[Haskell-cafe] Lazy Evaluation in Monads

[Yves Parès]

No, I think Artyom meant "assuming IO is lazy".
He intended to show that, indeed, it is not, or else side-effects would
never be performed


2011/5/31 Scott Lawrence <bytbox at gmail.com>

> On 05/31/2011 04:20 PM, Artyom Kazak wrote:
> > Suppose iRecurse looks like this:
> >   iRecurse = do
> >     x <- launchMissiles
> >     r <- iRecurse
> >     return 1
> >
> > As x is never needed, launchMissiles will never execute. It obviously is
> > not what is needed.
>
> Prelude> let launchMissiles = putStrLn "UH OH" >> return 1
> Prelude> let iRecurse = launchMissiles >> return 1
> Prelude> iRecurse
> UH OH
> 1
> Prelude>
>
> Looks like launchMissiles /does/ execute, even though x is (obviously)
> never needed.
>
>
>
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