You were asking about getting the output of ':show modules' into a variable 'x', so that you can process it further. ':redir x :show modules' should do just that. There is another example command for implementing ':edit' this way (by now a native ghci command).
I think I'm seeing your meaning. So that brings me up to this:
let hlint _ = return $ unlines [":redir hlintvar1 :show modules", "let hlintvar2 = map (fst . break (==',') . drop 2 . snd . break (== '(')) $ lines hlintvar1", ":! hlint (concat $ intersperse \" \" hlintvar2"] :def hlint hlint
This doesn't work. The issue is that :! is weird; for it to work, one need to pass each argument as a separate string, and it won't evaluate a variable.
It isn't just ':!', quoting/variable interpretation is generally rather uncomfortable in GHCi scripting (so much so that I originally submitted output redirection as a patch before figuring out that it could be done without patching GHCi - that surprise find was the motivation for posting my findings as an email). Have you tried reading the mini tutorial that I keep mentioning and which the "using GHCi" page is pointing to? Here's the direct link: http://www.haskell.org/pipermail/haskell-cafe/2007-September/032260.html The discussion is rather brief, but that tutorial has several examples that need to work around issues like this, ranging from simple but tedious construct-the-command-string to extra levels of ':cmd' in order to get extra levels of interpretation (when you need to construct a command string from a variable that will be bound via a constructed command string (see the definitions of ':find', ':le' or ':b(rowse)' - the latter is an example of using the info from ':show modules'). Claus