On Fri, Jul 15, 2011 at 03:01:59PM +0100, Guido Trotter wrote: > On Fri, Jul 15, 2011 at 2:00 PM, Iustin Pop <ius...@google.com> wrote: > > > Mmm, I can fmap this to make it even more clear: > > > > fmap (flip (-1) 1) > > > > as Maybe is a functor instance, and we only need to work on the 'inside' > > value. > > Not sure this is clear to me. Feel free to apply it this way though. > Any explanation or nice references? :)
Well, the basic idea is that it bothers me to use "maybe Nothing (Just . fn)" which does exactly the same thing as "fmap fn" :) maybe Nothing (Just . fn) means that if the value is nothing, you don't do anything, and if it's a Just something, you unpack it, then apply fn, then pack it again in a Maybe. Which is exactly what fmap is supposed to do - apply a transformation on the value inside the container (if there is any). http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.html#t:Functor Not sure if that is enough explanation, just that "it makes sense" to use the proper abstraction here… > > Not really, as the mutation function would be too unreadable? > > > > maybe (False, Nothing) (\n -> n <= ixes_cnt, Just (n - ixes_cnt)) limit > > > > Not too bad, I can read it, but feel free to live it the other way if > you prefer. Will do that, thanks. iustin
