feat: add return statements and modify OP_RETURN opcode behaviour at runtime

Author: aymaneelmaini

src/compiler.c

@@ -184,6 +184,7 @@ static int emit_jump(u8 instruction)
 
 static void emit_return()
 {
+    emit_byte(OP_NIL);
     emit_byte(OP_RETURN);
 }
 
@@ -796,6 +797,25 @@ static void print_statement()
     emit_byte(OP_PRINT);
 }
 
+static void return_statement()
+{
+    if (current->type == TYPE_SCRIPT)
+    {
+        error("Can't return from top-level code");
+    }
+
+    if (match(TOKEN_SEMICOLON))
+    {
+        emit_return();
+    }
+    else
+    {
+        expression();
+        consume(TOKEN_SEMICOLON, "Expect semicolon after return value;");
+        emit_byte(OP_RETURN);
+    }
+}
+
 static void while_statement()
 {
     int loop_start = current_chunk()->count;
@@ -865,6 +885,8 @@ static void statement()
         for_statement();
     else if (match(TOKEN_IF))
         if_statement();
+    else if (match(TOKEN_RETURN))
+        return_statement();
     else if (match(TOKEN_WHILE))
         while_statement();
     else if (match(TOKEN_LEFT_BRACE))

src/vm.c

@@ -323,7 +323,21 @@ static InterpretResult run()
             break;
         }
         case OP_RETURN:
-            return INTERPRET_OK;
+        {
+            Value result = pop();
+
+            if (--vm.frame_count == 0)
+            {
+                pop();
+                return INTERPRET_OK;
+            }
+
+            vm.stack_top = frame->slots;
+            push(result);
+
+            frame = &vm.frames[vm.frame_count - 1];
+            break;
+        }
         }
     }