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

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 wrote:

Viktor Dukhovni writes:

...

...

On May 27, 2019, at 1:07 AM, Magicloud Magiclouds 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.