lots o fixes

internal/builtins/builtins.go

@@ -11,6 +11,7 @@ var Builtins = map[string]object.Builtin{
 	"len":       {Name: "len", Fn: Len},
 	"input":     {Name: "input", Fn: Input},
 	"print":     {Name: "print", Fn: Print},
+	"println":   {Name: "println", Fn: Println},
 	"first":     {Name: "first", Fn: First},
 	"last":      {Name: "last", Fn: Last},
 	"rest":      {Name: "rest", Fn: Rest},

internal/builtins/print.go

@@ -16,7 +16,21 @@ func Print(args ...object.Object) object.Object {
 		return newError(err.Error())
 	}
 
-	fmt.Println(args[0].String())
+	fmt.Fprint(object.Stdout, args[0].String())
+
+	return nil
+}
+
+// Println ...
+func Println(args ...object.Object) object.Object {
+	if err := typing.Check(
+		"println", args,
+		typing.MinimumArgs(1),
+	); err != nil {
+		return newError(err.Error())
+	}
+
+	fmt.Fprintln(object.Stdout, args[0].String())
 
 	return nil
 }