[Haskell-beginners] getopt

Gaius Hammond gaius at gaius.org.uk
Thu Aug 5 15:18:16 EDT 2010

Hi all,

I have used GetOpt in Python and Ocaml so I am reasonably familiar  
with it, and I have been studying the technique here:


Can anyone explain to me what is actually happening here:

     opts <- foldl (>>=) (return startOptions) actions

     let Options { optVerbose = verbose
                 , optInput = input
                 , optOutput = output   } = opts
     input >>= output

I understand the fold is evaluating everything in the actions list  
overlaying them onto the startOptions record, then getting these out  
of IO and into the opts record - but where are "verbose", "input" and  
"output" coming from? Are they just aliases?

Any insight gratefully received :-)



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