I've been working on a "ListT done right" for submission into `transformers`. I could split it off into its own package, but I would like to first run it by you all, particularly Ross, to see if this can be included this in `transformers` because I feel that `transformers` is where this belongs. I've lpasted the implementation here: http://lpaste.net/90890 I've written it to follow the spirit of the `transformers` library as closely as possible, both in API, documentation, and source code style. I'm fine with either replacing the old `ListT` implementation or providing both. I'll leave it to you guys to make the call on that. As long as the correct version is in `transformers` somewhere then I'm happy. If I *had* to pick a side, I suppose I would favor replacing the old one. Also, any suggestions for changes are welcome, particularly if they improve the likelihood of this getting into `transformers`.