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

11 Dec 2014

      Well, in this case I'd use the actual bind (>>=) and write

   view sectors >>= do
     traverse $ \ s ->
       case s of
         Sector{...} -> liftIO $ do
           sectorDrawWalls
           ... more code ...
         ... maybe more cases ...

Killed the long-ranging parentheses!  Haskell rules! ;-)

Cheers,
Andreas

On 11.12.2014 11:59, 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. ;)
-- ocharles
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Andreas Abel  <><      Du bist der geliebte Mensch.

Department of Computer Science and Engineering
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