rearrange builtins

builtins/int.go

@@ -0,0 +1,31 @@
+package builtins
+
+import "monkey/object"
+
+import "strconv"
+
+// Int ...
+func Int(args ...object.Object) object.Object {
+	if len(args) != 1 {
+		return newError("wrong number of arguments. got=%d, want=1", len(args))
+	}
+
+	switch arg := args[0].(type) {
+	case *object.Boolean:
+		if arg.Value {
+			return &object.Integer{Value: 1}
+		}
+		return &object.Integer{Value: 0}
+	case *object.Integer:
+		return arg
+	case *object.String:
+		n, err := strconv.ParseInt(arg.Value, 10, 64)
+		if err != nil {
+			return newError("could not parse string to int: %s", err)
+		}
+
+		return &object.Integer{Value: n}
+	default:
+		return newError("argument to `int` not supported, got=%s", args[0].Type())
+	}
+}