I believe type signatures are the very essence of Haskell documentation! I'd much rather see a program with type signatures for functions and little (or no) comments over programs with no type signatures and ambigious comments (if any comments at all!).
Okay, but when using a syntax directed editor, type signatures can be automatically provided because the types are known. Furthermore, IMHO, type signatures alone are not enough, a good parameter name says at least as much as the type. E.g. what does a function Int -> Int -> Bool do? I have no idea. A good function name helps, e.g. isDivisible:: Int -> Int -> Bool. But then I still don't know which parameter is the numerator and denominator. So good names for the parameters are at least as important, e.g. isDivisible :: numerator:Int -> denonimator:Int -> Bool
Type signatures really does make dealing with someone elses code that much easier.
Yes, as is good documentation, which unfortunately is still limited to ASCII. I would prefer to have rich documentation right inside my source code, with math symbols, drawings, pictures, animations, whatever... Cheers, Peter