    throw new LuaException( "Expected number" );
-                }
-                int scale = (int)(((Number)args[0]).doubleValue() * 2.0);
                 if( scale < 1 || scale > 10 )
                 {
                     throw new LuaException( "Expected number in range 0.5-5" );
@@ -173,7 +160,7 @@ public class MonitorPeripheral implements IPeripheral
             case 10:
             {
                 // setTextColour/setTextColor
-                int colour = dan200.computercraft.core.apis.TermAPI.parseColour( args );
+                int colour = TermAPI.parseColour( args );
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
                 terminal.setTextColour( colour );
                 return null;
@@ -182,7 +169,7 @@ public class MonitorPeripheral implements IPeripheral
             case 12:
             {
                 // setBackgroundColour/setBackgroundColor
-                int colour = dan200.computercraft.core.apis.TermAPI.parseColour( args );
+                int colour = TermAPI.parseColour( args );
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
                 terminal.setBackgroundColour( colour );
                 return null;
@@ -200,26 +187,21 @@ public class MonitorPeripheral implements IPeripheral
             {
                 // getTextColour/getTextColor
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
-                return dan200.computercraft.core.apis.TermAPI.encodeColour( terminal.getTextColour() );
+                return TermAPI.encodeColour( terminal.getTextColour() );
             }
             case 17:
             case 18:
             {
                 // getBackgroundColour/getBackgroundColor
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
-                return dan200.computercraft.core.apis.TermAPI.encodeColour( terminal.getBackgroundColour() );
+                return TermAPI.encodeColour( terminal.getBackgroundColour() );
             }
             case 19:
             {
                 // blit
-                if( args.length < 3 || !(args[0] instanceof String) || !(args[1] instanceof String) || !(args[2] instanceof String) )
+                String text = getString( args, 0 );
-                {
+                String textColour = getString( args, 1 );
-                    throw new LuaException( "Expected string, string, string" );
+                String backgroundColour = getString( args, 2 );
-                }
-
-                String text = (String)args[0];
-                String textColour = (String)args[1];
-                String backgroundColour = (String)args[2];
                 if( textColour.length() != text.length() || backgroundColour.length() != text.length() )
                 {
                     throw new LuaException( "Arguments must be the same length" );
@@ -236,26 +218,21 @@ public class MonitorPeripheral implements IPeripheral
                 // setPaletteColour/setPaletteColor
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
 
-                if(args.length == 2 && args[0] instanceof Double && args[1] instanceof Double)
+                int colour = 15 - TermAPI.parseColour( args );
+                if( args.length == 2 )
                 {
-                    int colour = 15 - dan200.computercraft.core.apis.TermAPI.parseColour( args );
+                    int hex = getInt( args, 1 );
-                    int hex = ((Double)args[1]).intValue();
                     double[] rgb = Palette.decodeRGB8( hex );
-                    dan200.computercraft.core.apis.TermAPI.setColour( terminal, colour, rgb[0], rgb[1], rgb[2] );
+                    TermAPI.setColour( terminal, colour, rgb[ 0 ], rgb[ 1 ], rgb[ 2 ] );
-                    return null;
                 }
-
+                else
-                if (args.length >= 4 && args[0] instanceof Double && args[1] instanceof Double && args[2] instanceof Double && args[3] instanceof Double)
                 {
-                    int colour = 15 - dan200.computercraft.core.apis.TermAPI.parseColour( args );
+                    double r = getReal( args, 1 );
-                    double r = (Double)args[1];
+                    double g = getReal( args, 2 );
-                    double g = (Double)args[2];
+                    double b = getReal( args, 3 );
-                    double b = (Double)args[3];
+                    TermAPI.setColour( terminal, colour, r, g, b );
-                    dan200.computercraft.core.apis.TermAPI.setColour( terminal, colour, r, g, b );
-                    return null;
                 }
-
+                return null;
-                throw new LuaException( "Expected number, number, number, number" );
             }
             case 22:
             case 23:
@@ -264,7 +241,7 @@ public class MonitorPeripheral implements IPeripheral
                 Terminal terminal = m_monitor.getTerminal().getTerminal();
                 Palette palette = terminal.getPalette();
 
-                int colour = 15 - dan200.computercraft.core.apis.TermAPI.parseColour( args );
+                int colour = 15 - TermAPI.parseColour( args );
 
                 if( palette != null )
                 {

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

@@ -14,6 +14,9 @@ import dan200.computercraft.core.terminal.Terminal;
 
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getInt;
+import static dan200.computercraft.core.apis.ArgumentHelper.optString;
+
 public class PrinterPeripheral implements IPeripheral
 {
     private final TilePrinter m_printer;
@@ -70,13 +73,8 @@ public class PrinterPeripheral implements IPeripheral
             case 1:
             {
                 // setCursorPos
-                if( args.length != 2 || args[0] == null || !(args[0] instanceof Number) || args[1] == null || !(args[1] instanceof Number) )
+                int x = getInt( args, 0 ) - 1;
-                {
+                int y = getInt( args, 1 ) - 1;
-                    throw new LuaException( "Expected number, number" );
-                }
-
-                int x = ((Number)args[0]).intValue() - 1;
-                int y = ((Number)args[1]).intValue() - 1;
                 Terminal page = getCurrentPage();
                 page.setCursorPos( x, y );
                 return null;
@@ -116,16 +114,7 @@ public class PrinterPeripheral implements IPeripheral
             case 7:
             {
                 // setPageTitle
-                String title = "";
+                String title = optString( args, 0, "" );
-                if( args.length > 0 && args[0] != null )
-                {
-                    if( !(args[0] instanceof String) )
-                    {
-                        throw new LuaException( "Expected string" );
-                    }
-                    title = (String)args[0];
-                }
-
                 getCurrentPage();
                 m_printer.setPageTitle( title );
                 return null;

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

@@ -17,9 +17,13 @@ import net.minecraft.util.SoundCategory;
 import net.minecraft.util.SoundEvent;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
+
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.getString;
+import static dan200.computercraft.core.apis.ArgumentHelper.optReal;
+
 public class SpeakerPeripheral implements IPeripheral {
     private TileSpeaker m_speaker;
     private long m_clock;
@@ -127,47 +131,20 @@ public class SpeakerPeripheral implements IPeripheral {
     @Nonnull
     private synchronized Object[] playNote( Object[] arguments, ILuaContext context ) throws LuaException
     {
-        float volume = 1.0f;
+        String name = getString(arguments, 0);
-        float pitch = 1.0f;
+        float volume = (float) optReal( arguments, 1, 1.0 );
+        float pitch = (float) optReal( arguments, 2, 1.0 );
 
-        // Check if arguments are correct
+        // Check if sound exists
-        if( arguments.length == 0 ) // Too few args
+        if ( !SoundEvent.REGISTRY.containsKey( new ResourceLocation( "block.note." + name ) ) )
-        {
-            throw new LuaException( "Expected string, number (optional), number (optional)" );
-        }
-
-        if( !(arguments[0] instanceof String) ) // Arg wrong type
-        {
-            throw new LuaException("Expected string, number (optional), number (optional)");
-        }
-
-        if ( !SoundEvent.REGISTRY.containsKey( new ResourceLocation( "block.note." + arguments[0] ) ) )
         {
             throw new LuaException("Invalid instrument, \"" + arguments[0] + "\"!");
         }
 
-        if ( arguments.length > 1 )
-        {
-            if ( arguments[1] != null && !(arguments[1] instanceof Double) )   // Arg wrong type
-            {
-                throw new LuaException( "Expected string, number (optional), number (optional)" );
-            }
-            volume = arguments[1] != null ? ((Double) arguments[1]).floatValue() : 1f;
-        }
-
-        if( arguments.length > 2 )
-        {
-            if( arguments[2] != null && !(arguments[2] instanceof Double) )  // Arg wrong type
-            {
-                throw new LuaException("Expected string, number (optional), number (optional)");
-            }
-            pitch = arguments[2] != null ? ((Double) arguments[2]).floatValue() : 1f;
-        }
-
         // If the resource location for note block notes changes, this method call will need to be updated
         Object[] returnValue = playSound(
             new Object[] {
-                "block.note." + arguments[0],
+                "block.note." + name,
                 (double)Math.min( volume, 3f ),
                 Math.pow( 2.0f, ( pitch - 12.0f ) / 12.0f)
             }, context, true
@@ -184,42 +161,11 @@ public class SpeakerPeripheral implements IPeripheral {
     @Nonnull
     private synchronized Object[] playSound( Object[] arguments, ILuaContext context, boolean isNote ) throws LuaException
     {
+        String name = getString(arguments, 0);
+        float volume = (float) optReal( arguments, 1, 1.0 );
+        float pitch = (float) optReal( arguments, 2, 1.0 );
 
-        float volume = 1.0f;
+        ResourceLocation resourceName = new ResourceLocation( name );
-        float pitch = 1.0f;
-
-        // Check if arguments are correct
-        if( arguments.length == 0 ) // Too few args
-        {
-            throw new LuaException( "Expected string, number (optional), number (optional)" );
-        }
-
-        if( !(arguments[0] instanceof String) ) // Arg wrong type
-        {
-            throw new LuaException( "Expected string, number (optional), number (optional)" );
-        }
-
-        if( arguments.length > 1 )
-        {
-            if( arguments[1] != null && !(arguments[1] instanceof Double) )  // Arg wrong type
-            {
-                throw new LuaException( "Expected string, number (optional), number (optional)" );
-            }
-
-            volume = arguments[1] != null ? ((Double) arguments[1]).floatValue() : 1f;
-
-        }
-
-        if( arguments.length > 2 )
-        {
-            if( arguments[2] != null && !(arguments[2] instanceof Double) )  // Arg wrong type
-            {
-                throw new LuaException( "Expected string, number (optional), number (optional)" );
-            }
-            pitch = arguments[2] != null ? ((Double) arguments[2]).floatValue() : 1f;
-        }
-
-        ResourceLocation resourceName = new ResourceLocation( (String) arguments[0] );
 
         if( m_clock - m_lastPlayTime >= TileSpeaker.MIN_TICKS_BETWEEN_SOUNDS || ( ( m_clock - m_lastPlayTime == 0 ) && ( m_notesThisTick < ComputerCraft.maxNotesPerTick ) && isNote ) )
         {

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

@@ -22,6 +22,8 @@ import javax.annotation.Nonnull;
 import java.util.HashMap;
 import java.util.Map;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.*;
+
 public class TurtleAPI implements ILuaAPI
 {
     private IAPIEnvironment m_environment;
@@ -115,38 +117,23 @@ public class TurtleAPI implements ILuaAPI
 
     private int parseSlotNumber( Object[] arguments, int index ) throws LuaException
     {
-        int slot = parseOptionalSlotNumber( arguments, index, 99 );
+        int slot = getInt( arguments, index );
-        if( slot == 99 )
+        if( slot < 1 || slot > 16 ) throw new LuaException( "Slot number " + slot + " out of range" );
-        {
+        return slot - 1;
-            throw new LuaException( "Expected number" );
-        }
-        return slot;
     }
 
     private int parseOptionalSlotNumber( Object[] arguments, int index, int fallback ) throws LuaException
     {
-        if( arguments.length <= index || !(arguments[index] instanceof Number) )
+        if( index >= arguments.length || arguments[ index ] == null ) return fallback;
-        {
+
-            return fallback;
+        int slot = getInt( arguments, index );
-        }
+        if( slot < 1 || slot > 16 ) throw new LuaException( "Slot number " + slot + " out of range" );
-        int slot = ((Number)arguments[index]).intValue();
+        return slot - 1;
-        if( slot >= 1 && slot <= 16 )
-        {
-            return slot - 1;
-        }
-        else
-        {
-            throw new LuaException( "Slot number " + slot + " out of range" );
-        }
     }
     
     private int parseCount( Object[] arguments, int index ) throws LuaException
     {
-        if( arguments.length <= index || !(arguments[index] instanceof Number) )
+        int count = optInt( arguments, index, 64 );
-        {
-            throw new LuaException( "Expected number" );
-        }
-        int count = ((Number)arguments[index]).intValue();
         if( count >= 0 && count <= 64 )
         {
             return count;
@@ -159,19 +146,16 @@ public class TurtleAPI implements ILuaAPI
 
     private Optional<TurtleSide> parseSide( Object[] arguments, int index ) throws LuaException
     {
-        if( arguments.length <= index || arguments[index] == null )
+        String side = optString( arguments, index, null );
+        if( side == null )
         {
             return Optional.absent();
         }
-        if( !(arguments[ index ] instanceof String) )
+        else if( side.equalsIgnoreCase( "left" ) )
-        {
-            throw new LuaException( "Expected string" );
-        }
-        if( arguments[ index ].equals( "left" ) )
         {
             return Optional.of( TurtleSide.Left );
         }
-        else if( arguments[ index ].equals( "right" ) )
+        else if( side.equalsIgnoreCase( "right" ) )
         {
             return Optional.of( TurtleSide.Right );
         }
@@ -252,11 +236,7 @@ public class TurtleAPI implements ILuaAPI
             case 12:
             {
                 // drop
-                int count = 64;
+                int count = parseCount( args, 0 );
-                if( args.length > 0 )
-                {
-                    count = parseCount( args, 0 );
-                }
                 return tryCommand( context, new TurtleDropCommand( InteractDirection.Forward, count ) );
             }
             case 13:
@@ -343,51 +323,31 @@ public class TurtleAPI implements ILuaAPI
             case 25:
             {
                 // dropUp
-                int count = 64;
+                int count = parseCount( args, 0 );
-                if( args.length > 0 )
-                {
-                    count = parseCount( args, 0 );
-                }
                 return tryCommand( context, new TurtleDropCommand( InteractDirection.Up, count ) );
             }
             case 26:
             {
                 // dropDown
-                int count = 64;
+                int count = parseCount( args, 0 );
-                if( args.length > 0 )
-                {
-                    count = parseCount( args, 0 );
-                }
                 return tryCommand( context, new TurtleDropCommand( InteractDirection.Down, count ) );
             }
             case 27:
             {
                 // suck
-                int count = 64;
+                int count = parseCount( args, 0 );
-                if( args.length > 0 )
-                {
-                    count = parseCount( args, 0 );
-                }
                 return tryCommand( context, new TurtleSuckCommand( InteractDirection.Forward, count ) );
             }
             case 28:
             {
                 // suckUp
-                int count = 64;
+                int count = parseCount( args, 0 );
-                if( args.length > 0 )
-                {
-                    count = parseCount( args, 0 );
-                }
                 return tryCommand( context, new TurtleSuckCommand( InteractDirection.Up, count ) );
             }
             case 29:
             {
                 // suckDown
-                int count = 64;
+                int count = parseCount( args, 0 );
-                if( args.length > 0 )
-                {
-                    count = parseCount( args, 0 );
-                }
                 return tryCommand( context, new TurtleSuckCommand( InteractDirection.Down, count ) );
             }
             case 30:
@@ -405,11 +365,7 @@ public class TurtleAPI implements ILuaAPI
             case 31:
             {
                 // refuel
-                int count = 64;
+                int count = parseCount( args, 0 );
-                if( args.length > 0 )
-                {
-                    count = parseCount( args, 0 );
-                }
                 return tryCommand( context, new TurtleRefuelCommand( count ) );
             }
             case 32:
@@ -422,11 +378,7 @@ public class TurtleAPI implements ILuaAPI
             {
                 // transferTo
                 int slot = parseSlotNumber( args, 0 );
-                int count = 64;
+                int count = parseCount( args, 1 );
-                if( args.length > 1 )
-                {
-                    count = parseCount( args, 1 );
-                }
                 return tryCommand( context, new TurtleTransferToCommand( slot, count ) );
             }
             case 34:

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

@@ -15,6 +15,8 @@ import dan200.computercraft.shared.turtle.core.TurtleCraftCommand;
 
 import javax.annotation.Nonnull;
 
+import static dan200.computercraft.core.apis.ArgumentHelper.optInt;
+
 public class CraftingTablePeripheral
     implements IPeripheral
 {
@@ -45,16 +47,7 @@ public class CraftingTablePeripheral
         
     private int parseCount( Object[] arguments ) throws LuaException
     {
-        if( arguments.length < 1 )
+        int count = optInt( arguments, 0, 64 );
-        {
-            return 64;
-        }
-        
-        if( !(arguments[0] instanceof Number) )
-        {
-            throw new LuaException( "Expected number" );
-        }
-        int count = ((Number)arguments[0]).intValue();
         if( count < 0 || count > 64 )
         {
             throw new LuaException( "Crafting count " + count + " out of range" );