Hi
I'm currently in the process of attempting to write such a thing...
Good luck! Haskell needs more implementations to retain its purity and compatibility.
What is the value of show [] ?
That is indeed a difficult point. Since I want an interpreter so I can step through the code interactively, I was just going to make the interpreter *ask* me which implementation to call...
Yuk! I couldn't think of a better answer, which is what stopped me from writing such an evaluator.
On the other hand, parsing Haskell input is intractably hard. Whitespace actually matters, which makes the program to parse Haskell horrendusly complex. Several times I've been forced to give up due to the sheer complexity of it all.
Why not just reuse the standard Haskell parser? Its in Hacle (google keyword: Hacle) amongst other places. It parses all of Haskell, and is pretty easy to use. Thanks Neil