On 15/12/2010 04:01, Jonathan Geddes wrote:
Fail can't just be removed. That would just break too much code. For
example, I find myself writing code like the following:
[a,b,c]<- Just someList
in place of
let [a,b,c] = someList
so that pattern match failure is "lifted" into the maybe monad (as
long as I'm already in the maybe monad).
I would like to see a MonadFail class, with one method 'fail', such
that it is a compile-time error to try 'failable' pattern matches in a
monad that is not an instance of MonadFail.
--Jonathan
Perhaps pattern match failures in a MonadPlus should bind to mzero - I believe that this is what your example and
similar wish to achieve.
I've updated http://haskell.org/haskellwiki/Functor-Applicative-Monad_Proposal to mention this. Does anyone know why
fail and Pointed (in the paragraph "This would eliminate...") aren't beginning a new paragraph? They are both preceded
by a blank line in the wiki source.
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