Re: [Haskell-cafe] [Haskell] Functor => Applicative => Monad

Hello, I think that we should make both changes (make Applicative a super-class of Monad, and remove the "fail" method from Monad). Code will break but we can fix it. By the way, just for reference, the proposal to have a separate failure class and using it in the "do" notation, is how things used to be back in Haskell 1.4 (one version before Haskell 98). For the curious, take a look at page 21 of http://haskell.org/definition/haskell-report-1.4.ps.gz -Iavor On Thu, Dec 16, 2010 at 3:57 PM, Lennart Augustsson wrote:

IO

On Thu, Dec 16, 2010 at 6:03 PM, John Smith wrote:

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On 15/12/2010 14:31, Lennart Augustsson wrote:

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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?

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