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GF Developers Guide


Before you start

This guide is intended for people who want to contribute to the development of the GF compiler or the Resource Grammar Library. If you are a GF user who just wants to download and install GF (e.g to develop your own grammars), the simpler guide on the GF download page should be sufficient.

Setting up your system for building GF

To build GF from source you need to install some tools on your system: the Haskell build tool Stack, the version control software Git and the Haskeline library.


The primary installation method is via Stack. (You can also use Cabal, but we recommend Stack to those who are new to Haskell.)

To install Stack:


To get the GF source code, you also need Git, a distributed version control system.


GF uses haskeline to enable command line editing in the GF shell.

Getting the source

Once you have all tools in place you can get the GF source code from GitHub:

Read-only access: clone the main repository

If you only want to compile and use GF, you can just clone the repositories as follows:

    $ git clone
    $ git clone

To get new updates, run the following anywhere in your local copy of the repository:

    $ git pull

Contribute your changes: fork the main repository

If you want the possibility to contribute your changes, you should create your own fork, do your changes there, and then send a pull request to the main repository.

  1. Creating and cloning a fork — See GitHub documentation for instructions how to create your own fork of the repository. Once you've done it, clone the fork to your local computer.

        $ git clone<YOUR_USERNAME>/gf-core.git

  2. Updating your copy — Once you have cloned your fork, you need to set up the main repository as a remote:

        $ git remote add upstream

    Then you can get the latest updates by running the following:

        $ git pull upstream master

  3. Recording local changes — See Git tutorial on how to record and push your changes to your fork.

  4. Pull request — When you want to contribute your changes to the main gf-core repository, create a pull request from your fork.

If you want to contribute to the RGL as well, do the same process for the RGL repository.

Compilation from source

By now you should have installed Stack and Haskeline, and cloned the Git repository on your own computer, in a directory called gf-core.

Primary recommendation: use Stack

Open a terminal, go to the top directory (gf-core), and type the following command.

  $ stack install

It will install GF and all necessary tools and libraries to do that.

Alternative: use Cabal

You can also install GF using Cabal, if you prefer Cabal to Stack. In that case, you may need to install some prerequisites yourself.

The actual installation process is similar to Stack: open a terminal, go to the top directory (gf-core), and type the following command.

  $ cabal install

The old (potentially outdated) instructions for Cabal are moved to a separate page. If you run into trouble with cabal install, you may want to take a look.

Compiling GF with C runtime system support

The C runtime system is a separate implementation of the PGF runtime services. It makes it possible to work with very large, ambiguous grammars, using probabilistic models to obtain probable parses. The C runtime system might also be easier to use than the Haskell runtime system on certain platforms, e.g. Android and iOS.

To install the C runtime system, go to the src/runtime/c directory.

Depending on what you want to do with the C runtime, you can follow one or more of the following steps.

Use the C runtime from another programming language

If you are on Mac and get an error about clang version, you can try some of these solutions—but be careful before removing any existing installations.

Use GF shell with C runtime support

If you get an "error while loading shared libraries" when trying to run GF with C runtime, remember to declare your LD_LIBRARY_PATH. Add export LD_LIBRARY_PATH="/usr/local/lib" to either your .bashrc or .profile. You should now be able to start GF with C runtime.

Use GF server mode with C runtime

Compilation of RGL

As of 2018-07-26, the RGL is distributed separately from the GF compiler and runtimes.

To get the source, follow the previous instructions on how to clone a repository with Git.

After cloning the RGL, you should have a directory named gf-rgl on your computer.


To install the RGL, you can use the following commands from within the gf-rgl repository:

  $ make install

There is also make build, make copy and make clean which do what you might expect.


For advanced build options, call the Haskell build script directly:

  $ runghc Setup.hs ...

For more details see the README.


If you do not have Haskell installed, you can use the simple build script (or Setup.bat for Windows).

Creating binary distribution packages

The binaries are generated with Github Actions. More details can be viewed here:

Running the test suite

The GF test suite is run with one of the following commands from the top directory:

    $ cabal test


    $ stack test

The testsuite architecture for GF is very simple but still very flexible. GF by itself is an interpreter and could execute commands in batch mode. This is everything that we need to organize a testsuite. The root of the testsuite is the testsuite/ directory. It contains subdirectories which themselves contain GF batch files (with extension .gfs). The above command searches the subdirectories of the testsuite/ directory for files with extension .gfs and when it finds one, it is executed with the GF interpreter. The output of the script is stored in file with extension .out and is compared with the content of the corresponding file with extension .gold, if there is one.

Every time when you make some changes to GF that have to be tested, instead of writing the commands by hand in the GF shell, add them to one .gfs file in the testsuite subdirectory where its .gf file resides and run the test. In this way you can use the same test later and we will be sure that we will not accidentally break your code later.

Test Outcome - Passed: If the contents of the files with the .out extension are identical to their correspondingly-named files with the extension .gold, the command will report that the tests passed successfully, e.g.

   Running 1 test suites...
   Test suite gf-tests: RUNNING...
   Test suite gf-tests: PASS
   1 of 1 test suites (1 of 1 test cases) passed.

Test Outcome - Failed: If there is a contents mismatch between the files with the .out extension and their corresponding files with the extension .gold, the test diagnostics will show a fail and the areas that failed. e.g.

    testsuite/compiler/compute/Records.gfs: OK
    testsuite/compiler/compute/Variants.gfs: FAIL
    testsuite/compiler/params/params.gfs: OK
    Test suite gf-tests: FAIL
    0 of 1 test suites (0 of 1 test cases) passed.

The fail results overview is available in gf-tests.html which shows 4 columns:

  1. Results - only areas that fail will appear. (Note: There are 3 failures in the gf-tests.html which are labelled as (expected). These failures should be ignored.)
  2. Input - which is the test written in the .gfs file
  3. Gold - the expected output from running the test set out in the .gfs file. This column refers to the contents from the .gold extension files.
  4. Output - This column refers to the contents from the .out extension files which are generated as test output. After fixing the areas which fail, rerun the test command. Repeat the entire process of fix-and-test until the test suite passes before submitting a pull request to include your changes.