[Haskell-cafe] Writing an 'expect'-like program with runInteractiveCommand

Graham Fawcett graham.fawcett at gmail.com
Thu May 1 16:40:13 EDT 2008

Hi folks,

I would like to communicate with an external, line-oriented process,
which takes a sequence of one-line commands, each returning an
arbitrary number of lines, and waits for another command after each
response.  So, something like:

sendCmd :: (Handle, Handle) -> String -> IO [String]

main = do
  handles <- connectToExternalProcess
  sendCmd handles "do something"
  resp <- sendCmd "get results" -- needs strict I/O, before "quit"?
  sendCmd "quit"
  mapM_ putStrLn resp

I've tried using runInteractiveCommand, and several combinations of
hFlush, hWaitForInput, etc., but I can't find a combination that
actually works.

I know this is a sketchy description, but can anyone offer some sample
code, or point me toward a program that has similar behaviour?


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