[Haskell-beginners] How to create a monad in GHC 7.10 or newer

[Ahmad Ismail]

Thank you very much.

*Thanks and Best Regards,Ahmad Ismail*


On Sun, Nov 13, 2022 at 9:22 PM Francesco Ariis <fa-ml at ariis.it> wrote:

> Il 13 novembre 2022 alle 20:56 Ahmad Ismail ha scritto:
> > How can I fix it so that `ItDoesnt <*> WhatThisIsCalled` works?
> >
> > I have came up with a solution without WhatThisIsCalled
> >
> > data WhoCares a = ItDoesnt | Matter a deriving (Eq, Show)
> >
> > instance Functor WhoCares where
> >     fmap _ ItDoesnt = ItDoesnt
> >     fmap f (Matter a) = Matter (f a)
> >
> > instance Applicative WhoCares where
> >     pure = Matter
> >     Matter f <*> Matter a = Matter (f a)
> >     ItDoesnt <*> _ = ItDoesnt
> >     _ <*> ItDoesnt = ItDoesnt
> >
> > instance Monad WhoCares where
> >     return x = Matter x
> >     (Matter x) >>= k = k x
> >     ItDoesnt >>= _ = ItDoesnt
>
> This makes much more sense. Now <*> is total and >>= is meaningful,
> well done!
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