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

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] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH