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.htm... [2] http://www.cs.cmu.edu/~neelk/pattern-popl09.pdf