Re: [Haskell-cafe] Cabal, lib and exe in one
On Tue, 2007-05-01 at 22:29 +0100, Magnus Therning 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 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.
Also, I don't really see what you mean by "that dir can be placed anywhere by the user". That dir is created as part of the build process and it's location is, AFAICS, always going to be ./dist/build.
Actually it's location can be set at configure time with --scratchdir= so that for example you could put it in a temp dir or something. Duncan
Duncan Coutts wrote:
On Tue, 2007-05-01 at 22:29 +0100, Magnus Therning 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 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
participants (2)
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Duncan Coutts -
Simon Marlow