[Haskell-cafe] [Haskell] Functor => Applicative => Monad
aslatter at gmail.com
Thu Dec 16 21:54:19 CET 2010
On Thu, Dec 16, 2010 at 12:03 PM, John Smith <voldermort at hotmail.com> wrote:
> On 15/12/2010 14:31, Lennart Augustsson wrote:
>> Yes, I think there should be a MonadFail distinct from MonadPlus.
>> Some types, like IO, are not in MonadPlus, but have a special
>> implementation of the fail method.
>> Personally, I think fail should just be removed, but that would break
>> existing code.
>> The fail method was introduced for the wrong reasons (better error
>> messages was the excuse).
> Which other monads (other than MonadPlus subclasses) define fail?
STM is in MonadPlus, but I don't think pattern-match failure should be
the same as STM.retry.
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