[Haskell-cafe] Re: :t main
simonpj at microsoft.com
Tue Dec 6 05:15:34 EST 2005
I've not been following this thread, but I wanted to check: you do know
about Tarmo Uustalu's stuff about comonads, don't you?
http://www.cs.helsinki.fi/u/ekarttun/comonad/ summarises (link to "The
essence of dataflow programming" at the bottom)
| -----Original Message-----
| From: haskell-cafe-bounces at haskell.org
[mailto:haskell-cafe-bounces at haskell.org] On Behalf Of
| David Menendez
| Sent: 06 December 2005 07:13
| To: Scherrer, Chad
| Cc: haskell-cafe at haskell.org
| Subject: RE: [Haskell-cafe] Re: :t main
| Scherrer, Chad writes:
| > > From: Cale Gibbard [mailto:cgibbard at gmail.com]
| > > See:
| > > http://haskell.org/pipermail/haskell-cafe/2003-January/003794.html
| > >
| > > The OI comonad as previously envisioned breaks referential
| > > transparency. I/O just doesn't seem to be something which one
| > > can easily do comonadically, since once coeval/extract is
| > > applied, you're back to plain values, and there's no
| > > imposition of sequencing.
| > >
| > > - Cale
| > Hmm, I hadn't seen that. The asymmetry is pretty frustrating in that
| > case.
| > After poking around a bit more, I (re)discovered some discussion of
| > this on Hawiki:
| > http://www.haskell.org/hawiki/CoMonad
| > After reading Dave Menendez's comments, I'm wondering...
| > If we consider
| > IO a = Realworld -> (Realworld, a)
| > then wouldn't we dually have something like
| > OI a = (Realworld, Realworld -> a)?
| > Could this be what screws things up? Right now it seems like OI is
| > acting like it has the same type as IO, with a different name.
| Aside from the product comonad and the exponent (reader) monad, I
| think we'll find much overlap between monad and comonad functionality.
| It's been said that monads describe effects that propagate outwards,
| whereas comonads describe effects that propagate inwards.
| My guess is that comonadic IO would look more like dataflow
| David Menendez <zednenem at psualum.com> | "In this house, we obey the
| <http://www.eyrie.org/~zednenem> | of thermodynamics!"
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