On Sat, Dec 24, 2011 at 2:00 PM, Erik de Castro Lopo <mle...@mega-nerd.com> wrote: > Michael Craig wrote: > >> I've been looking for a way to compose enumeratees in the enumerator >> package, but I've come up with nothing so far. I want this function >> >> (=$=) :: Monad m => Enumeratee a0 a1 m b -> Enumeratee a1 a2 m b -> >> Enumeratee a0 a2 m b > > I think part of the problem here is that Enumeratee is defined as: > > type Enumeratee ao ai m b = Step ai m b -> Iteratee ao m (Step ai m b) > > If you expand out your type signature you get: > > (=$=) :: Monad m > => (Step a1 m b -> Iteratee a0 m (Step a1 m b)) > -> (Step a2 m b -> Iteratee a1 m (Step a2 m b)) > -> (Step a2 m b -> Iteratee a0 m (Step a2 m b)) > > which to me looks rather painful to implement. > >> I've been looking at the iterIO package as a possible alternative, because >> it seems to allow easy composition of Inums (enumeratees). I'm a little >> skittish of it because it seems unpopular next to enumerator. >> >> Thoughts on these issues? > > I think these issues are actually common to all implementations of > the Iteratee concept. Basically they do not compose as nicely and > as cleanly as they would be expected to. I recently ran into this > difficulty in composition in my project which was solved by nesting > an iteratee inside an enumerator. > > > https://github.com/erikd/http-proxy/commit/73775555c1cc695b21b7c13b823abc6c3358a978 > > There is work being done to address these issues. See Michael > Snoyman's work on Conduits: > > https://github.com/snoyberg/conduit > > Cheers. > Erik > -- > ---------------------------------------------------------------------- > Erik de Castro Lopo > http://www.mega-nerd.com/ > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe
By the way, conduit defines *precisely* that operator, for "fusing" (iterIO's term) two conduits together. Michael _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
