type checking and error handling for builtins improved.

builtins/print.go

@@ -1,14 +1,23 @@
 package builtins
 
-import "monkey/object"
+import (
+	"monkey/object"
+	"monkey/typing"
+)
 
 import "fmt"
 
 // Print ...
 func Print(args ...object.Object) object.Object {
-	for _, arg := range args {
-		fmt.Println(arg.String())
+	if err := typing.Check(
+		"print", args,
+		typing.MinimumArgs(1),
+		typing.WithTypes(object.STRING_OBJ),
+	); err != nil {
+		return newError(err.Error())
 	}
 
+	fmt.Println(args[0].String())
+
 	return nil
 }