Re: [Haskell-cafe] How to understand `|` in this code snippet ?

27 Feb 2010

      On Sat, Feb 27, 2010 at 05:08:18PM -0800, zaxis wrote:
...
Then can i change it to :
case timeout of
        Just str -> do
            [(t, _)] <- reads str
            addTimeout t (hPutStrLn stderr "*** TIMEOUT" >> _exit 1)
            return ()
        _ -> return ()
No, that's different.  You could change it to:

case timeout of
  Just str -> case reads str of
    [(t, _)] -> do addTimeout t (hPutStrLn stderr "*** TIMEOUT" >> _exit 1)
    	     	   return ()
    _        -> other -- (1)
  _        -> other -- (2)
where other = return ()

The cases (1) and (2) are the same and simulate the fact that
when the pattern guard fails, then execution falls to the next
case.

Of course you could just write

case fmap (reads str) timeout of
  Just [(t, _)] -> ...
  _             -> ...

HTH,

--
Felipe.

Re: [Haskell-cafe] How to understand `|` in this code snippet ?

Felipe Lessa