Martijn van Steenbergen wrote:
Hello,
Mr. McBride and mr. Paterson define in their Applicative paper:
data Except e a = OK a | Failed e instance Monoid e => Applicative (Except e) where ...
Sometimes I'd still like to use >>= on Excepts but this "feels" wrong somehow, because it doesn't use monoids nicely like the Applicative instance does. Are there any good reasons such a Monad instance shouldn't be defined? Does it violate any laws, for example?
Thanks,
Martijn. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
I'm sure you could, but then ap /= (<*>). This seems related to a question that I once asked http://www.haskell.org/pipermail/haskell-cafe/2009-January/054139.html -- Tony Morris http://tmorris.net/