Then can i change it to :
case timeout of
Just str -> do
[(t, _)] <- reads str
addTimeout t (hPutStrLn stderr "*** TIMEOUT" >> _exit 1)
return ()
_ -> return ()
Sincerely!
Brandon S. Allbery KF8NH wrote:
>
> On Feb 27, 2010, at 04:07 , zaxis wrote:
>>
>> xxxMain = do
>> timeout <- getEnv "xxx_TIMEOUT"
>> case timeout of
>> Just str | [(t, _)] <- reads str -> do
>> addTimeout t (hPutStrLn stderr "*** TIMEOUT" >> _exit 1)
>> return ()
>> _ -> return ()
>> .......
>>
>> What does the `|` mean in "Just str | [(t, _)] <- reads str" ?
>> Is it a logical `or` ?
>
> It's a guard. Same as with function definitions (in fact, function
> definitions of that form are converted to case expressions).
>
> --
> brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com
> system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu
> electrical and computer engineering, carnegie mellon university KF8NH
>
>
>
>
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>
>
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fac n = let { f = foldr (*) 1 [1..n] } in f
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