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

[John Millikin]

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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