iteratee Couple functions for combining Enueratees with Enumerators and Iteratees

[Michael Baikov]

One more version, clean on typelevel and without unsafeCoerce


($=) :: (Nullable s1, Nullable s2, Monad m) => (forall a. Enumerator
s1 m a) -> Enumeratee s1 s2 m b -> Enumerator s2 m b
($=) enum enee iter = enum (enee iter) >>= run


On Fri, Nov 25, 2011 at 2:14 PM, Michael Baikov <manpacket at gmail.com> wrote:
> Currently we have two nice functions for combining Enumeratees ><> and
> <>< which can be used to produce chains of Enumeratees. I think that
> it will be nice to have those functions as well:
>
>
> -- this implementation relies on unsafeCoerce to keep type signature
> nice and clean
> -- so it is requred to import Unsafe.Coerce
>
> --| Combines Enumerator which produces stream of s and Enumeratee
> which transforms stream of s to stream
> -- of s' to into Enumerator which produces stream of s'
> ($=) :: (Nullable s, Nullable s', Monad m) => Enumerator s m a ->
> Enumeratee s s' m b -> Enumerator s' m b
> ($=) enum enee iter = (unsafeCoerce enum) (enee iter) >>= run
>
>
>
> -- this implementation leaves type signature a bit messy, but without
> using unsafeCoerce
>
> --| Combines Enumerator which produces stream of s and Enumeratee
> which transforms stream of s to stream
> -- of s' to into Enumerator which produces stream of s'
> ($=) :: (Nullable s, Nullable s', Monad m) => Enumerator s m (Iteratee
> s' m a) -> Enumeratee s s' m a -> Enumerator s' m a
> ($=) enum enee iter = enum (enee iter) >>= run
>
>
> --| Combines Enumeratee from s to s' and Iteratee which consumes s' to
> into Iteratee which consumes s
> (=$) :: (Nullable s, Nullable s', Monad m) => Enumeratee s s' m a ->
> Iteratee s' m a -> Iteratee s m a
> (=$) = (.) joinI
>
>
> (=$) is mostly to keep sources clean, but ($=) can be used to
> enumerate any given Iteratee over list of several different data
> sources
> (but type of the source can be transformed to type of Iteratee using
> Enumeratee) just by transforming them to a single type and performing
> foldM.
>