Thinking of stacks, I've often wondered if Haskell would be a good language for implementing a PostScript interpreter.

I actually have the beginning of a PostScript interpreter somwhere... And the core of a Joy interpreter is extremely small. It's pretty much 'foldl compose . map interpretWord'. Of course, I implemented a Joy interpreter in the slightly sugared lambda calculus that lambdabot's @eval module supports so... (Crap, I actually want to find it (the PostScript interpreter) now.)