[Haskell-beginners] getopt

[Stephen Tetley]

input, output and verbose are bindings introduced by pattern matching
within the let clause.

The Options datatype has field labels optVerbose, optInput and optOutput:

data Options = Options  { optVerbose    :: Bool
                        , optInput      :: IO String
                        , optOutput     :: String -> IO ()
                        }

Pattern matching can elide field labels, this let binding is equivalent:

 let (Options verbose input output) = opts