Scott Lawrence <[email protected]> писал(а) в своём письме Tue, 31 May 2011
23:29:49 +0300:
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.
Oh, sorry. I was unclear. I have meant "assuming IO is lazy", as Yves
wrote.
And saying "some hacks" I meant unsafeInterleaveIO, which lies beneath the
laziness of, for example, getContents.
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