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

[zaxis]

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` ? 

Sincerely!



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fac n = let {  f = foldr (*) 1 [1..n] } in f 
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