nix-shell --command "cabal configure"
cabal build
Applying parser combinators and free monads to a basic problem.
http://www.haskellforall.com/2012/06/you-could-have-invented-free-monads.html
http://www.haskellforall.com/2012/07/purify-code-using-free-monads.html
http://hackage.haskell.org/package/free-4.7.1/docs/Control-Monad-Free-TH.html