builtins

evaluator/builtins.go

@@ -0,0 +1,21 @@
+package evaluator
+
+import "monkey/object"
+
+var builtins = map[string]*object.Builtin{
+	"len": &object.Builtin{
+		Fn: func(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.String:
+				return &object.Integer{Value: int64(len(arg.Value))}
+			default:
+				return newError("argument to `len` not supported, got %s", args[0].Type())
+
+			}
+		},
+	},
+}