add file trace to parser, refactor, fix inner type

core/values.go

@@ -467,6 +467,31 @@ var ListPrototype = map[string]*BuiltinFunctionValue{
 		nil,
 		false,
 	},
+	"put": {
+		"put",
+		&FunctionSignature{
+			[]TypeSignature{
+				&NumberSignature{}, &InnerSignature{},
+			},
+			&NilSignature{},
+		},
+		func(_ *VM, this Value, args []Value) (Value, error) {
+			l := this.(*ListValue)
+			i := int(args[0].(*NumberValue).Number)
+			v := args[1]
+
+			// bounds check
+			if i < 0 || i >= len(l.Items) {
+				return nil, errors.New(fmt.Sprintf("index %x out of range", i))
+			}
+
+			l.Items[i] = v
+
+			return &NilValue{}, nil
+		},
+		nil,
+		false,
+	},
 	"length": {
 		"length",
 		&FunctionSignature{