On Thu, Jun 05, 2003 at 09:08:03AM +1200, Tom Pledger wrote: > | I am sorry, I misunderstood the problem. > > You're too modest. :-) > > There *is* a solution in that direction.
Yes, I knew I could use a State monad or a Writer monad, but I thought that it would be an overkill. Fold is more appropriate here. > Here's my version of fmapM, which was inspired by something in Tim > Sheard's paper "Generic Unification via Two-Level Types and > Parameterized Modules". > > import Control.Monad.State > > -- ------------------------------------------------------------ > -- Functors through which monads may be lifted > > class Functor f => FunctorSeq f where > fseq :: Monad m => f (m a) -> m (f a) > > instance FunctorSeq [] where > fseq = sequence > > instance FunctorSeq Maybe where > fseq Nothing = return Nothing > fseq (Just mx) = do x <- mx; return (Just x) > > fmapM :: (Monad m, FunctorSeq f) => (a -> m b) -> f a -> m (f b) > fmapM f xs = fseq (fmap f xs) > > fseq2list :: (FunctorSeq f) => f a -> [a] > fseq2list fa > = reverse (execState (fmapM (\a -> modify (a:)) fa) []) I like this solution. The fseq function seems to be more general. > Regards, > Tom Regards, Tom :) -- .signature: Too many levels of symbolic links _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
