The best language to write a compiler in is the target language of the compiler. Citation please? Writing a compiler in the language it's targeting is not alwa

The best language to write a compiler in is the target language of the compiler. Citation please? Writing a compiler in the language it's targeting is not always "best", but it is often done to reduce dependence on external toolchains and to flush out bugs in the language or compiler itself (since a compiler is usually a fairly complex program). Every language has it's own benefits and drawbacks; the ML family of languages (which F# belongs to) was purpose-built for implementing compilers (and theorem-proving tools), so it would have been an excellent choice for implementing Roslyn, or at least parts of it.