[Haskell-cafe] How to understand such a `case` ?

[zaxis]

thanks for your quick answer ! Then what's the advantage using such a `case`
not using `if` statement given by you ?   For me, the `if` statement is more
clear .


jmillikin wrote:
> 
> Sorry; forgot to CC the list
> 
> That case is equivalent to:
> 
> if filex
>    then return $ Just $ file  x
>    else if filex'
>        then return $ Just $ file' x
>        else findHelper xs
> 
> 
> The specific syntax being used is called a "pattern guard":
> http://www.haskell.org/haskellwiki/Pattern_guard
> 
> On Tue, Dec 8, 2009 at 16:59, zaxis <z_axis at 163.com> wrote:
>>
>> findHelper (x:xs) = do -- not lazy, but that's not really important here
>>        filex  <- fileExists (file  x)
>>        filex' <- fileExists (file' x)
>>        case () of
>>            _
>>                | filex     -> return $ Just $ file  x
>>                | filex'    -> return $ Just $ file' x
>>                | otherwise -> findHelper xs
>>    file  x = foldl1 joinFileName (x ++ [helper])
>>    file' x = (file x) ++ (getConfig "exe_ext")
>>
>> Sincerely!
>>
>> -----
>> fac n = foldr (*) 1 [1..n]
>> --
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>>
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-----
fac n = foldr (*) 1 [1..n]
-- 
View this message in context: http://old.nabble.com/How-to-understand-such-a-%60case%60---tp26703526p26703743.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.