ghc-make

The ghc-make program can be used as a drop-in replacement for ghc. This program targets two use cases: If a flag such as -j4 is passed, the modules will be compiled in parallel. If the available parallelism is greater than a factor of 3, the build will probably run faster. If there is no work to do (i.e. the compiled files are up-to-date), the build will run faster, sometimes significantly so. See the readme for full details: https://github.com/ndmitchell/ghc-make#readme.