Stephen Tetley wrote:
John Lato wrote:
This is how I think of them. I particularly your description of them as a foldl with a "pause" button. Maybe it would be helpful to consider iteratees along with delimited continuations?
Aren't they closer - in implementation and by supported operations - to resumptions monads?
See many papers by William Harrison here: http://www.cs.missouri.edu/~harrisonwl/abstracts.html
A general method to implement resumption monads, or, in fact, any monad, is given in my "Operational Monad Tutorial": http://apfelmus.nfshost.com/articles/operational-monad.html Here a tiny toy implementation of Iteratees: data IterateeI a where Symbol :: IterateeI Char EOF :: IterateeI Bool type Iteratee = ProgramT IterateeI symbol = singleton . Symbol eof = singleton . EOF runString :: Monad m => Iteratee m a -> String -> m a runString m cs = go cs =<< viewT m where go _ (Return x) = return x go [] (Symbol :>>= k) = error "Expecting input" go (c:cs) (Symbol :>>= k) = runString (k c) cs go cs (EOF :>>= k) = runString (k $ null cs) cs -- an iteratee that counts the number of elements in the input count :: Monad m => Iteratee m Int count = go 0 where go n = eof >>= \b -> case b of True -> return n False -> symbol >> go $! (n+1) Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com