added math library

Reviewed-on: #7

include/groundext.h

@@ -7,10 +7,30 @@
 extern "C" {
 #endif
 
+// Macro for easily returning errors
+#define ERROR(what, type) return createErrorGroundValue(createGroundError(what, type, NULL, NULL))
+
 // Forward declaration of the scope structure used in interpreter
 struct GroundScope;
 typedef struct GroundScope GroundScope;
 
+/*
+ * Stores data associated with an error thrown during Ground execution.
+ */
+typedef struct GroundError {
+    char* what;
+    char* type;
+    struct GroundInstruction* where;
+    size_t line;
+    bool hasLine;
+} GroundError;
+
+// Creates a GroundValue containing (in), with type ERROR.
+GroundValue createErrorGroundValue(GroundError in);
+
+// Creates a GroundError.
+GroundError createGroundError(char* what, char* type, GroundInstruction* where, size_t* line);
+
 /*
  * Function pointer type for native functions.
  * scope: The current execution scope (opaque).

libs/fileio/fileio.c

@@ -10,7 +10,7 @@ GroundValue native_file_read(GroundScope* scope, List args) {
     char* path = args.values[0].data.stringVal;
     FILE* f = fopen(path, "r");
     if (!f) {
-        return groundCreateValue(NONE);
+        ERROR("Failed to open file for reading", "FileError");
     }
     
     fseek(f, 0, SEEK_END);
@@ -20,7 +20,7 @@ GroundValue native_file_read(GroundScope* scope, List args) {
     char* content = malloc(fsize + 1);
     if (!content) {
         fclose(f);
-        return groundCreateValue(NONE);
+        ERROR("Failed to allocate memory for file reading", "FileError");
     }
     
     fread(content, 1, fsize, f);
@@ -42,7 +42,7 @@ GroundValue native_file_write(GroundScope* scope, List args) {
     
     FILE* f = fopen(path, "w");
     if (!f) {
-        return groundCreateValue(BOOL, 0);
+        ERROR("Failed to open file for writing", "FileError");
     }
     
     fprintf(f, "%s", content);

libs/math/math.c

@@ -0,0 +1,77 @@
+#include <groundext.h>
+#include <math.h>
+
+GroundValue ground_sin(GroundScope* scope, List args) {
+    return groundCreateValue(
+        DOUBLE,
+        sin(args.values[0].data.doubleVal)
+    );
+}
+GroundValue ground_cos(GroundScope* scope, List args) {
+    return groundCreateValue(
+        DOUBLE,
+        cos(args.values[0].data.doubleVal)
+    );
+}
+GroundValue ground_tan(GroundScope* scope, List args) {
+    return groundCreateValue(
+        DOUBLE,
+        tan(args.values[0].data.doubleVal)
+    );
+}
+
+GroundValue rad_to_deg(GroundScope* scope, List args) {
+    double radians = args.values[0].data.doubleVal;
+
+    return groundCreateValue(
+        DOUBLE,
+        radians * (180.0 / M_PI)
+    );
+}
+GroundValue deg_to_rad(GroundScope* scope, List args) {
+    double deg = args.values[0].data.doubleVal;
+
+    return groundCreateValue(
+        DOUBLE,
+        deg * (M_PI / 180.0)
+    );
+}
+
+GroundValue ground_modulos(GroundScope* scope, List args) {
+    return groundCreateValue(
+        DOUBLE,
+        fmod(args.values[0].data.doubleVal, args.values[1].data.doubleVal)
+    );
+}
+GroundValue ground_pow(GroundScope* scope, List args) {
+    return groundCreateValue(
+        DOUBLE,
+        pow(args.values[0].data.doubleVal, args.values[1].data.doubleVal)
+    );
+}
+GroundValue ground_sqrt(GroundScope* scope, List args) {
+    double value = args.values[0].data.doubleVal;
+
+    if (value < 0) {
+        ERROR("Can't get square root of number less than 0.", "InvalidMath");
+    }
+
+    return groundCreateValue(
+        DOUBLE,
+        sqrt(value)
+    );
+}
+
+void ground_init(GroundScope* scope) {
+    groundAddNativeFunction(scope, "math_Sin", ground_sin, DOUBLE, 1, DOUBLE, "radians");
+    groundAddNativeFunction(scope, "math_Cos", ground_cos, DOUBLE, 1, DOUBLE, "radians");
+    groundAddNativeFunction(scope, "math_Tan", ground_tan, DOUBLE, 1, DOUBLE, "radians");
+
+    groundAddNativeFunction(scope, "math_DegreesToRadians", deg_to_rad, DOUBLE, 1, DOUBLE, "degrees");
+    groundAddNativeFunction(scope, "math_RadiansToDegrees", rad_to_deg, DOUBLE, 1, DOUBLE, "radians");
+
+    groundAddNativeFunction(scope, "math_Modulos", ground_modulos, DOUBLE, 2, DOUBLE, "number1", DOUBLE, "number2");
+    groundAddNativeFunction(scope, "math_Pow", ground_pow, DOUBLE, 2, DOUBLE, "number1", DOUBLE, "number2");
+
+    groundAddNativeFunction(scope, "math_Sqrt", ground_sqrt, DOUBLE, 1, DOUBLE, "number");
+}

libs/request/request.c

@@ -50,21 +50,11 @@ size_t write_callback(void* ptr, size_t size, size_t nmemb, void* userdata) {
 
 // GET request
 GroundValue get_request(GroundScope* scope, List args) {
-    if (args.size < 1) {
-        printf("Requires a URL argument\n");
-        return groundCreateValue(NONE);
-    }
-    if (args.values[0].type != STRING) {
-        printf("Arg 1 needs to be a string (URL)\n");
-        return groundCreateValue(NONE);
-    }
-    
     curl_setup();
     CURL* handle = curl_easy_init();
     
     if (!handle) {
-        printf("Curl failed to init\n");
+        ERROR("CURL failed to init", "GenericRequestError");
-        return groundCreateValue(NONE);
     }
     
     ResponseBuffer buffer = {0};
@@ -81,10 +71,9 @@ GroundValue get_request(GroundScope* scope, List args) {
     CURLcode result = curl_easy_perform(handle);
     
     if (result != CURLE_OK) {
-        printf("Curl request failed: %s\n", curl_easy_strerror(result));
+        char buf[256];
-        free(buffer.data);
+        snprintf(buf, sizeof(buf) - 1, "Curl request failed: %s\n", curl_easy_strerror(result));
-        curl_easy_cleanup(handle);
+        ERROR(buf, "ActionRequestError");
-        return groundCreateValue(NONE);
     }
     
     curl_easy_cleanup(handle);
@@ -95,21 +84,11 @@ GroundValue get_request(GroundScope* scope, List args) {
 
 // POST request
 GroundValue post_request(GroundScope* scope, List args) {
-    if (args.size < 2) {
-        printf("Requires URL and POST data arguments\n");
-        return groundCreateValue(NONE);
-    }
-    if (args.values[0].type != STRING || args.values[1].type != STRING) {
-        printf("Both arguments need to be strings (URL, POST data)\n");
-        return groundCreateValue(NONE);
-    }
-    
     curl_setup();
     CURL* handle = curl_easy_init();
     
     if (!handle) {
-        printf("Curl failed to init\n");
+        ERROR("CURL failed to init", "GenericRequestError");
-        return groundCreateValue(NONE);
     }
     
     ResponseBuffer buffer = {0};
@@ -127,10 +106,11 @@ GroundValue post_request(GroundScope* scope, List args) {
     CURLcode result = curl_easy_perform(handle);
     
     if (result != CURLE_OK) {
-        printf("Curl POST request failed: %s\n", curl_easy_strerror(result));
         free(buffer.data);
+        char buf[256];
+        snprintf(buf, sizeof(buf) - 1, "Curl request failed: %s\n", curl_easy_strerror(result));
         curl_easy_cleanup(handle);
-        return groundCreateValue(NONE);
+        ERROR(buf, "ActionRequestError");
     }
     
     curl_easy_cleanup(handle);
@@ -153,27 +133,16 @@ int find_ws_slot() {
 
 // WebSocket Connect - returns connection ID as INT
 GroundValue ws_connect(GroundScope* scope, List args) {
-    if (args.size < 1) {
-        printf("Requires a WebSocket URL argument (ws:// or wss://)\n");
-        return groundCreateValue(NONE);
-    }
-    if (args.values[0].type != STRING) {
-        printf("Arg 1 needs to be a string (WebSocket URL)\n");
-        return groundCreateValue(NONE);
-    }
-    
     curl_setup();
     
     int slot = find_ws_slot();
     if (slot == -1) {
-        printf("Maximum WebSocket connections reached\n");
+        ERROR("Maximum WebSocket connections reached", "OverflowError");
-        return groundCreateValue(NONE);
     }
     
     CURL* handle = curl_easy_init();
     if (!handle) {
-        printf("Curl failed to init\n");
+        ERROR("CURL failed to init", "GenericWSError");
-        return groundCreateValue(NONE);
     }
     
     curl_easy_setopt(handle, CURLOPT_URL, args.values[0].data.stringVal);
@@ -183,9 +152,10 @@ GroundValue ws_connect(GroundScope* scope, List args) {
     CURLcode result = curl_easy_perform(handle);
     
     if (result != CURLE_OK) {
-        printf("WebSocket connection failed: %s\n", curl_easy_strerror(result));
+        char buf[256];
+        snprintf(buf, sizeof(buf) - 1, "Curl WebSocket failed: %s\n", curl_easy_strerror(result));
         curl_easy_cleanup(handle);
-        return groundCreateValue(NONE);
+        ERROR(buf, "ActionWSError");
     }
     
     ws_connections[slot].handle = handle;
@@ -197,19 +167,9 @@ GroundValue ws_connect(GroundScope* scope, List args) {
 
 // WebSocket Send - sends a text message, returns bytes sent as INT
 GroundValue ws_send(GroundScope* scope, List args) {
-    if (args.size < 2) {
-        printf("Requires connection ID and message\n");
-        return groundCreateValue(NONE);
-    }
-    if (args.values[0].type != INT || args.values[1].type != STRING) {
-        printf("Args need to be (INT connection ID, STRING message)\n");
-        return groundCreateValue(NONE);
-    }
-    
     int conn_id = (int)args.values[0].data.intVal;
     if (conn_id < 0 || conn_id >= MAX_WS_CONNECTIONS || !ws_connections[conn_id].connected) {
-        printf("Invalid or closed WebSocket connection\n");
+        ERROR("Invalid WebSocket connection ID", "GenericWSError");
-        return groundCreateValue(NONE);
     }
     
     CURL* handle = ws_connections[conn_id].handle;
@@ -219,8 +179,9 @@ GroundValue ws_send(GroundScope* scope, List args) {
     CURLcode result = curl_ws_send(handle, message, strlen(message), &sent, 0, CURLWS_TEXT);
     
     if (result != CURLE_OK) {
-        printf("WebSocket send failed: %s\n", curl_easy_strerror(result));
+        char buf[256];
-        return groundCreateValue(NONE);
+        snprintf(buf, sizeof(buf) - 1, "WebSocket send failed: %s\n", curl_easy_strerror(result));
+        ERROR(buf, "ActionWSError");
     }
     
     return groundCreateValue(INT, (int64_t)sent);
@@ -228,19 +189,9 @@ GroundValue ws_send(GroundScope* scope, List args) {
 
 // WebSocket Receive - receives a message (blocking)
 GroundValue ws_receive(GroundScope* scope, List args) {
-    if (args.size < 1) {
-        printf("Requires connection ID\n");
-        return groundCreateValue(NONE);
-    }
-    if (args.values[0].type != INT) {
-        printf("Arg 1 needs to be an INT (connection ID)\n");
-        return groundCreateValue(NONE);
-    }
-    
     int conn_id = (int)args.values[0].data.intVal;
     if (conn_id < 0 || conn_id >= MAX_WS_CONNECTIONS || !ws_connections[conn_id].connected) {
-        printf("Invalid or closed WebSocket connection\n");
+        ERROR("Invalid WebSocket connection ID", "GenericWSError");
-        return groundCreateValue(NONE);
     }
     
     CURL* handle = ws_connections[conn_id].handle;
@@ -255,8 +206,9 @@ GroundValue ws_receive(GroundScope* scope, List args) {
             // No data available right now
             return groundCreateValue(STRING, "");
         }
-        printf("WebSocket receive failed: %s\n", curl_easy_strerror(result));
+        char buf[256];
-        return groundCreateValue(NONE);
+        snprintf(buf, sizeof(buf) - 1, "WebSocket receive failed: %s\n", curl_easy_strerror(result));
+        ERROR(buf, "ActionWSError");
     }
     
     buffer[received] = '\0';
@@ -283,21 +235,11 @@ GroundValue ws_receive(GroundScope* scope, List args) {
 
 // WebSocket Receive with timeout (non-blocking version)
 GroundValue ws_receive_timeout(GroundScope* scope, List args) {
-    if (args.size < 2) {
-        printf("Requires connection ID and timeout in milliseconds\n");
-        return groundCreateValue(NONE);
-    }
-    if (args.values[0].type != INT || args.values[1].type != INT) {
-        printf("Both arguments need to be INT (connection ID, timeout_ms)\n");
-        return groundCreateValue(NONE);
-    }
-    
     int conn_id = (int)args.values[0].data.intVal;
     long timeout_ms = (long)args.values[1].data.intVal;
     
     if (conn_id < 0 || conn_id >= MAX_WS_CONNECTIONS || !ws_connections[conn_id].connected) {
-        printf("Invalid or closed WebSocket connection\n");
+        ERROR("Invalid WebSocket connection ID", "GenericWSError");
-        return groundCreateValue(NONE);
     }
     
     CURL* handle = ws_connections[conn_id].handle;
@@ -316,8 +258,9 @@ GroundValue ws_receive_timeout(GroundScope* scope, List args) {
     }
     
     if (result != CURLE_OK) {
-        printf("WebSocket receive failed: %s\n", curl_easy_strerror(result));
+        char buf[256];
-        return groundCreateValue(NONE);
+        snprintf(buf, sizeof(buf) - 1, "WebSocket receive failed: %s\n", curl_easy_strerror(result));
+        ERROR(buf, "ActionWSError");
     }
     
     buffer[received] = '\0';
@@ -341,19 +284,9 @@ GroundValue ws_receive_timeout(GroundScope* scope, List args) {
 
 // WebSocket Close - properly close a connection, returns BOOL success
 GroundValue ws_close(GroundScope* scope, List args) {
-    if (args.size < 1) {
-        printf("Requires connection ID\n");
-        return groundCreateValue(NONE);
-    }
-    if (args.values[0].type != INT) {
-        printf("Arg 1 needs to be an INT (connection ID)\n");
-        return groundCreateValue(NONE);
-    }
-    
     int conn_id = (int)args.values[0].data.intVal;
     if (conn_id < 0 || conn_id >= MAX_WS_CONNECTIONS || !ws_connections[conn_id].connected) {
-        printf("Invalid or already closed WebSocket connection\n");
+        ERROR("Invalid or already connected websocket", "GenericWSError");
-        return groundCreateValue(BOOL, false);
     }
     
     CURL* handle = ws_connections[conn_id].handle;
@@ -374,19 +307,9 @@ GroundValue ws_close(GroundScope* scope, List args) {
 
 // WebSocket Send Binary data, returns bytes sent as INT
 GroundValue ws_send_binary(GroundScope* scope, List args) {
-    if (args.size < 2) {
-        printf("Requires connection ID and binary data\n");
-        return groundCreateValue(NONE);
-    }
-    if (args.values[0].type != INT || args.values[1].type != STRING) {
-        printf("Args need to be (INT connection ID, STRING binary data)\n");
-        return groundCreateValue(NONE);
-    }
-    
     int conn_id = (int)args.values[0].data.intVal;
     if (conn_id < 0 || conn_id >= MAX_WS_CONNECTIONS || !ws_connections[conn_id].connected) {
-        printf("Invalid or closed WebSocket connection\n");
+        ERROR("Invalid WebSocket connection ID", "GenericWSError");
-        return groundCreateValue(NONE);
     }
     
     CURL* handle = ws_connections[conn_id].handle;
@@ -396,8 +319,9 @@ GroundValue ws_send_binary(GroundScope* scope, List args) {
     CURLcode result = curl_ws_send(handle, data, strlen(data), &sent, 0, CURLWS_BINARY);
     
     if (result != CURLE_OK) {
-        printf("WebSocket binary send failed: %s\n", curl_easy_strerror(result));
+        char buf[256];
-        return groundCreateValue(NONE);
+        snprintf(buf, sizeof(buf) - 1, "WebSocket binary send failed: %s\n", curl_easy_strerror(result));
+        ERROR(buf, "ActionWSError");
     }
     
     return groundCreateValue(INT, (int64_t)sent);

src/interpreter.c

@@ -11,7 +11,9 @@
 
 int currentInstruction = 0;
 
-void runtimeError(GroundRuntimeError error, char* what, GroundInstruction* where, int whereLine) {
+bool isMainScopeGlobal = true;
+
+[[noreturn]] void runtimeError(GroundRuntimeError error, char* what, GroundInstruction* where, int whereLine) {
     printf("Ground runtime error:\n  ErrorType: ");
     switch (error) {
         case ARG_TYPE_MISMATCH: {
@@ -46,6 +48,18 @@ void runtimeError(GroundRuntimeError error, char* what, GroundInstruction* where
             printf("MathError");
             break;
         }
+        case RETURN_TYPE_MISMATCH: {
+            printf("ReturnTypeMismatch");
+            break;
+        }
+        case PREMATURE_EOF: {
+            printf("PrematureEof");
+            break;
+        }
+        case INVALID_INSTRUCTION: {
+            printf("InvalidInstruction");
+            break;
+        }
         default:
         case FIXME: {
             printf("FIXME (please report issue to https://chsp.au/ground/cground)");
@@ -66,6 +80,22 @@ void runtimeError(GroundRuntimeError error, char* what, GroundInstruction* where
     exit(1);
 }
 
+[[noreturn]] void throwError(GroundError* error) {
+    printf("Uncaught Ground runtime error:\n  ErrorType: %s\n", error->type);
+    if (error->what != NULL) {
+        printf("  ErrorContext: %s\n", error->what);
+    }
+    if (error->where != NULL) {
+        printf("  ErrorInstruction: ");
+        printGroundInstruction(error->where);
+        printf("\n");
+    }
+    if (error->hasLine) {
+        printf("  ErrorLine: %zu\n", error->line + 1);
+    }
+    exit(1);
+}
+
 GroundLabel* findLabel(GroundLabel* head, const char *id) {
     GroundLabel *item;
     HASH_FIND_STR(head, id, item);
@@ -173,7 +203,7 @@ GroundDebugInstruction parseDebugInstruction(char* in) {
         }
     }
 
-    if (spacepos == -1) {
+    if (spacepos == (size_t) -1) {
         spacepos = insize;
     }
 
@@ -234,6 +264,186 @@ void groundAddNativeFunction(GroundScope* scope, char* name, NativeGroundFunctio
     addVariable(scope->variables, name, createFunctionGroundValue(gf));
 }
 
+GroundFunction* parseFunction(GroundProgram* in, size_t errorOffset) {
+    GroundFunction* function = createGroundFunction();
+    for (size_t i = 0; i < in->size; i++) {
+        if (in->instructions[i].args.length < 2) {
+            function->returnType = NONE;
+        } else {
+            if (in->instructions[i].args.args[1].type != TYPEREF) {
+                runtimeError(ARG_TYPE_MISMATCH, "Expecting a TypeRef for arg 2", &in->instructions[i], errorOffset + i);
+            }
+            GroundArg* args = in->instructions[i].args.args;
+            function->returnType = stringToValueType(args[1].value.refName);
+            size_t length = in->instructions[i].args.length;
+            for (size_t j = 2; j < length; j += 2) {
+                if (args[j].type != TYPEREF) {
+                    runtimeError(ARG_TYPE_MISMATCH, "Expecting a TypeRef", &in->instructions[i], errorOffset + i);
+                }
+                if (j + 1 >= length) {
+                    runtimeError(TOO_FEW_ARGS, "Expecting a DirectRef after a TypeRef", &in->instructions[i], errorOffset + i);
+                }
+                if (args[j + 1].type != DIRREF) {
+                    runtimeError(ARG_TYPE_MISMATCH, "Expecting a DirectRef after a TypeRef", &in->instructions[i], errorOffset + i);
+                }
+                addArgsToGroundFunction(function, stringToValueType(args[j].value.refName), args[j + 1].value.refName);
+            }
+        }
+        i++;
+        while (i < in->size) {
+            addInstructionToProgram(&function->program, in->instructions[i]);
+            i++;
+        }
+        break;
+    }
+    return function;
+}
+
+GroundStruct parseStruct(GroundProgram* in, GroundScope* scope, size_t errorOffset) {
+    GroundStruct gstruct = createStruct();
+    for (size_t i = 0; i < in->size; i++) {
+        switch (in->instructions[i].type) {
+            case SET: {
+                if (in->instructions[i].args.length < 2) {
+                    runtimeError(TOO_FEW_ARGS, "Expecting 2 args", &in->instructions[i], i + errorOffset);
+                }
+                if (in->instructions[i].args.length > 2) {
+                    runtimeError(TOO_MANY_ARGS, "Expecting 2 args", &in->instructions[i], i + errorOffset);
+                }
+                if (in->instructions[i].args.args[0].type != DIRREF) {
+                    runtimeError(ARG_TYPE_MISMATCH, "Expecting a DirectRef for arg 1", &in->instructions[i], i + errorOffset);
+                }
+                if (in->instructions[i].args.args[1].type != VALUE) {
+                    runtimeError(ARG_TYPE_MISMATCH, "Expecting a Value for arg 2", &in->instructions[i], i + errorOffset);
+                }
+                addFieldToStruct(&gstruct, in->instructions[i].args.args[0].value.refName, in->instructions[i].args.args[1].value.value);
+                break;
+            }
+            case INIT: {
+                if (in->instructions[i].args.length < 2) {
+                    runtimeError(TOO_FEW_ARGS, "Expecting 2 args", &in->instructions[i], currentInstruction);
+                }
+                if (in->instructions[i].args.length > 2) {
+                    runtimeError(TOO_MANY_ARGS, "Expecting 2 args", &in->instructions[i], currentInstruction);
+                }
+                if (in->instructions[i].args.args[0].type != DIRREF) {
+                    runtimeError(ARG_TYPE_MISMATCH, "Expecting a DirectRef for arg 1", &in->instructions[i], currentInstruction);
+                }
+                if (in->instructions[i].args.args[1].type != TYPEREF) {
+                    runtimeError(ARG_TYPE_MISMATCH, "Expecting a TypeRef for arg 2", &in->instructions[i], currentInstruction);
+                }
+
+                GroundValue gv;
+
+                switch (stringToValueType(in->instructions[i].args.args[0].value.refName)) {
+                    case INT: {
+                        gv = createIntGroundValue(0);
+                        break;
+                    }
+                    case DOUBLE: {
+                        gv = createDoubleGroundValue(0);
+                        break;
+                    }
+                    case STRING: {
+                        gv = createStringGroundValue("");
+                        break;
+                    }
+                    case CHAR: {
+                        gv = createCharGroundValue('\0');
+                        break;
+                    }
+                    case BOOL: {
+                        gv = createBoolGroundValue(false);
+                        break;
+                    }
+                    case LIST: {
+                        gv = createListGroundValue(createList());
+                        break;
+                    }
+                    case FUNCTION: {
+                        gv = createFunctionGroundValue(createGroundFunction());
+                        break;
+                    }
+                    case STRUCTVAL: {
+                        gv.type = STRUCTVAL;
+                        gv.data.structVal = malloc(sizeof(GroundStruct));
+                        *gv.data.structVal = createStruct();
+                        break;
+                    }
+                    case CUSTOM: {
+                        GroundVariable* var = findVariable(*scope->variables, in->instructions[i].args.args[1].value.refName);
+                        if (var == NULL) {
+                            runtimeError(UNKNOWN_VARIABLE, "Couldn't find the specified type", &in->instructions[i], currentInstruction);
+                        }
+                        if (var->value.type != STRUCTVAL) {
+                            runtimeError(ARG_TYPE_MISMATCH, "TypeRef does not reference a struct", &in->instructions[i], currentInstruction);
+                        }
+                        GroundStruct* gstruct = var->value.data.structVal;
+                        gv.type = CUSTOM;
+                        gv.data.customVal = malloc(sizeof(GroundObject));
+                        *gv.data.customVal = createObject(*gstruct);
+                        break;
+                    }
+                    case NONE: {
+                        gv.type = NONE;
+                        break;
+                    }
+                    default: {
+                        runtimeError(FIXME, "Reached should-be-impossible state", &in->instructions[i], currentInstruction);
+                        break;
+                    }
+                }
+                addFieldToStruct(&gstruct, in->instructions[i].args.args[0].value.refName, gv);
+
+                break;
+            }
+            case FUN: {
+                if (in->instructions[i].args.length < 1) {
+                    runtimeError(TOO_FEW_ARGS, "Expecting 1 or more args", &in->instructions[i], i);
+                }
+                if (in->instructions[i].args.args[0].type != FNREF) {
+                    runtimeError(ARG_TYPE_MISMATCH, "Expecting a FunctionRef for arg 1", &in->instructions[i], i);
+                }
+                char* name = malloc(strlen(in->instructions[i].args.args[0].value.refName) + 1);
+                strcpy(name, in->instructions[i].args.args[0].value.refName);
+
+                size_t counter = 1;
+                GroundProgram gp = createGroundProgram();
+                addInstructionToProgram(&gp, in->instructions[i]);
+                size_t errorOffset = i;
+                i++;
+                while (counter > 0) {
+                    if (i >= in->size) {
+                        runtimeError(PREMATURE_EOF, "Reached end of scope before function definition ended", &in->instructions[i - 1], i - 1);
+                    }
+                    if (in->instructions[i].type == FUN) {
+                        counter++;
+                    }
+                    if (in->instructions[i].type == ENDFUN) {
+                        counter--;
+                    }
+                    addInstructionToProgram(&gp, in->instructions[i]);
+                    i++;
+                }
+
+                GroundFunction* function = parseFunction(&gp, errorOffset);
+                function->startLine = i;
+                GroundValue gv = createFunctionGroundValue(function);
+                addFieldToStruct(&gstruct, name, gv);
+                break;
+            }
+            case ENDSTRUCT: {
+                break;
+            }
+            default: {
+                runtimeError(INVALID_INSTRUCTION, "Unsupported instruction while inside struct", &in->instructions[i], errorOffset + i);
+            }
+
+        }
+    }
+    return gstruct;
+}
+
 GroundValue interpretGroundProgram(GroundProgram* in, GroundScope* inScope) {
     GroundLabel* labels = NULL;
     GroundVariable* variables = NULL;
@@ -246,52 +456,89 @@ GroundValue interpretGroundProgram(GroundProgram* in, GroundScope* inScope) {
         scope.labels = &labels;
         scope.variables = &variables;
     }
-    // Preprocess all labels and functions
+    scope.isMainScope = isMainScopeGlobal;
-    for (int i = 0; i < in->size; i++) {
+    isMainScopeGlobal = false;
+    // Preprocess all labels, structs and functions
+    for (size_t i = 0; i < in->size; i++) {
         if (in->instructions[i].type == CREATELABEL) {
             addLabel(scope.labels, in->instructions[i].args.args[0].value.refName, i);
         }
         if (in->instructions[i].type == FUN) {
-            GroundFunction* function = createGroundFunction();
-            function->startLine = i;
             if (in->instructions[i].args.length < 1) {
                 runtimeError(TOO_FEW_ARGS, "Expecting 1 or more args", &in->instructions[i], i);
             }
             if (in->instructions[i].args.args[0].type != FNREF) {
                 runtimeError(ARG_TYPE_MISMATCH, "Expecting a FunctionRef for arg 1", &in->instructions[i], i);
             }
-            char* functionName = in->instructions[i].args.args[0].value.refName;
+            char* name = malloc(strlen(in->instructions[i].args.args[0].value.refName) + 1);
-            if (in->instructions[i].args.length < 2) {
+            strcpy(name, in->instructions[i].args.args[0].value.refName);
-                function->returnType = NONE;
+
-            } else {
+            size_t counter = 1;
-                if (in->instructions[i].args.args[1].type != TYPEREF) {
+            GroundProgram gp = createGroundProgram();
-                    runtimeError(ARG_TYPE_MISMATCH, "Expecting a TypeRef for arg 2", &in->instructions[i], i);
+            addInstructionToProgram(&gp, in->instructions[i]);
-                }
+            size_t errorOffset = i;
-                GroundArg* args = in->instructions[i].args.args;
-                function->returnType = stringToValueType(args[1].value.refName);
-                size_t length = in->instructions[i].args.length;
-                for (size_t j = 2; j < length; j += 2) {
-                    if (args[j].type != TYPEREF) {
-                        runtimeError(ARG_TYPE_MISMATCH, "Expecting a TypeRef", &in->instructions[i], i);
-                    }
-                    if (j + 1 >= length) {
-                        runtimeError(TOO_FEW_ARGS, "Expecting a DirectRef after a TypeRef", &in->instructions[i], i);
-                    }
-                    if (args[j + 1].type != DIRREF) {
-                        runtimeError(ARG_TYPE_MISMATCH, "Expecting a DirectRef after a TypeRef", &in->instructions[i], i);
-                    }
-                    addArgsToGroundFunction(function, stringToValueType(args[j].value.refName), args[j + 1].value.refName);
-                }
-            }
             i++;
-            while (in->instructions[i].type != ENDFUN) {
+            while (counter > 0) {
-                addInstructionToProgram(&function->program, in->instructions[i]);
+                if (i >= in->size) {
+                    runtimeError(PREMATURE_EOF, "Reached end of scope before function definition ended", &in->instructions[i - 1], i - 1);
+                }
+                if (in->instructions[i].type == FUN) {
+                    counter++;
+                }
+                if (in->instructions[i].type == ENDFUN) {
+                    counter--;
+                }
+                addInstructionToProgram(&gp, in->instructions[i]);
                 i++;
             }
-            addVariable(scope.variables, functionName, createFunctionGroundValue(function));
+
+            GroundFunction* function = parseFunction(&gp, errorOffset);
+            function->startLine = i;
+            GroundValue gv = createFunctionGroundValue(function);
+
+            addVariable(scope.variables, name, gv);
+        }
+        if (in->instructions[i].type == STRUCT) {
+            if (in->instructions[i].args.length < 1) {
+                runtimeError(TOO_FEW_ARGS, "Expecting 1 arg", &in->instructions[i], i);
+            }
+            if (in->instructions[i].args.length > 1) {
+                runtimeError(TOO_MANY_ARGS, "Expecting 1 arg", &in->instructions[i], i);
+            }
+            if (in->instructions[i].args.args[0].type != TYPEREF) {
+                runtimeError(ARG_TYPE_MISMATCH, "Expected arg 1 to be a typeref", &in->instructions[i], i);
+            }
+            char* name = malloc(strlen(in->instructions[i].args.args[0].value.refName) + 1);
+            strcpy(name, in->instructions[i].args.args[0].value.refName);
+            i++;
+
+            size_t counter = 1;
+            GroundProgram gp = createGroundProgram();
+            size_t errorOffset = i;
+            while (counter > 0) {
+                if (i >= in->size) {
+                    runtimeError(PREMATURE_EOF, "Reached end of scope before struct definition ended", &in->instructions[i - 1], i - 1);
+                }
+                if (in->instructions[i].type == STRUCT) {
+                    counter++;
+                }
+                if (in->instructions[i].type == ENDSTRUCT) {
+                    counter--;
+                }
+                addInstructionToProgram(&gp, in->instructions[i]);
+                i++;
+            }
+
+            GroundValue gv = {
+                .type = STRUCTVAL,
+                .data.structVal = malloc(sizeof(GroundStruct))
+            };
+            *gv.data.structVal = parseStruct(&gp, &scope, errorOffset);
+
+            addVariable(scope.variables, name, gv);
         }
     }
-    for (int i = 0; i < in->size; i++) {
+    for (size_t i = 0; i < in->size; i++) {
         if (in->instructions[i].type == FUN) {
             int count = 1;
             while (count > 0) {
@@ -307,6 +554,21 @@ GroundValue interpretGroundProgram(GroundProgram* in, GroundScope* inScope) {
                 }
             }
         }
+        if (in->instructions[i].type == STRUCT) {
+            int count = 1;
+            while (count > 0) {
+                i++;
+                if (i >= in->size) {
+                    return createNoneGroundValue();
+                }
+                if (in->instructions[i].type == STRUCT) {
+                    count++;
+                }
+                if (in->instructions[i].type == ENDSTRUCT) {
+                    count--;
+                }
+            }
+        }
         if (in->instructions[i].type == PAUSE || instructionsToPause == 0) {
             printf("Paused execution\n");
             printf("Previous instruction: ");
@@ -428,7 +690,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
     GroundInstruction* in = &copied_inst;
 
     // Insert variables prefixed with $
-    for (int i = 0; i < in->args.length; i++) {
+    for (size_t i = 0; i < in->args.length; i++) {
         if (in->args.args[i].type == VALREF) {
             GroundVariable* variable = findVariable(*scope->variables, in->args.args[i].value.refName);
             if (variable) {
@@ -441,9 +703,11 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
         }
     }
     switch (in->type) {
-        // We can safely ignore any CREATELABEL, FUN, and ENDFUN instructions, these have been preprocessed
+        // We can safely ignore these instructions, as they have been preprocessed
         case FUN:
         case ENDFUN:
+        case STRUCT:
+        case ENDSTRUCT:
         case CREATELABEL: {
             break;
         }
@@ -516,7 +780,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
             if (in->args.length < 1) {
                 runtimeError(TOO_FEW_ARGS, "Expecting 1 or more args", in, currentInstruction);
             }
-            for (int i = 0; i < in->args.length; i++) {
+            for (size_t i = 0; i < in->args.length; i++) {
                 if (i != 0) printf(" ");
                 printGroundArg(&in->args.args[i]);
             }
@@ -526,7 +790,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
             if (in->args.length < 1) {
                 runtimeError(TOO_FEW_ARGS, "Expecting 1 or more args", in, currentInstruction);
             }
-            for (int i = 0; i < in->args.length; i++) {
+            for (size_t i = 0; i < in->args.length; i++) {
                 if (i != 0) printf(" ");
                 printGroundArg(&in->args.args[i]);
             }
@@ -618,9 +882,19 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                 }
                 case FUNCTION: {
                     addVariable(scope->variables, in->args.args[1].value.refName, createStringGroundValue("function"));
+                    break;
+                }
+                case STRUCTVAL: {
+                    addVariable(scope->variables, in->args.args[1].value.refName, createStringGroundValue("struct"));
+                    break;
                 }
                 case NONE: {
                     addVariable(scope->variables, in->args.args[1].value.refName, createStringGroundValue("none"));
+                    break;
+                }
+                case ERROR: {
+                    addVariable(scope->variables, in->args.args[1].value.refName, createStringGroundValue("error"));
+                    break;
                 }
             }
 
@@ -655,7 +929,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                 runtimeError(ARG_TYPE_MISMATCH, "Expecting a DirectRef for arg 1", in, currentInstruction);
             }
             List newList = createList();
-            for (int i = 1; i < in->args.length; i++) {
+            for (size_t i = 1; i < in->args.length; i++) {
                 if (in->args.args[i].type != VALUE) {
                     runtimeError(ARG_TYPE_MISMATCH, "Expecting a Value for all args after arg 1", in, currentInstruction);
                 }
@@ -1132,7 +1406,7 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                 runtimeError(ARG_TYPE_MISMATCH, "Expecting a DirectRef for arg 3", in, currentInstruction);
             }
             char* str = in->args.args[0].value.value.data.stringVal;
-            int64_t idx = in->args.args[1].value.value.data.intVal;
+            size_t idx = in->args.args[1].value.value.data.intVal;
             if (idx < strlen(str)) {
                 addVariable(scope->variables, in->args.args[2].value.refName, createCharGroundValue(str[idx]));
             } else {
@@ -1487,6 +1761,15 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                 
                 if (function->nativeFn) {
                     GroundValue returnValue = function->nativeFn(scope, argsList);
+                    if (returnValue.type == ERROR) {
+                        returnValue.data.errorVal.line = currentInstruction;
+                        returnValue.data.errorVal.hasLine = true;
+                        returnValue.data.errorVal.where = in;
+                        if (scope->isMainScope) {
+                            throwError(&returnValue.data.errorVal);
+                        }
+                        return returnValue;
+                    }
                     if (returnValue.type != function->returnType) {
                          runtimeError(RETURN_TYPE_MISMATCH, "Unexpected return value type from native function", in, currentInstruction);
                     }
@@ -1506,6 +1789,9 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
                 size_t currentCurrentInstruction = currentInstruction;
                 currentInstruction = function->startLine;
                 GroundValue returnValue = interpretGroundProgram(&function->program, &newScope);
+                if (returnValue.type == ERROR) {
+                    return returnValue;
+                }
                 if (returnValue.type != function->returnType) {
                     runtimeError(RETURN_TYPE_MISMATCH, "Unexpected return value type from function", in, currentInstruction);
                 }
@@ -1628,6 +1914,87 @@ GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scop
             break;
         }
 
+        case INIT: {
+            if (in->args.length < 2) {
+                runtimeError(TOO_FEW_ARGS, "Expecting 2 args", in, currentInstruction);
+            }
+            if (in->args.length > 2) {
+                runtimeError(TOO_MANY_ARGS, "Expecting 2 args", in, currentInstruction);
+            }
+            if (in->args.args[0].type != DIRREF) {
+                runtimeError(ARG_TYPE_MISMATCH, "Expecting a DirectRef for arg 1", in, currentInstruction);
+            }
+            if (in->args.args[1].type != TYPEREF) {
+                runtimeError(ARG_TYPE_MISMATCH, "Expecting a TypeRef for arg 2", in, currentInstruction);
+            }
+
+            GroundValue gv;
+
+            switch (stringToValueType(in->args.args[1].value.refName)) {
+                case INT: {
+                    gv = createIntGroundValue(0);
+                    break;
+                }
+                case DOUBLE: {
+                    gv = createDoubleGroundValue(0);
+                    break;
+                }
+                case STRING: {
+                    gv = createStringGroundValue("");
+                    break;
+                }
+                case CHAR: {
+                    gv = createCharGroundValue('\0');
+                    break;
+                }
+                case BOOL: {
+                    gv = createBoolGroundValue(false);
+                    break;
+                }
+                case LIST: {
+                    gv = createListGroundValue(createList());
+                    break;
+                }
+                case FUNCTION: {
+                    GroundFunction* gf = createGroundFunction();
+                    gf->returnType = NONE;
+                    gv = createFunctionGroundValue(gf);
+                    break;
+                }
+                case STRUCTVAL: {
+                    gv.type = STRUCTVAL;
+                    gv.data.structVal = malloc(sizeof(GroundStruct));
+                    *gv.data.structVal = createStruct();
+                    break;
+                }
+                case CUSTOM: {
+                    GroundVariable* var = findVariable(*scope->variables, in->args.args[1].value.refName);
+                    if (var == NULL) {
+                        runtimeError(UNKNOWN_VARIABLE, "Couldn't find the specified type", in, currentInstruction);
+                    }
+                    if (var->value.type != STRUCTVAL) {
+                        runtimeError(ARG_TYPE_MISMATCH, "TypeRef does not reference a struct", in, currentInstruction);
+                    }
+                    GroundStruct* gstruct = var->value.data.structVal;
+                    gv.type = CUSTOM;
+                    gv.data.customVal = malloc(sizeof(GroundObject));
+                    *gv.data.customVal = createObject(*gstruct);
+                    break;
+                }
+                case NONE: {
+                    gv.type = NONE;
+                    break;
+                }
+                default: {
+                    runtimeError(FIXME, "Reached should-be-impossible state", in, currentInstruction);
+                    break;
+                }
+            }
+            addVariable(scope->variables, in->args.args[0].value.refName, gv);
+
+            break;
+        }
+
         case DROP: {
             if (in->args.length < 1) {
                 runtimeError(TOO_FEW_ARGS, "Expecting 1 arg", in, currentInstruction);

src/interpreter.h

@@ -7,7 +7,7 @@
 #include "include/uthash.h"
 
 typedef enum GroundRuntimeError {
-    ARG_TYPE_MISMATCH, TOO_FEW_ARGS, TOO_MANY_ARGS, UNKNOWN_LABEL, UNKNOWN_VARIABLE, LIST_ERROR, STRING_ERROR, MATH_ERROR, RETURN_TYPE_MISMATCH, FIXME
+    ARG_TYPE_MISMATCH, TOO_FEW_ARGS, TOO_MANY_ARGS, UNKNOWN_LABEL, UNKNOWN_VARIABLE, LIST_ERROR, STRING_ERROR, MATH_ERROR, RETURN_TYPE_MISMATCH, PREMATURE_EOF, INVALID_INSTRUCTION, FIXME
 } GroundRuntimeError;
 
 typedef enum GroundDebugInstructionType {
@@ -29,6 +29,7 @@ typedef struct GroundVariable {
 typedef struct GroundScope {
     GroundLabel** labels;
     GroundVariable** variables;
+    bool isMainScope;
 } GroundScope;
 
 typedef struct GroundDebugInstruction {
@@ -36,8 +37,12 @@ typedef struct GroundDebugInstruction {
     char* arg;
 } GroundDebugInstruction;
 
+GroundStruct parseStruct(GroundProgram* in, GroundScope* scope, size_t errorOffset); 
+GroundFunction* parseFunction(GroundProgram* in, size_t errorOffset);
 GroundValue interpretGroundProgram(GroundProgram* in, GroundScope* inScope);
 GroundValue interpretGroundInstruction(GroundInstruction inst, GroundScope* scope);
 
 
+
+
 #endif

src/types.c

@@ -51,6 +51,13 @@ GroundValue createFunctionGroundValue(GroundFunction* in) {
     return gv;
 }
 
+GroundValue createErrorGroundValue(GroundError in) {
+    GroundValue gv;
+    gv.data.errorVal = in;
+    gv.type = ERROR;
+    return gv;
+}
+
 GroundValue createNoneGroundValue() {
     GroundValue gv;
     gv.type = NONE;
@@ -74,7 +81,7 @@ GroundValue copyGroundValue(const GroundValue* gv) {
             break;
         case LIST: {
             List newList = createList();
-            for (int i = 0; i < gv->data.listVal.size; i++) {
+            for (size_t i = 0; i < gv->data.listVal.size; i++) {
                 // Recursive call to handle nested lists and other types
                 appendToList(&newList, copyGroundValue(&gv->data.listVal.values[i]));
             }
@@ -93,6 +100,10 @@ GroundValue copyGroundValue(const GroundValue* gv) {
             // FIXME
             newGv.data.customVal = gv->data.customVal;
             break;
+        case NONE:
+        default: {
+
+        }
     }
     return newGv;
 }
@@ -125,7 +136,7 @@ void printGroundValue(GroundValue* gv) {
         }
         case LIST: {
             printf("[");
-            for (int i = 0; i < gv->data.listVal.size; i++) {
+            for (size_t i = 0; i < gv->data.listVal.size; i++) {
                 printGroundValue(&gv->data.listVal.values[i]);
                 if (i < gv->data.listVal.size - 1) {
                     printf(", ");
@@ -152,7 +163,7 @@ void freeGroundValue(GroundValue* gv) {
     }
     if (gv->type == LIST && gv->data.listVal.values != NULL) {
         List* list = &gv->data.listVal;
-        for (int i = 0; i < list->size; i++) {
+        for (size_t i = 0; i < list->size; i++) {
             freeGroundValue(&list->values[i]);
         }
         free(list->values);
@@ -164,6 +175,18 @@ void freeGroundValue(GroundValue* gv) {
         freeGroundStruct(gstruct);
         free(gstruct);
     }
+    if (gv->type == ERROR) {
+        GroundError* error = &gv->data.errorVal;
+        if (error->type != NULL) {
+            free(error->type);
+        }
+        if (error->what != NULL) {
+            free(error->what);
+        }
+        if (error->where != NULL) {
+            freeGroundInstruction(error->where);
+        }
+    } 
 }
 
 GroundArg createValueGroundArg(GroundValue value) {
@@ -394,7 +417,7 @@ void printGroundInstruction(GroundInstruction* gi) {
             break;
     }
     if (gi->type != CREATELABEL) printf(" ");
-    for (int i = 0; i < gi->args.length; i++) {
+    for (size_t i = 0; i < gi->args.length; i++) {
         if (gi->args.args[i].type == VALUE && gi->args.args[i].value.value.type == STRING) {
             printf("\"");
             printGroundArg(&gi->args.args[i]);
@@ -428,7 +451,7 @@ void appendToList(List* list, GroundValue value) {
     list->values[list->size - 1] = value;
 }
 
-ListAccess getListAt(List* list, int idx) {
+ListAccess getListAt(List* list, size_t idx) {
     if (list == NULL) {
         printf("Expecting a List ptr, got a null pointer instead.\nThis is likely not an error with your Ground program.\nPlease report this issue to https://chsp.au/ground/cground\n");
         exit(EXIT_FAILURE);
@@ -446,7 +469,7 @@ ListAccess getListAt(List* list, int idx) {
     }
 }
 
-ListAccessStatus setListAt(List* list, int idx, GroundValue value) {
+ListAccessStatus setListAt(List* list, size_t idx, GroundValue value) {
     if (list == NULL) {
         printf("Expecting a List ptr, got a null pointer instead.\nThis is likely not an error with your Ground program.\nPlease report this issue to https://chsp.au/ground/cground\n");
         exit(EXIT_FAILURE);
@@ -525,3 +548,37 @@ void freeGroundObject(GroundObject* object) {
     }
     object->fields = NULL;
 }
+
+GroundError createGroundError(char* what, char* type, GroundInstruction* where, size_t* line) {
+    GroundError ge;
+    if (what != NULL) {
+        ge.what = malloc(strlen(what) + 1);
+        strcpy(ge.what, what);
+    } else {
+        ge.what = NULL;
+    }
+
+    if (type != NULL) {
+        ge.type = malloc(strlen(type) + 1);
+        strcpy(ge.type, type);
+    } else {
+        ge.type = malloc(strlen("GenericError") + 1);
+        strcpy(ge.type, "GenericError");
+    }
+
+    if (where != NULL) {
+        ge.where = malloc(sizeof(GroundInstruction));
+        *ge.where = copyGroundInstruction(where);
+    } else {
+        ge.where = NULL;
+    }
+
+    if (line != NULL) {
+        ge.line = *line;
+    } else {
+        ge.line = 0;
+        ge.hasLine = false;
+    }
+
+    return ge;
+}

src/types.h

@@ -13,7 +13,7 @@ typedef enum GroundInstType {
 } GroundInstType;
 
 typedef enum GroundValueType {
-    INT, DOUBLE, STRING, CHAR, BOOL, LIST, FUNCTION, STRUCTVAL, CUSTOM, NONE
+    INT, DOUBLE, STRING, CHAR, BOOL, LIST, FUNCTION, STRUCTVAL, CUSTOM, ERROR, NONE
 } GroundValueType;
 
 typedef enum GroundArgType {
@@ -29,6 +29,7 @@ struct GroundFunction;
 struct GroundScope;
 struct GroundStruct;
 struct GroundObject;
+struct GroundInstruction;
 
 struct List;
 
@@ -42,6 +43,17 @@ typedef struct List {
     struct GroundValue* values;
 } List;
 
+/*
+ * Stores data associated with an error thrown during Ground execution.
+ */
+typedef struct GroundError {
+    char* what;
+    char* type;
+    struct GroundInstruction* where;
+    size_t line;
+    bool hasLine;
+} GroundError;
+
 /*
  * Stores literal values created in a Ground program.
  * Associated functions:
@@ -57,6 +69,7 @@ typedef struct GroundValue {
         char charVal;
         bool boolVal;
         List listVal;
+        GroundError errorVal;
         struct GroundFunction* fnVal;
         struct GroundStruct* structVal;
         struct GroundObject* customVal;
@@ -187,6 +200,9 @@ GroundValue createListGroundValue(List in);
 // Creates a GroundValue conatining (in), with type FUNCTION.
 GroundValue createFunctionGroundValue(GroundFunction* in);
 
+// Creates a GroundValue containing (in), with type ERROR.
+GroundValue createErrorGroundValue(GroundError in);
+
 // Creates a Groundvalue with type NONE.
 GroundValue createNoneGroundValue();
 
@@ -234,10 +250,10 @@ void appendToList(List* list, GroundValue value);
 
 // Gets item at index (idx) from list (list). If there is an error, it
 // will be indicated in the status field.
-ListAccess getListAt(List* list, int idx);
+ListAccess getListAt(List* list, size_t idx);
 
 // Sets an item in list (list) at index (idx) to GroundValue (value).
-ListAccessStatus setListAt(List* list, int idx, GroundValue value);
+ListAccessStatus setListAt(List* list, size_t idx, GroundValue value);
 
 // Creates a Ground struct
 GroundStruct createStruct();
@@ -257,4 +273,9 @@ GroundObjectField* findField(GroundObject head, const char *id);
 // Frees a GroundObject
 void freeGroundObject(GroundObject* object);
 
+// Creates a GroundError.
+GroundError createGroundError(char* what, char* type, GroundInstruction* where, size_t* line);
+
+
+
 #endif