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

[Emil Axelsson]

Not with the standard `||` and `&&` operations. You'd have to define new 
versions with a `Monad` constraint.

The `monad-loops` package is pretty nice for short-circuiting stuff. 
See, for example, `andM` and `orM`. But it doesn't provide any binary 
operators.

https://hackage.haskell.org/package/monad-loops

/ Emil

Den 2019-05-27 kl. 07:07, skrev Magicloud Magiclouds:
> Hi,
>
> I think `a || b && c` is more clear than
> ```
> if a
>    then True
>    else if b
>      then if c
>        then True
>        else False
>      else False
> ```
>
> And some languages, `pureComputing || (ioOperation && pure2)` involves
> IO only when pureComputing is False.
>
> So in Haskell, is it possible to get both benefits?
> ```
> status <- ioOperation -- IO-ed anyway
> return $ pureComputing || (status && pure2)
> ```
> ```
> if pureComputing
>    then return True
>    else do
>      status <- ioOperation
>      if status
>        then return pure2
>        else return False
> -- Looks ugly
> ```
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