tl;dr The F# language has been open source for 4 years and MS has accepted pull requests to the compiler, core library, and tools for over 6 months (100+ PRs g

tl;dr The F# language has been open source for 4 years and MS has accepted pull requests to the compiler, core library, and tools for over 6 months (100+ PRs going into F# v4.0). Now with Microsoft fully committed to open source and cross-OS development with .NET Core, this is a very good time for hackers interested in meta-programming to get in on the ground floor of F#, the only functional language fully supported by .NET. This article is a complete guide to hacking on the F# core, in this case an end to end example of extending the core library, including setting up standard unit tests. And mentions looking to F# Language Design User Voice, http://fslang.uservoice.com/ http://fslang.uservoice.com/ as the source for extension inspiration. One thing mentioned in the article, that F# will "likely" move from codeplex to Github, should read that the MS team is committed to fully migrate to Github, they are just busy right now with v4.0 of the language.