When someone writes a new programming language, what do they write it IN?

Question

Please excuse my ignorance. I\'m dabbling in PHP and getting my feet wet browsing SO, and feel compelled to ask a question that I\'ve been wondering about for years:

Answer 1

Usually with a general-purpose programming language suitable for systems development, e.g. C, Haskell, ML, Lisp, etc., but the list of options is long. Also, usually with some domain-specific languages for language implementation, i.e. parser and lexical analyzer generators, intermediate languages like LLVM, etc. And probably some shell scripts, testing frameworks, and a build configuration system, e.g. autoconf.