Frederik Eaton wrote:
I have a project which currently uses Cabal, and I would like to switch to using a plain Makefile.
I have two examples of projects that use Makefiles, darcs and jhc, but they both appear to hand-code the list of dependencies for executables. The "-M" option to ghc should let us do this automatically, but either because of a deficiency in GHC or in GNU Make, that looks to be impossible or difficult. Does anyone have experience with this?
Yes, GHC's build system works like this. We don't use --make at all when building GHC itself. However, I want to switch to using Cabal to build the libraries. Eventually I envisage using Cabal to build more parts of the GHC tree. There's certainly no reason that you can't use ghc -M with GNU make, and that's something we will continue to support. What problems are you having?
Since I'm not using the multi-compiler features of Cabal, I think it shouldn't be too hard to get the project-specific part of my Makefile down to the size of the .cabal file.
Sure, but you also have a quite a lot of build system infrastructure to get right. Incedentally, this is exactly what Cabal was meant to avoid.
- I want to be able to rebuild specific targets, rather than building everything every time
Multiple Cabal packages tied together with a simple Makefile could do this, no?
- I want better dependency inference, for instance I don't want to relink every executable every time I do a build (I think this is fixed in newer versions of ghc, but not the one I use)
Yes, fixed in 6.4.2 The comments about --make are interesting: ceratinly we're aware that it has a scalability problem, and it certainly isn't conducive to a frequent edit/compile/test cycle, which is one reason we don't use it in GHC. However, for a straight single-CPU build, from scratch, for a large program, and if you have a lot of memory, it is much faster than make. I don't have figures for GHC to hand, but I believe it is on the order of a factor of 2 or 3. I would expect 'make -j4' to definitely win on a 4-core box. We do have experimental patches for GHC to make --make work across multiple CPUs too, but you don't get linear speedup (single-threaded GC is one bottleneck). I think it would be prudent at some point to make Cabal build without --make and to add multiprocessor support. FWIW, I don't think 'ghc -c Foo.hs Bar.hs' goes any faster than separately compiling the two files, it doesn't cache anything between the two. Cheers, Simon