cabal usage

what is the recommended way (fewest keystrokes) for: * cabal install foo (download from hackage) * build failure => edit sources => repeat install on modified sources Is it really "cabal fetch foo" then "tar xvfz ~/.cabal/some/very/long/pathname.tgz" ? during the original "cabal install", sources seem to be in /tmp/TMPfoo-*/* but they are removed on failure. or - is this a workflow that should not happen (e.g. it might lead to confusing error messages later because "ghc-pkg list" shows the original version number if I forget to bump it while patching the sources) J.W.