Collecting values from Functors?
Fri, 6 Jun 2003 20:52:57 +0200
> class FunctorM t where
> fmapM :: Monad m => (a -> m b) -> (t a -> m (t b))
> fmapM_ :: Monad m => (a -> m b) -> (t a -> m ())
> fmapM_ f t = fmapM f t >> return ()
The `fmapM' function is also known as a monadic map. It can be
defined in a generic way for every Haskell data type. It's in
the library of Generic Haskell (called mapMl):
As an aside, gmap and friends won't fit the bill, as they work
on types rather than functors.