compilers are really complicated pieces of software. There's a lot of complexity even in small routines. I would expect to encounter complicated types in there,

compilers are really complicated pieces of software. There's a lot of complexity even in small routines. I would expect to encounter complicated types in there, they capture (while complex) intent and meaning. It's not the frontend glue-code kind of code. The inherently hard problem makes is fun for people who like to solve small puzzles.