Cabal (and cabal-install) 1.18.0 is out and so are some fantastic improvements to make Haskell even more awesome.
To get it, just update:
$ cabal update $ cabal install Cabal-1.18.0 cabal-install-1.18.0
Here's how working on a package might look like using the new features:
# Only once: $ cabal sandbox init $ cabal install --only-dependencies --enable-tests # Play around with the code in GHCi: $ cabal repl
More about the user visible changes: