I think Simon is right, and not just from a Haskell point of view. Allowing a package to contain a both a library and an executable makes the behavior of the package system less obvious. That's not to say that it can't behave "correctly", but that it can't behave both "correctly" and in a way that is easy to understand. Yes, it makes installation of an executable package more complicated if you have to install its library package as well. But making this simple should be handled by a layer above the cabal package files (Hackage?). In my experience, the best packaging systems distinguish between dependency assurance and dependency satisfaction. For example, the Debian packaging system has two layers. dpkg deals with package files, installing a single package, and assuring that dependencies are met prior to installation. apt-get retrieves packages from repositories with their pre-reqs (based on the dependency) and invokes dpkg on the retrieved packages. I know the problem is not identical to the one cabal is trying to solve, but I think there is a great deal to be learned by looking at the Debian packaging system and its conventions. In any event, solid naming conventions could go a long way to making this obvious. If foo has a useful exposed library, but primarily consists of an executable, dividing it into foo-bin and foo-lib could serve to clarify. I would propose that, since the bulk of existing packages seem to be libraries, we use a naming convention to distinguish packages that build executables and leave the names of library packages unannotated. -r On May 2, 2007, at 2:08 AM, Simon Marlow wrote:
Duncan Coutts wrote:
So if foo.hs is in test-src and Foo/Bar.hs is in src then I think you just need:
hs-source-dirs: test-src, src No, that's not enough, I also have to add the following lines to make the executable compile and link:
extensions: ForeignFunctionInterface c-sources: csrc/ptrace.c
That is, I end up compiling the library a second time! Can't I get the executable to link against the library that was just created? I was just expecting to not have to repeat myself in the cabal file. Not such a strange thing to expect from a build system, I think :-) Yes this is an interesting question about what it means to have
On Tue, 2007-05-01 at 22:29 +0100, Magnus Therning wrote: programs in the same cabal package as an executable. Currently having a executable and a library inside a cabal package is not the same thing as having a library package and separate package that contains only that executable. The difference is that when the executable is in the same cabal package it merely has access to the same modules, it doesn't 'depend' on that library package exactly. So for example it can access modules which are not exposed by the library and indeed it can compile those same modules with completely different build flags. So currently those modules will be built twice. It's not clear to me that this is the right meaning, or indeed that we should allow multiple entries in a single .cabal file. I think it might be better to just have multiple .cabal files (possibly in the same directory). Then we could be explicit and state that an executable depends on the library or if we want to use different build flags, or use modules that are not exposed by the lib then we can do that and only in that case do we build those modules twice.
Right at the front of the Cabal docs it says:
"However having both a library and executables in a package does not work very well; if the executables depend on the library, they must explicitly list all the modules they directly or indirectly import from that library."
IMO we shouldn't allow both a library and an exe in the same package. I think I argued against this originally, and my understanding is that doing this is deprecated, although perhaps not visibly enough. Whenever the question of what to do about lib +exe packages arises, the discussion tends to spiral out of control into what we should do about collections of packages in general.
For now, the simple story is that each package should have either a single library or a single executable (even multiple executables in a package is questionable; if they share some code it shoud be in a package).
Cheers, Simon _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe