Expression evaluation mode in haskell for scripting

Question

As noted multiple times elsewhere (eg. 1,2,...) scripting in haskell can be quite powerful.
A quick way can also be the ghc expression evaluation mode. this is what I actually find myself using more and more (I really like this feature in ruby).
A little example task:
"Find out all the folders that contained git diffs between the HEAD and a specific revision"

git diff --stat 9e2b68 | ghc -e \
  "getContents >>= return.(Data.List.nub).map(fst.break('/'==).head.words).lines"

This looks a little clunky, probably because I don't really know the details of using ghc -e.
Given that all the interesting part is just the nub.map(fst.break('/'==).head.words).lines the actual expression seems a little wordy.

• How do I tell ghc about modules I need to use so I don't need to qualify them using the full name?
• Can I make ghc pick up some kind of a configuration file that contains modules I frequently use?

I'd really appreciate seeing some examples from other usecases that will help my improve the way I use haskell for those kinds of little scripts!

Sidenote: Commandline-foo wizards will probably laugh at this but I feel much more comfortable using haskell then bash scripting so this is what I want to use.

Answer 1

Regarding modules: ghc -e uses your ~/.ghci file, so in this case, you'd add :m +Data.List to it (import Data.List(nub) is also supported since GHC 7 or so).

Regarding packages: You can use ghc-pkg hide somepackage and ghc-pkg expose somepackage to define the default set of visible packages (packages are exposed by default though; maybe I misunderstand your question).

You might find eddie useful.