I'm not sure about specifically. A joyful synergy, maybe. The fact that compilers are, in essence, pure functions, maps from input programs to output programs, was recognized quite early on. I can't put my finger on the origin of the idea, but it may have been understood by Turing himself. Well-understood in the Lisp world by the late 1960s, before ML came along. Parsers and compiler data structures, translate extremely well into recursive functions, operating on algebraic data types. These are applicable to many other problems, but compilers have always had centre place in the functional showroom. Sometimes I do wonder if it's just navel-gazing, though -- look, functional languages are useful for implementing functional languages!