For Windows users, all the commands below must be executed in the MinGW shell, not Command Prompt or PowerShell.
Then, get the sources by cloning GHC's main Git repository or via an alternative method (see Getting the Sources for more details). Note: you can connect to GitLab using SSH, if you register to GitLab and upload your SSH key. In that case the following line would have "git:" instead of "https:"
Optionally, you can customize your build by creating the file mk/build.mk using mk/build.mk.sample as a template and e.g. removing the comment marker # on the line "BuildFlavour = devel2".
If you obtained the repository via git clone --recursive, you will need to first run:
This step isn't necessary if you obtained the source from a tar archive.
Next, run the ./configure script followed by make to start the build:
$ ./configure # Windows users must append "--enable-tarballs-autodownload"$ make -j8 # Use 8 parallel jobs; adapt to actual number of cpu cores
On Windows you need to download some binary distributables before being able to build. This only has to be done once and can be done by adding the --enable-tarballs-autodownload flag to the call to ./configure.
By default (without any mk/build.mk customization), this will do a 2-stage bootstrap build of the compiler, with profiling libraries.
Run without installing
You can find the binaries built by make in the inplace/bin directory under the root of the ghc source tree. The binaries can be run from here without installing.
After building, to install GHC (by default in /usr/local):
Don't run make directly in the ghc root directory (unless you just pulled in changes from others). Instead, first
change to the directory (compiler, utils, ghc or libraries) where you're making your changes.
See Building a single sub-component.
While in the sub-component directory, use make fastskip dependency building (except after pulling in changes from others).
A good first sanity check is to twiddle some error message in the code, just to see that changed error message pop up when you compile a file. Write some Haskell code with an error in it, and look at the error message. Search through the code for that error message. Change the message, rebuild ghc (run make fast in the ghc directory), and recompile your file again with ./inplace/bin/ghc-stage2. If you see the changed message, you're good to go.
Check out a Stable Release
You can learn what branches are available via git branch -a. You can e.g. switch to the latest stable release of GHC-8.6.x:
git checkout ghc-8.6
You'll then have to update the git submodules:
git submodule update --init
Has your question not been answered? See Building for more resources. Also, don't hestitate to ask for help.