diff --git a/internal/internal.go b/internal/internal.go
new file mode 100644
index 0000000..23545ac
--- /dev/null
+++ b/internal/internal.go
@@ -0,0 +1,20 @@
+// Copyright 2018 The CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal // import "cuelang.org/go/internal"
+
+// TODO: refactor packages as to make this package unnecessary.
+
+// DebugStr prints a syntax node.
+var DebugStr func(x interface{}) string