Personally, I love Haskell (as a hobby / pet language) for the ability to express myself very naturally and mathematically (or functionally, if you will), compared to the more imperative way of implementing the functions at a "lower level", so to speak. To design algorithms and leave the implementation to the compiler, perhaps? Sure, this won't win any awards in a fight against say, highly-optimized C or assembly-code that is specifically crafted against this particular problem- but the higher abstraction levels allow excellent readability for potential future lookenspeepers who might make minute changes to complete a task somewhat similar yet different in details. And who knows - maybe in the near future we might have even smarter compilers which could optimize the implementation to have less recomputations? We already have the magic of laziness today :)