In which language is the C# compiler written?

Question

I looked at the source code at http://referencesource.microsoft.com/, and it appears all the source code is in C#.

I also looked at the source code for the new C# co

Answer 1

The original C# compiler wasn't written in C#, it was in C and C++. The new Roslyn compiler was written in C#, but was initially compiled with the old compiler. Once the new compiler was done, it was able to compile its own source code: this is called bootstrapping.