[Haskell-cafe] Why were unfailable patterns removed and "fail" added to Monad?

Ryan Ingram ryani.spam at gmail.com
Fri Jan 20 20:34:03 CET 2012

I don't currently have anything to add to this discussion, but I want to
encourage you all to keep having it because I think it has potential to
improve the language in the "do things right or don't do them at all"
philosophy that Haskell tends towards.

  -- ryan

On Fri, Jan 20, 2012 at 6:32 AM, Jacques Carette <carette at mcmaster.ca>wrote:

> On 19/01/2012 10:19 PM, Edward Z. Yang wrote:
>>  In other words,
>> MonadZero has no place in dealing with pattern match failure!
>>  I completely agree.  See "Bimonadic semantics for basic pattern matching
> calculi" [1] for an exploration of just that.  In the language of that
> paper, the issue is that there is a monad of effects for actions, and a
> monad of effects for pattern matching, and while these are very lightly
> related, they really are quite different.  By varying both monads, one can
> easily vary through a lot of different behaviour for pattern-matching as
> found in the literature.
> I should add that if we had known about some of the deeper structures of
> pattern matching (as in Krishnaswami's Focusing on Pattern Matching [2],
> published 3 years *later*), we could have simplified our work.
> Jacques
> [1] http://www.cas.mcmaster.ca/~**kahl/Publications/Conf/Kahl-**
> Carette-Ji-2006a.html<http://www.cas.mcmaster.ca/%7Ekahl/Publications/Conf/Kahl-Carette-Ji-2006a.html>
> [2] http://www.cs.cmu.edu/~neelk/**pattern-popl09.pdf<http://www.cs.cmu.edu/%7Eneelk/pattern-popl09.pdf>
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