The F# compiler, core library and core tools (open source edition)
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The Cross-Platform Packaging of the F# Compiler, Core Library & Tools

The main purpose of this repository is to package the open editions of the F# compiler, core library and core tools for use across multiple platforms.

Contributing to the F# Compiler, Core Library and Tools

Most contributions to the F# compiler/library/tools go first via the
repository at This ensures that the main packaging of F# on Windows (the Visual F# Tools) also includes any contributions that are made, and ensures that the versions do not diverge.

Contributing on Windows

If you are using Windows, you should fork the repo and contribute directly there. Your contributions will then be merged into this repo.

Contributing on Linux/OSX when using Mono

If you are using Linux or OSX, you can prepare your contributions by forking this repository (the code is essentially the same). This will give you access to the cross-platform testing available from this repo. At the moment the process is:

  1. Fork this repo.
  2. Build and test using the subset of tests available in this repo. If you like, submit a PR to this repo in order to trigger an automatic Travis run, or set up a Travis hook in your fork.
  3. Seek initial review by posting an issue in this repository or Make it clear you are working on Linux or OSX.
  4. Cherry-pick your changes into a pull request for and submit for final testing and clearance.
  5. The change will then be merged into this repo at a later point.

Contributions specifically related to cross-platform packaging should be made here.


The master branch is for F# 4.x. The fsharp4 branch archives F# 4.0, the fsharp31 branch archives F# 3.1.

To bootstrap the compiler, binaries built from an earlier version of this project are used.

This codebase uses the Apache 2.0 license.

Current Build Status

F# Branch OSX/Linux Windows
4.0+ master Build Status Build status
4.0 fsharp4 Build Status
3.1 fsharp31 Build Status
3.0 fsharp_30 Build Status

NuGet Feed of FSharp.Core and FSharp.Compiler.Tools packages

This repo is currently used to make two NuGet packages - FSharp.Core and FSharp.Compiler.Tools.

Stable builds are available in the NuGet Gallery: and

The FSharp.Core NuGet package includes all of the FSharp.Core redistributables from Visual F#. In addition, they include assemblies for MonoAndroid and MonoTouch built from this repository.

The FSharp.Compiler.Tools package includes the F# compiler fsc.exe, F# Interactive fsi.exe, build support, a copy of FSharp.Core used to run the tools, and related DLLs.

It can be used if you wish to use the latest F# compiler on a computer without relying on the installed version of Visual Studio. Adding it via nuget to a project will override the in-box compiler with the compiler from the nuget package. Note: due to how previous versions of the default project templates referenced Microsoft.FSharp.Targets, you may need to manually modify your project file once (see

A feed of nuget packages from builds is available from AppVeyor using the NuGet feed:

If using Paket, add the source at the top of paket.dependencies.


Add the dependency on FSharp.Core and run paket update. See the AppVeyor build history for a list of available versions. Here are some options for specifying the dependency:

nuget FSharp.Core
nuget FSharp.Core prerelease
nuget FSharp.Core
nuget FSharp.Core

If using NuGet Package Manager, add the source to the list of available package sources.

Available Package Sources

Build Requirements

Building F# on Unix-type platforms requires Mono 4.4 or higher. If you get a complaint in subsequent steps about xbuild being missing, it means you don't have Mono installed.

Building on OS X requires several development tools that are not installed by default. Most can be installed via Homebrew:

brew install autoconf automake pkg-config

Building on OS X also requires Xcode. If you don't want to install the full GUI development environment, the command line tools are sufficient. At a shell prompt, say:

xcode-select --install

How to Build

Linux and other Unix systems:

The usual:

./ --prefix=/usr
sudo make install

By default that makes optimized binaries. To make debug, use make CONFIG=debug


Use a prefix to your version of Mono:

./ --prefix=/Library/Frameworks/Mono.framework/Versions/Current/
sudo make install

By default that makes optimized binaries. To make debug, use make CONFIG=debug

Windows, using msbuild

Build using:


This build the proto compiler, then the library, then the final compiler.

You can also build these independently using:

msbuild src\fsharp-proto-build.proj
ngen install lib\proto\fsc-proto.exe
msbuild src\fsharp-library-build.proj /p:Configuration=Release
msbuild src\fsharp-compiler-build.proj /p:Configuration=Release

You can also build FSharp.Core.dll for other profiles:

msbuild src\fsharp-library-build.proj /p:TargetFramework=net20 /p:Configuration=Release
msbuild src\fsharp-library-build.proj /p:TargetFramework=portable47 /p:Configuration=Release
msbuild src\fsharp-library-build.proj /p:TargetFramework=portable7 /p:Configuration=Release
msbuild src\fsharp-library-build.proj /p:TargetFramework=portable78 /p:Configuration=Release
msbuild src\fsharp-library-build.proj /p:TargetFramework=portable259 /p:Configuration=Release

msbuild src\fsharp-library-build.proj /p:TargetFramework=monodroid /p:Configuration=Release
msbuild src\fsharp-library-build.proj /p:TargetFramework=monotouch /p:Configuration=Release

Change to /p:Configuration=Debug for debug binaries.

Windows, using xbuild (e.g. if only Mono is installed):

xbuild src\fsharp-proto-build.proj
xbuild src\fsharp-library-build.proj
xbuild src\fsharp-compiler-build.proj

Building using xbuild does not yet lay down a Mono-ready distribution (see src/fsharp/targets.make), so should only be used for private development rather than preparing distributions.

Build Note: Strong Names

The FSharp.Core.dll produced is only delay-signed (Mono does not require strong names). If a strong-name signed FSharp.Core.dll is needed then use the one in


How to Install

Built main compiler binaries go to Release/net40/bin

make install sends the binaries to the prefix location, e.g.


plus some files for xbuild support

/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/Microsoft\ F#/v4.0/*
/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/Microsoft\ SDKs/F#/3.0/Framework/*

(these names are the canonical names for Microsoft.FSharp.Targets used by project files coming from Visual Studio)

plus scripts

/usr/bin/fsharpc   (F# compiler)
/usr/bin/fsharpi   (F# Interactive)

Development Notes

Submitting Pull Requests

Feel free to send in-progress Pull Requests to ask for clarification or direction for a feature or task.

Integrating changes from 'visualfsharp'

To integrate latest changes from, use

git remote add visualfsharp
git pull visualfsharp master

There are certain guidelines that need to be followed when integrating changes from upstream:

  • this repository does not undergo the QA test process that upstream does, so the tests/fsharpqa folder and all files within should be removed when merging
  • this repository does not contain any of the Visual Studio tooling or integrations, so the vsintegration directory and all files within should be removed when merging
  • anything referencing FSharp.LaunguageService.Compiler is a Microsoft-internal version of the open FSharp.Compiler.Service repository, and as such should be removed when merging
  • Windows-specific update.cmd and runtests.cmd aren't used in this repository, and so should be removed when merging
  • anything that references the Salsa testing library is used by Microsoft to test the Visual Studio integrations, and as such should be removed when merging
  • the foremost example of the above is the root/unittests folder, which contains tests for the Visual Studio integration using Salsa, and as such should be removed when merging

Continuous Integration Build

A continuous integration build is set up with Travis. See above.

Editing the Compiler with Visual Studio, Xamarin Studio or MonoDevelop

Historically it is difficult to edit the compiler with Xamarin Studio or MonoDevelop because of bugs in loading the hand-edited project files and targets used in the F# compiler build. These are generally in the process of being fixed, your mileage will vary.

How to Test and Validate

Linux and OSX

Only a subset of the tests are currently enabled.

After building and installing, run

cd tests/fsharp/core


See the for instructions for how to test on Windows. Use that repository to develop and test on Windows.


F# compiler sources as initially dropped are available from

On 4 April 2014, Microsoft Open Tech published the F# compiler sources at and began accepting contributions to the F# compiler/library and tools.

In 2016 the Microsoft repo moved to GitHub at

This repository uses bootstrapping libraries, tools and F# compiler. The lib/bootstrap/X.0 directories contain mono-built libraries, compiler and tools that can be used to bootstrap a build. You can also supply your own via the --with-bootstrap option.

Wheezy build

vagrant up
vagrant ssh
cd /vagrant
sudo apt-get install dos2unix autoconf
./ --prefix=/usr
sudo make install


The maintainers of this repository appointed by the F# Core Engineering Group are: