[Haskell-cafe] Reifying case expressions [was: Re: On stream processing, and a new release of timeplot coming]

[Brent Yorgey]

On Mon, Dec 26, 2011 at 12:32:13PM +0400, Eugene Kirpichov wrote:
> 2011/12/26 Gábor Lehel <illissius at gmail.com>
> 
> > On Sun, Dec 25, 2011 at 9:19 PM, Eugene Kirpichov <ekirpichov at gmail.com>
> > wrote:
> > > Hello Heinrich,
> > >
> > > Thanks, that's sure some food for thought!
> > >
> > > A few notes:
> > > * This is indeed analogous to Iteratees. I tried doing the same with
> > > Iteratees but failed, so I decided to put together something simple of my
> > > own.
> > > * The Applicative structure over this stuff is very nice. I was thinking,
> > > what structure to put on - and Applicative seems the perfect fit. It's
> > also
> > > possible to implement Arrows - but I once tried and failed; however, I
> > was
> > > trying that for a more complex stream transformer datatype (a hybrid of
> > > Iteratee and Enumerator).
> > > * StreamSummary is trivially a bifunctor. I actually wanted to make it an
> > > instance of Bifunctor, but it was in the category-extras package and I
> > > hesitated to reference this giant just for this purpose :) Probably
> > > bifunctors should be in prelude.
> >
> > Edward Kmett has been splitting that up into a variety of smaller
> > packages, for instance:
> >
> > http://hackage.haskell.org/package/bifunctors
> 
> Actually it's not a bifunctor - it's a functor in one argument and
> contrafunctor in the other.
> Is there a name for such a structure?

"Bifunctor" is usually used for such things as well.  Data.Bifunctor
only covers bifunctors which are covariant in both arguments.

-Brent