type checking and error handling for builtins improved.

builtins/args.go

@@ -1,9 +1,19 @@
 package builtins
 
-import "monkey/object"
+import (
+	"monkey/object"
+	"monkey/typing"
+)
 
-// Args  ...
+// Args ...
 func Args(args ...object.Object) object.Object {
+	if err := typing.Check(
+		"args", args,
+		typing.ExactArgs(0),
+	); err != nil {
+		return newError(err.Error())
+	}
+
 	elements := make([]object.Object, len(object.Arguments))
 	for i, arg := range object.Arguments {
 		elements[i] = &object.String{Value: arg}