Sunday, June 22, 2014

Announcing ghc-make

Summary: I've released ghc-make, which is an alternative to ghc --make.

I've just released v0.2 of ghc-make (on Hackage, on Github). This package provides an alternative to ghc --make which supports parallel compilation of modules and runs faster when nothing needs compiling. To unpack that:

  • Parallel compilation: Call ghc-make -j4 and your program will build by running up to four ghc -c programs simultaneously. You usually need at parallel factor of 2x-3x to match ghc --make on a single core, since ghc --make does a lot of caching that is unavailable to ghc-make. If you use -j1, or omit a -j flag, the compilation will be based on ghc --make and should take the same time to compile.
  • Faster when nothing needs rebuilding: If ghc --make is slow when there is nothing to rebuild, and most of your executions do no rebuilding, ghc-make will make things go faster. On Windows I have one project where ghc --make takes 23 seconds and ghc-make takes 0.2 seconds (more than 100x faster). Particularly useful for scripts that do ghc --make Main && ./Main.

See the README for full details.

How do I use it?

Install ghc-make (cabal update && cabal install ghc-make). Then replace your calls to ghc my -arguments with ghc-make my -arguments. Almost all arguments and flags supported by ghc are supported by ghc-make - it is intended as a drop-in replacement. Let me know about any bugs on the bug tracker.

To use ghc-make with Cabal, try cabal build --with-ghc=ghc-make --ghc-options=-j4. (This technique is due to the ghc-parmake project, which also does parallel ghc --make compiles.)

How is it implemented?

This program uses the Shake library for dependency tracking and ghc --make for building. The actual ghc-make project itself only contains 4 modules, and the largest of those is the test suite.

To pass options to the underlying Shake build system prefix them with --shake, for example --shake--report=- will write a profile report to stdout and --shake--help will list the available Shake options.

2 comments:

Jan-Philip Loos said...

your bugtracker link starts with file:///S://
;)

Neil Mitchell said...

Jan-Philip: Thanks, now fixed - I managed to drop the http in an https:// somehow!