Generating unique labels ...

[Reto Kramer]

I'm trying to create a function (using ghc 5.04.2) that returns a 
unique string label each time it's called (unique w.r.t. the program 
run).  Using the system timer doesn't cut it (too coarse and hence not 
unique).

The challenge is that I'm using Strafunsky to traverse a syntax tree 
and rewrite expression nodes, so I cannot "thread" a counter all 
through this existing library, but need some "side-effecting" store 
that I can update.

Any suggestions to such a basic question?

- Reto