Duncan Coutts wrote:
On Thu, 2007-05-03 at 16:49 +0200, Thomas Schilling wrote:
By dependencies I meant, library packages that GHC knows about.
For example, if I load something simple like
import System.Posix.Files main = touchFile "example" into GHCi and execute ":main" it prints
Loading package unix-1.0 ... linking ... done. Oh, right. Well, then please file it as a bug report on Cabal. I'll be working on Cabal configs as my Summer of Code project; this is clearly related. With a bit of luck it'll be done before end of August.
This is not a Cabal bug. By design, Cabal does not just pick up any packages from the environment like --make does. One of the main points of Cabal is to be able to explicitly track dependencies of a package, so we do require that they all be listed explicitly. Cabal then tells ghc to *only* look in those listed packages and ignore all others even if they happen to be installed.
Now certainly it would be nicer if ghc+cabal could be more helpful and tell you all the missing packages that you need to list in the "build-depends" field in the .cabal file, rather than currently where you have to do it one by one.
This feature could be implemented in GHC, or it could actually be implemented in Cabal. To do it in cabal requires that cabal gain an infrastructure for doing dependency analysis of modules. We don't have that yet. We do need this infrastructure anyway though, since for example some pre-processors (notably c2hs) need to be called in dependency order. It would also allow other nice things like having cabal work out for you exactly which pre-processors and build tools are required, and make partial and parallel rebuilds possible.
ghc --show-iface Main.hi | grep 'package dependencies'
This doesn't do exactly what you want, but it's useful nonetheless: package dependencies: base haskell98 Cheers, Simon