diff --git a/Makefile b/Makefile
index 5d623346..8f4e88b4 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ TARGET=interp
 PREFIX=/usr/local
 
 # C sources
-HEADERS=vm.h ds.h compile.h parse.h value.h datatypes.h gc.h util.h
+HEADERS=vm.h ds.h compile.h parse.h value.h datatypes.h gc.h util.h gst.h
 SOURCES=main.c parse.c value.c vm.c ds.c compile.c gc.c
 OBJECTS=$(patsubst %.c,%.o,$(SOURCES))
 
diff --git a/compile.h b/compile.h
index 4b2f3d6c..0736b490 100644
--- a/compile.h
+++ b/compile.h
@@ -2,6 +2,20 @@
 #define COMPILE_H_9VXF71HY
 
 #include "datatypes.h"
+#include <setjmp.h>
+
+typedef struct GstCompiler GstCompiler;
+typedef struct GstScope GstScope;
+
+/* Compilation state */
+struct GstCompiler {
+    Gst *vm;
+    const char *error;
+    jmp_buf onError;
+    GstScope *tail;
+    GstArray *env;
+    GstBuffer *buffer;
+};
 
 /* Initialize the Compiler */
 void gst_compiler(GstCompiler *c, Gst *vm);
@@ -15,10 +29,4 @@ void gst_compiler_add_global_cfunction(GstCompiler *c, const char *name, GstCFun
 /* Compile a function that evaluates the given form. */
 GstFunction *gst_compiler_compile(GstCompiler *c, GstValue form);
 
-/* Macro expansion. Macro expansion happens prior to the compilation process
- * and is completely separate. This allows the compilation to not have to worry
- * about garbage collection and other issues that would complicate both the
- * runtime and the compilation. */
-int gst_macro_expand(Gst *vm, GstValue x, GstObject *macros, GstValue *out);
-
 #endif /* end of include guard: COMPILE_H_9VXF71HY */
diff --git a/datatypes.h b/datatypes.h
index 9445a8e1..3c1bf815 100644
--- a/datatypes.h
+++ b/datatypes.h
@@ -2,7 +2,6 @@
 #define DATATYPES_H_PJJ035NT
 
 #include <stdint.h>
-#include <setjmp.h>
 
 /* Flag for immutability in an otherwise mutable datastructure */
 #define GST_IMMUTABLE 1
@@ -36,19 +35,15 @@ typedef struct GstArray GstArray;
 typedef struct GstBuffer GstBuffer;
 typedef struct GstObject GstObject;
 typedef struct GstThread GstThread;
-typedef GstValue (*GstCFunction)(Gst * vm);
+typedef int (*GstCFunction)(Gst * vm);
 
 /* Implementation details */
-typedef struct GstParser GstParser;
-typedef struct GstCompiler GstCompiler;
 typedef struct GstFuncDef GstFuncDef;
 typedef struct GstFuncEnv GstFuncEnv;
 
 /* Definitely implementation details */
 typedef struct GstStackFrame GstStackFrame;
-typedef struct GstParseState GstParseState;
 typedef struct GstBucket GstBucket;
-typedef struct GstScope GstScope;
 
 /* The general gst value type. Contains a large union and
  * the type information of the value */
@@ -155,6 +150,11 @@ struct GstStackFrame {
     uint16_t *pc;
 };
 
+/* VM return status from c function */
+#define GST_RETURN_OK 0
+#define GST_RETURN_ERROR 1
+#define GST_RETURN_CRASH 2
+
 /* The VM state */
 struct Gst {
     /* Garbage collection */
@@ -166,47 +166,9 @@ struct Gst {
     GstThread *thread;
     /* Return state */
     const char *crash;
-    jmp_buf jump;
-    GstValue error;
-    GstValue ret; /* Returned value from VMStart. Also holds errors. */
+    GstValue ret; /* Returned value from gst_start. Also holds errors. */
 };
 
-struct GstParser {
-    Gst *vm;
-    const char *error;
-    GstParseState *data;
-    GstValue value;
-    uint32_t count;
-    uint32_t cap;
-    uint32_t index;
-    uint32_t flags;
-    enum {
-		GST_PARSER_PENDING = 0,
-		GST_PARSER_FULL,
-		GST_PARSER_ERROR
-    } status;
-};
-
-/* Compilation state */
-struct GstCompiler {
-    Gst *vm;
-    const char *error;
-    jmp_buf onError;
-    GstScope *tail;
-    GstArray *env;
-    GstBuffer *buffer;
-};
-
-/* String utils */
-#define gst_string_raw(s) ((uint32_t *)(s) - 2)
-#define gst_string_length(v) (gst_string_raw(v)[0])
-#define gst_string_hash(v) (gst_string_raw(v)[1])
-
-/* Tuple utils */
-#define gst_tuple_raw(s) ((uint32_t *)(s) - 2)
-#define gst_tuple_length(v) (gst_tuple_raw(v)[0])
-#define gst_tuple_hash(v) (gst_tuple_raw(v)[1])
-
 /* Bytecode */
 enum GstOpCode {
     GST_OP_ADD = 0, /* Addition */
diff --git a/gc.c b/gc.c
index b029df16..582388c7 100644
--- a/gc.c
+++ b/gc.c
@@ -184,7 +184,7 @@ void gst_sweep(Gst *vm) {
 static void *gst_alloc_prepare(Gst *vm, char *rawBlock, uint32_t size) {
     GCMemoryHeader *mdata;
     if (rawBlock == NULL) {
-        gst_crash(vm, "out of memory");
+        GST_OUT_OF_MEMORY;
     }
     vm->nextCollection += size;
     mdata = (GCMemoryHeader *)rawBlock;
@@ -216,7 +216,6 @@ void gst_collect(Gst *vm) {
         gst_mark(vm, &thread);
     }
     gst_mark(vm, &vm->ret);
-    gst_mark(vm, &vm->error);
     gst_sweep(vm);
     vm->nextCollection = 0;
 }
diff --git a/gst.h b/gst.h
new file mode 100644
index 00000000..eeb9c4fc
--- /dev/null
+++ b/gst.h
@@ -0,0 +1,12 @@
+#ifndef gst_h_INCLUDED
+#define gst_h_INCLUDED
+
+#include "util.h"
+#include "datatypes.h"
+#include "vm.h"
+#include "parse.h"
+#include "compile.h"
+#include "value.h"
+
+#endif // gst_h_INCLUDED
+
diff --git a/main.c b/main.c
index ced00d59..2f54bb9e 100644
--- a/main.c
+++ b/main.c
@@ -1,10 +1,6 @@
 #include <stdlib.h>
 #include <stdio.h>
-#include "datatypes.h"
-#include "vm.h"
-#include "parse.h"
-#include "compile.h"
-#include "value.h"
+#include "gst.h"
 
 /* Simple printer for gst strings */
 void string_put(FILE *out, uint8_t * string) {
@@ -15,16 +11,14 @@ void string_put(FILE *out, uint8_t * string) {
 }
 
 /* Test c function */
-GstValue print(Gst *vm) {
+int print(Gst *vm) {
     uint32_t j, count;
-    GstValue nil;
     count = gst_count_args(vm);
     for (j = 0; j < count; ++j) {
         string_put(stdout, gst_to_string(vm, gst_arg(vm, j)));
         fputc('\n', stdout);
     }
-    nil.type = GST_NIL;
-    return nil;
+    return GST_RETURN_OK;
 }
 
 /* A simple repl for debugging */
@@ -98,7 +92,7 @@ void debug_repl(FILE *in, FILE *out) {
                     fprintf(out, "VM crash: %s\n", vm.crash);
                 } else {
                     fprintf(out, "VM error: ");
-                    string_put(out, gst_to_string(&vm, vm.error));
+                    string_put(out, gst_to_string(&vm, vm.ret));
                     printf("\n");
                 }
             }
diff --git a/parse.h b/parse.h
index 2a9ac2bd..fcdf0e8a 100644
--- a/parse.h
+++ b/parse.h
@@ -3,6 +3,26 @@
 
 #include "datatypes.h"
 
+typedef struct GstParser GstParser;
+typedef struct GstParseState GstParseState;
+
+/* Holds the parsing state */
+struct GstParser {
+    Gst *vm;
+    const char *error;
+    GstParseState *data;
+    GstValue value;
+    uint32_t count;
+    uint32_t cap;
+    uint32_t index;
+    uint32_t flags;
+    enum {
+		GST_PARSER_PENDING = 0,
+		GST_PARSER_FULL,
+		GST_PARSER_ERROR
+    } status;
+};
+
 /* Some parser flags */
 #define GST_PARSER_FLAG_INCOMMENT 1
 #define GST_PARSER_FLAG_EXPECTING_COMMENT 2
diff --git a/util.h b/util.h
index c22ae2be..2e50473c 100644
--- a/util.h
+++ b/util.h
@@ -1,6 +1,16 @@
 #ifndef util_h_INCLUDED
 #define util_h_INCLUDED
 
+/* String utils */
+#define gst_string_raw(s) ((uint32_t *)(s) - 2)
+#define gst_string_length(v) (gst_string_raw(v)[0])
+#define gst_string_hash(v) (gst_string_raw(v)[1])
+
+/* Tuple utils */
+#define gst_tuple_raw(s) ((uint32_t *)(s) - 2)
+#define gst_tuple_length(v) (gst_tuple_raw(v)[0])
+#define gst_tuple_hash(v) (gst_tuple_raw(v)[1])
+
 /* Memcpy for moving memory */
 #ifndef gst_memcpy
 #include <string.h>
@@ -36,5 +46,20 @@
 #define NULL ((void *)0)
 #endif
 
+/* C function helpers */
+
+/* Return in a c function */
+#define gst_c_return(vm, x) (do { (vm)->ret = (x); return GST_RETURN_OK; } while (0))
+
+/* Throw error from a c function */
+#define gst_c_throw(vm, e) (do { (vm)->ret = (e); return GST_RETURN_ERROR; } while (0))
+
+/* What to do when out of memory */
+#ifndef GST_OUT_OF_MEMORY
+#include <stdlib.h>
+#include <stdio.h>
+#define GST_OUT_OF_MEMORY do { printf("out of memory.\n"); exit(1); } while (0)
+#endif
+
 #endif // util_h_INCLUDED
 
diff --git a/value.c b/value.c
index 3bb7a9f1..b07279a9 100644
--- a/value.c
+++ b/value.c
@@ -388,75 +388,78 @@ static uint8_t to_byte(GstNumber raw) {
 	return (uint8_t) raw;
 }
 
-/* Get a value out af an associated data structure. Can throw VM error. */
-GstValue gst_get(Gst *vm, GstValue ds, GstValue key) {
+/* Get a value out af an associated data structure. 
+ * Returns possible c error message, and NULL for no error. The
+ * useful return value is written to out on success */
+const char *gst_get(GstValue ds, GstValue key, GstValue *out) {
     int32_t index;
     GstValue ret;
 	switch (ds.type) {
 	case GST_ARRAY:
-       	gst_assert_type(vm, key, GST_NUMBER);
+        if (key.type != GST_NUMBER) return "expected numeric key";
 		index = to_index(key.data.number, ds.data.array->count);
-		if (index == -1) gst_error(vm, "invalid array access");
+		if (index == -1) return "invalid array access";
 		ret = ds.data.array->data[index];
 		break;
 	case GST_TUPLE:
-       	gst_assert_type(vm, key, GST_NUMBER);
+        if (key.type != GST_NUMBER) return "expected numeric key";
 		index = to_index(key.data.number, gst_tuple_length(ds.data.tuple));
-		if (index < 0) gst_error(vm, "invalid tuple access");
+		if (index < 0) return "invalid tuple access";
 		ret = ds.data.tuple[index];
 		break;
     case GST_BYTEBUFFER:
-        gst_assert_type(vm, key, GST_NUMBER);
+        if (key.type != GST_NUMBER) return "expected numeric key";
         index = to_index(key.data.number, ds.data.buffer->count);
-		if (index == -1) gst_error(vm, "invalid buffer access");
+		if (index == -1) return "invalid buffer access";
 		ret.type = GST_NUMBER;
 		ret.data.number = ds.data.buffer->data[index];
 		break;
     case GST_STRING:
-        gst_assert_type(vm, key, GST_NUMBER);
+        if (key.type != GST_NUMBER) return "expected numeric key";
         index = to_index(key.data.number, gst_string_length(ds.data.string));
-		if (index == -1) gst_error(vm, "invalid string access");
+		if (index == -1) return "invalid string access";
 		ret.type = GST_NUMBER;
 		ret.data.number = ds.data.string[index];
 		break;
     case GST_OBJECT:
-        return gst_object_get(ds.data.object, key);
+       	ret = gst_object_get(ds.data.object, key);
+       	break;
     default:
-        gst_error(vm, "cannot get");
+       return "cannot get";
 	}
-	return ret;
+	*out = ret;
+	return NULL;
 }
 
-/* Set a value in an associative data structure. Can throw VM error. */
-void gst_set(Gst *vm, GstValue ds, GstValue key, GstValue value) {
+/* Set a value in an associative data structure. Returns possible
+ * error message, and NULL if no error. */
+const char *gst_set(Gst *vm, GstValue ds, GstValue key, GstValue value) {
     int32_t index;
 	switch (ds.type) {
 	case GST_ARRAY:
         if (ds.data.array->flags & GST_IMMUTABLE)
-            goto immutable;
-       	gst_assert_type(vm, key, GST_NUMBER);
+            return "cannot set immutable value";
+        if (key.type != GST_NUMBER) return "expected numeric key";
 		index = to_index(key.data.number, ds.data.array->count);
-		if (index == -1) gst_error(vm, "invalid array access");
+		if (index == -1) return "invalid array access";
 		ds.data.array->data[index] = value;
 		break;
     case GST_BYTEBUFFER:
         if (ds.data.buffer->flags & GST_IMMUTABLE)
-            goto immutable;
-        gst_assert_type(vm, key, GST_NUMBER);
-        gst_assert_type(vm, value, GST_NUMBER);
+            return "cannot set immutable value";
+        if (key.type != GST_NUMBER) return "expected numeric key";
+        if (value.type != GST_NUMBER) return "expected numeric value";
         index = to_index(key.data.number, ds.data.buffer->count);
-		if (index == -1) gst_error(vm, "invalid buffer access");
+		if (index == -1) return "invalid buffer access";
 		ds.data.buffer->data[index] = to_byte(value.data.number);
 		break;
     case GST_OBJECT:
         if (ds.data.object->flags & GST_IMMUTABLE)
-            goto immutable;
+            return "cannot set immutable value";
         gst_object_put(vm, ds.data.object, key, value);
         break;
     default:
-        gst_error(vm, "cannot set");
+    	return "cannot set";
 	}
-	return;
-    immutable:
-        gst_error(vm, "cannot set immutable value");
+	return NULL;
 }
diff --git a/value.h b/value.h
index cb90554f..8595870c 100644
--- a/value.h
+++ b/value.h
@@ -15,10 +15,10 @@ int gst_compare(GstValue x, GstValue y);
 int gst_equals(GstValue x, GstValue y);
 
 /* Get a value from an associative gst object. Can throw errors. */
-GstValue gst_get(Gst *vm, GstValue ds, GstValue key);
+const char *gst_get(GstValue ds, GstValue key, GstValue *out);
 
 /* Set a value in an associative gst object. Can throw errors. */
-void gst_set(Gst *vm, GstValue ds, GstValue key, GstValue value);
+const char *gst_set(Gst *vm, GstValue ds, GstValue key, GstValue value);
 
 /* Load a c style string into a gst value (copies data) */
 GstValue gst_load_cstring(Gst *vm, const char *string);
diff --git a/vm.c b/vm.c
index 02661fae..dce4ff18 100644
--- a/vm.c
+++ b/vm.c
@@ -1,23 +1,28 @@
-
 #include "vm.h"
 #include "util.h"
 #include "value.h"
 #include "ds.h"
 #include "gc.h"
 
+/* Macros for errors in the vm */
+
+/* Exit from the VM normally */
+#define gst_exit(vm, r) return ((vm)->ret = (r), GST_RETURN_OK)
+
+/* Bail from the VM with an error string. */
+#define gst_error(vm, e) return ((vm)->ret = gst_load_cstring((vm), (e)), GST_RETURN_ERROR)
+
+/* Crash. Not catchable, unlike error. */
+#define gst_crash(vm, e) return ((vm)->crash = (e), GST_RETURN_CRASH)
+
+/* Error if the condition is false */
+#define gst_assert(vm, cond, e) do {if (!(cond)){gst_error((vm), (e));}} while (0)
+
 static const char GST_NO_UPVALUE[] = "no upvalue";
 static const char GST_EXPECTED_FUNCTION[] = "expected function";
 static const char GST_EXPECTED_NUMBER_ROP[] = "expected right operand to be number";
 static const char GST_EXPECTED_NUMBER_LOP[] = "expected left operand to be number";
 
-/* Get a literal */
-static GstValue gst_vm_literal(Gst *vm, GstFunction *fn, uint16_t index) {
-    if (index > fn->def->literalsLen) {
-        gst_error(vm, GST_NO_UPVALUE);
-    }
-    return fn->def->literals[index];
-}
-
 /* Load a function into the VM. The function will be called with
  * no arguments when run */
 static void gst_load(Gst *vm, GstValue callee) {
@@ -61,53 +66,18 @@ int gst_start(Gst *vm, GstValue func) {
     GstStackFrame frame;
     GstValue temp, v1, v2;
     uint16_t *pc;
+
 	/* Load the callee */
 	gst_load(vm, func);
+
+	/* Intialize local state */
 	thread = *vm->thread;
     stack = thread.data + thread.count;
     frame = *((GstStackFrame *)(stack - GST_FRAME_SIZE));
     pc = frame.pc;
 
-    /* Set jmp_buf to jump back to for return. */
-    {
-        int n;
-        if ((n = setjmp(vm->jump))) {
-            /* Good return */
-            if (n == 1) {
-                return 0;
-            } else if (n == 2) {
-                /* Error. */
-                while (!frame.errorJump) {
-                    /* Check for closure */
-                    if (frame.env) {
-                        frame.env->thread = NULL;
-                        frame.env->stackOffset = frame.size;
-                        frame.env->values = gst_alloc(vm, sizeof(GstValue) * frame.size);
-                        gst_memcpy(frame.env->values, 
-                            thread.data + thread.count, 
-                            frame.size * sizeof(GstValue));
-                    }
-                    stack -= frame.prevSize + GST_FRAME_SIZE;
-                    if (stack <= thread.data) {
-                        thread.count = 0;
-                        break;
-                    }
-                    frame = *((GstStackFrame *)(stack - GST_FRAME_SIZE));
-                }
-                if (thread.count < GST_FRAME_SIZE)
-                    return n;
-                /* Jump to the error location */
-                pc = frame.errorJump;
-                /* Set error */
-                stack[frame.errorSlot] = vm->error;
-            } else {
-                /* Crash. just return */
-                return n;
-            }
-        }
-    }
-
     /* Main interpreter loop */
+    mainloop:
     for (;;) {
         
         switch (*pc) {
@@ -290,10 +260,16 @@ int gst_start(Gst *vm, GstValue func) {
                 /* Call the function */
                 if (temp.type == GST_CFUNCTION) {
                     /* Save current state to vm thread */
+                    int status;
                     *((GstStackFrame *)(stack - GST_FRAME_SIZE)) = frame;
                     *vm->thread = thread;
-                    v2 = temp.data.cfunction(vm);
-                    goto ret;
+                    vm->ret.type = GST_NIL;
+                    status = temp.data.cfunction(vm);
+					v1 = vm->ret;
+					if (status == GST_RETURN_OK)
+                        goto ret;
+                    else
+                        goto vm_error;
                 } else {
                     for (; i < locals; ++i)
                         stack[i].type = GST_NIL;
@@ -308,7 +284,9 @@ int gst_start(Gst *vm, GstValue func) {
 
         case GST_OP_CST: /* Load constant value */
             gst_assert(vm, frame.callee.type == GST_FUNCTION, GST_EXPECTED_FUNCTION);
-            stack[pc[1]] = gst_vm_literal(vm, frame.callee.data.function, pc[2]);
+            if (pc[2] > frame.callee.data.function->def->literalsLen)
+                gst_error(vm, GST_NO_UPVALUE);
+            stack[pc[1]] = frame.callee.data.function->def->literals[pc[2]];
             pc += 3;
             break;
 
@@ -343,7 +321,9 @@ int gst_start(Gst *vm, GstValue func) {
                     frame.env->stackOffset = thread.count;
                     frame.env->values = NULL;
                 }
-                temp = gst_vm_literal(vm, frame.callee.data.function, pc[2]);
+                if (pc[2] > frame.callee.data.function->def->literalsLen)
+                    gst_error(vm, GST_NO_UPVALUE);
+                temp = frame.callee.data.function->def->literals[pc[2]];
                 if (temp.type != GST_NIL)
                     gst_error(vm, "cannot create closure");
                 fn = gst_alloc(vm, sizeof(GstFunction));
@@ -488,10 +468,16 @@ int gst_start(Gst *vm, GstValue func) {
                 /* Call the function */
                 if (temp.type == GST_CFUNCTION) {
                     /* Save current state to vm thread */
+                    int status;
                     *((GstStackFrame *)(stack - GST_FRAME_SIZE)) = frame;
                     *vm->thread = thread;
-                    v2 = temp.data.cfunction(vm);
-                    goto ret;
+                    vm->ret.type = GST_NIL;
+                    status = temp.data.cfunction(vm);
+                    v1 = vm->ret;
+                    if (status == GST_RETURN_OK)
+                        goto ret;
+                    else
+                        goto vm_error;
                 } else {
                     pc = temp.data.function->def->byteCode;
                 }
@@ -502,29 +488,38 @@ int gst_start(Gst *vm, GstValue func) {
             v2.type = GST_NIL;
             goto ret;
 
-        case GST_OP_GET:
-			temp = gst_get(vm, stack[pc[2]], stack[pc[3]]);
-            stack[pc[1]] = temp;
-			pc += 4;
-            break;
+        case GST_OP_GET: /* Associative get */
+        	{
+            	const char *err;
+    			err = gst_get(stack[pc[2]], stack[pc[3]], stack + pc[1]);
+    			if (err != NULL)
+					gst_error(vm, err);
+    			pc += 4;
+                break;
+        	}
 
-        case GST_OP_SET:
-			gst_set(vm, stack[pc[1]], stack[pc[2]], stack[pc[3]]);
-			pc += 4;
-            break;
+        case GST_OP_SET: /* Associative set */
+        	{
+            	const char *err;
+    			err = gst_set(vm, stack[pc[1]], stack[pc[2]], stack[pc[3]]);
+    			if (err != NULL)
+        			gst_error(vm, err);
+    			pc += 4;
+                break;
+        	}
 
-    	case GST_OP_ERR:
-			vm->error = stack[pc[1]];
-			longjmp(vm->jump, 2);
+    	case GST_OP_ERR: /* Throw error */
+			vm->ret = stack[pc[1]];
+			goto vm_error;
         	break;
 
-		case GST_OP_TRY:
+		case GST_OP_TRY: /* Begin try block */
     		frame.errorSlot = pc[1];
     		frame.errorJump = pc + *(uint32_t *)(pc + 2);
     		pc += 4;
     		break;
 
-    	case GST_OP_UTY:
+    	case GST_OP_UTY: /* End try block */
         	frame.errorJump = NULL;
 			pc++;
         	break;
@@ -560,6 +555,36 @@ int gst_start(Gst *vm, GstValue func) {
         *vm->thread = thread;
         gst_maybe_collect(vm);
     }
+
+    /* Handle errors from c functions and vm opcodes */
+    vm_error:
+        while (!frame.errorJump) {
+            /* Check for closure */
+            if (frame.env) {
+                frame.env->thread = NULL;
+                frame.env->stackOffset = frame.size;
+                frame.env->values = gst_alloc(vm, sizeof(GstValue) * frame.size);
+                gst_memcpy(frame.env->values, 
+                    thread.data + thread.count, 
+                    frame.size * sizeof(GstValue));
+            }
+            stack -= frame.prevSize + GST_FRAME_SIZE;
+            if (stack <= thread.data) {
+                thread.count = 0;
+                break;
+            }
+            frame = *((GstStackFrame *)(stack - GST_FRAME_SIZE));
+        }
+        /* If we completely unwind the stack we just return */
+        if (thread.count < GST_FRAME_SIZE)
+            return GST_RETURN_ERROR;
+        /* Jump to the error location */
+        pc = frame.errorJump;
+        /* Set error */
+        stack[frame.errorSlot] = vm->ret;
+        /* Resume vm */
+        goto mainloop;
+
 }
 
 /* Get an argument from the stack */
@@ -567,7 +592,11 @@ GstValue gst_arg(Gst *vm, uint16_t index) {
     GstValue *stack = vm->thread->data + vm->thread->count;
     GstStackFrame *frame = (GstStackFrame *)(stack - GST_FRAME_SIZE);
     uint16_t frameSize = frame->size;
-    gst_assert(vm, frameSize > index, "cannot get arg out of stack bounds");
+    if (frameSize <= index) {
+		GstValue ret;
+		ret.type = GST_NIL;
+		return ret;
+    }
     return stack[index];
 }
 
@@ -576,7 +605,7 @@ void gst_set_arg(Gst* vm, uint16_t index, GstValue x) {
     GstValue *stack = vm->thread->data + vm->thread->count;
     GstStackFrame *frame = (GstStackFrame *)(stack - GST_FRAME_SIZE);
     uint16_t frameSize = frame->size;
-    gst_assert(vm, frameSize > index, "cannot set arg out of stack bounds");
+   	if (frameSize <= index) return;
     stack[index] = x;
 }
 
@@ -590,7 +619,6 @@ uint16_t gst_count_args(Gst *vm) {
 /* Initialize the VM */
 void gst_init(Gst *vm) {
     vm->ret.type = GST_NIL;
-    vm->error.type = GST_NIL;
     vm->crash = NULL;
     /* Garbage collection */
     vm->blocks = NULL;
diff --git a/vm.h b/vm.h
index 698d40dc..ed863210 100644
--- a/vm.h
+++ b/vm.h
@@ -4,23 +4,6 @@
 #include "datatypes.h"
 #include "value.h"
 
-/* Exit from the VM normally */
-#define gst_exit(vm, r) ((vm)->ret = (r), longjmp((vm)->jump, 1))
-
-/* Bail from the VM with an error string. */
-#define gst_error(vm, e) ((vm)->error = gst_load_cstring((vm), (e)), longjmp((vm)->jump, 2))
-
-/* Crash. Not catchable, unlike error. */
-#define gst_crash(vm, e) ((vm)->crash = (e), longjmp((vm)->jump, 3))
-
-/* Error if the condition is false */
-#define gst_assert(vm, cond, e) do \
-    { if (!(cond)) { gst_error((vm), (e)); } } while (0)
-
-/* Type assertion */
-#define gst_assert_type(vm, f, t) \
-    gst_assert((vm), (f).type == (t), "Expected a different type.")
-
 /* Initialize the VM */
 void gst_init(Gst * vm);