seperated builtins

object/builtin_first.go

@@ -0,0 +1,20 @@
+package object
+
+// First ...
+func First(args ...Object) Object {
+	if len(args) != 1 {
+		return newError("wrong number of arguments. got=%d, want=1",
+			len(args))
+	}
+	if args[0].Type() != ARRAY_OBJ {
+		return newError("argument to `first` must be ARRAY, got %s",
+			args[0].Type())
+	}
+
+	arr := args[0].(*Array)
+	if len(arr.Elements) > 0 {
+		return arr.Elements[0]
+	}
+
+	return nil
+}