vincent:
i see that the definition of fix (from Control.Monad.Fix) could not be any simpler:
fix f = let x = f x in x
same goes for the type:
Prelude> :t Control.Monad.Fix.fix Control.Monad.Fix.fix :: (a -> a) -> a
it's just that i find it difficult to get concrete intellectual mileage out of it. i can reproduce results for specific examples (and even manipulate them a bit), but feel like i'm missing something deep yet simple. say, i would not know where and how to apply it. so obviously true understanding is still missing. reminds me of my first encounters with $H \psi = E \psi$. ;-)
most likely, i should just more carefully read the references i cited myself ;-)
anyhow. if someone has a "pedestrian's guide to the fixed point operator" lying around, a link would be much appreciated.
I use it when I need a local loop expression, maybe once every couple of months. A real world example from xmonad, f = fix $ \again -> do more <- checkMaskEvent d enterWindowMask ev when more again That is, keep sucking up X events till there's no 'more'. Of course, you can always just name your loop with 'where' and use that. f = go where go = do more <- checkMaskEvent d enterWindowMask ev when more go TMTOWTDI with recursion :-) -- Don