[Haskell-cafe] How to make boolean logic with IO Monad more expressive?

[Magicloud Magiclouds]

With side effect, they are not the same.

Viktor's nested-if does not trigger unnecessary IO action, while liftA2 does.

On Mon, May 27, 2019 at 5:38 PM Jack Kelly <jack at jackkelly.name> wrote:
>
> Viktor Dukhovni <ietf-dane at dukhovni.org> writes:
>
> >> On May 27, 2019, at 1:07 AM, Magicloud Magiclouds <magicloud.magiclouds at gmail.com> wrote:
> >>
> >> ```
> >> status <- ioOperation -- IO-ed anyway
> >> return $ pureComputing || (status && pure2)
> >> ```
> >
> > With two helpers:
> >
> >   (<&&>) :: IO Bool -> IO Bool -> IO Bool
> >   (<&&>) ma mb = ma >>= (\a -> if not a then return False else mb)
> >
> >   (<||>) :: IO Bool -> IO Bool -> IO Bool
> >   (<||>) ma mb = ma >>= (\a -> if a then return True else mb)
>
> These generalise to any Applicative, I think:
>
> import Control.Applicative (liftA2)
>
> (<&&>) = liftA2 (&&)
> (<||>) = liftA2 (||)
>
> -- Jack
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.