I like cabal-dev but it’s been giving me trouble for a while now. Using
sudo to install into the sandbox as root and failing to build any
combination of packages that share module names are the two most egregious
faults which have basically put me off using Haskell for a while now. After a
little research, I’ve managed to resolve both issues.
cabal-dev works by creating a Cabal configuration file for each sandbox and
passing it to the normal commands it uses to perform the various operations it
supports. Changing the configuration in this file does not have any effect as
it is regenerated every time cabal-dev is invoked. Instead I had to edit the
template file:
~/Library/Haskell/ghc-7.0.3/lib/cabal-dev-0.8/share/admin/cabal-config.in (I
use the Haskell Platform package for OS X, your location might vary).
“Global” installation in a sandbox
I’ve no idea why, but my cabal-config.in was configured to perform a
global installation by default. While global and user installations both put
their files in the same place, global installations used sudo to during the
installation process. Fixing this is a simple as changing the line:
user-install: FalseClashing module names
By far the most serious of the two problems was the clashing of module names
across packages. Amongst other things, I couldn’t install Snap because it
depends on two packages which contain modules called Control.Monad.CatchIO.
Again, the solution is a change to cabal-config.in. Both of the
install-dirs sections ought to look something like:
install-dirs user
prefix: ./
-- bindir: $prefix/bin
-- libdir: $prefix/lib
libsubdir: $pkgid/$compiler
-- libexecdir: $prefix/libexec
-- datadir: $prefix/share
datasubdir: $pkgid
docdir: $datadir/doc/$pkgid
-- htmldir: $docdir/html
-- haddockdir: $htmldirNote that the lines mentioning $pkgid have been uncommented. This will
result in cabal creating a per-package directory for the libraries, data,
documentation, etc. from each package. No more file name collisions!