Even aside from support pretty unit testing, having a good tool for automating the generation of test cases makes a world of difference. http://www.haskell.org/

Even aside from support pretty unit testing, having a good tool for automating the generation of test cases makes a world of difference. http://www.haskell.org/haskellwiki/Introduction_to_QuickCheck http://www.haskell.org/haskellwiki/Introduction_to_QuickChec... for example is a great tool that allows for pretty expressive specifications and counter example generation