Re: bind :: Monad m => (a -> m b) -> m a -> m b

11 Dec 2014


      On 11-12-2014 08:59, Oliver Charles wrote:
...
Many people seem to be suggesting that this isn't a useful function to
have, but I just found myself wanting it for a pattern that I write a
lot. The code in question is:
traverse
        (\s ->
           case s of
             Sector{..} ->
               liftIO (do sectorDrawWalls
                          sectorDrawFloor
                          sectorDrawCeiling))
        =<< view sectors
That is, I want to traverse some sort of structure, and the structure
that I want to traverse itself comes from performing a monadic
action. Imo, this would be more readable as
bind (traverse (\s ->
                    case s of
                      Sector{..} ->
                        liftIO (do sectorDrawWalls
                                   sectorDrawFloor
                                   sectorDrawCeiling)))
       (view sectors)
Whatever we call it, I do feel it has use -- `traverse f =<< m` comes up
a lot, but with a complex f, using =<< or >>= leads to less
readability. Maybe I spend too much time with Chris. ;)
Since you didn't mention, I'm going to point out that you already can use:
...
(=<<) (traverse (\s ->
                    case s of
                      Sector{..} ->
                        liftIO (do sectorDrawWalls
                                   sectorDrawFloor
                                   sectorDrawCeiling)))
       (view sectors)
The infix vs prefix discussion looks like a red herring.  This proposal
is only about using the letters `bind` instead of the symbols `(=<<)`.
Which, besides "not being letters", I can only think of "it has 5 chars
instead of 4, messing with my indentation" as disadvantages.

Cheers,

-- 
Felipe.

Re: bind :: Monad m => (a -> m b) -> m a -> m b

Felipe Lessa