It sounds like the semantics of the MonadPlus methods are under-specified. I recall once writing a newtype wrapper to treat the same non-determinism monad with different mplus semantics, akin to cut versus backtracking.
I think of MonadPlus as a less expressive version of msplit, from Backtracking, Interleaving, and Terminating Monad Transformers The Functional Pearl paper by Oleg Kiselyov, Chung-chieh Shan, Daniel P. Friedman and Amr Sabry. ICFP 2005. Is that an over-simplification? On Fri, May 9, 2008 at 3:12 PM, Bryan O'Sullivan <[EMAIL PROTECTED]> wrote: > Andrew Coppin wrote: > >> ...so it's a kind of choice operator? Run all actions until you get to >> one that succeeds and return the result from that? > > In the context of Parsec, yes. In the grander scheme of things, the > behaviour depends on whatever is appropriate for the particular monad > you're working in. > > So, for example, mplus for lists is (++) and mzero is [], which is quite > a different set of behaviours from the Parsec case. Usually, you can > rely on MonadPlus behaving like a monoid. There are occasional > exceptions, which is a mite upsetting. > > http://www.haskell.org/haskellwiki/MonadPlus > > <b > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
