Excerpts from John Dorsey's message of Wed Jul 30 13:58:26 -0500 2008:
Is something amiss with cabal-install? Shouldn't it have automatically installed alex? Or does it only do that with libraries, by design?
AFAICT, dependencies are only downloaded and installed if they are listed in a .cabal files 'dependency' field (providing they aren't already installed) which yes, means libraries by design. I've not had cabal-install ever track down necessary applications in my experience. As well, this issue came up on #haskell the other day and my conclusion is that no, cabal does not track down and install any *applications* that are necessary (someone tried to install yi, needed alex, build failed, and after 'cabal-install alex' everything was peachy.)
For that matter, "ghc-pkg list | grep -i alex" doesn't list anything, after I cabal-installed it. How does cabal verify the prerequisite alex version? (Or does it?)
ghc-pkg lists libraries that are registered with the ghc package manager (globally and locally); alex is simply an application, not a library, so there's really nothing for GHC to register. As for telling what version is necessary, I haven't the slightest. Duncan, can you shed some light here? Austin