Re: Collecting values from Functors?

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): http://www.cs.uu.nl/research/projects/generic-haskell/ As an aside, gmap and friends won't fit the bill, as they work on types rather than functors. Cheers, Ralf