It took about one year. We originally implemented the compiler in Ruby and because of its similarity with Crystal (or the other way around ;-)) porting it to Crystal was pretty easy in the end.

There's this tag: https://github.com/manastech/crystal/releases/tag/ruby

You can read about the bootstrapping moment here: http://crystal-lang.org/2013/11/14/good-bye-ruby-thursday.ht...