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

Magicloud Magiclouds writes:

With side effect, they are not the same. Viktor's nested-if does not trigger unnecessary IO action, while liftA2 does.

Ah, of course. Still, there's no need to restrict their type to IO; any Monad should be fine. -- Jack

On Mon, May 27, 2019 at 5:38 PM Jack Kelly wrote:

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Viktor Dukhovni writes:

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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 (||)