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 :-)

Thanks,

G