The first edition of PLAI has a nice introductory chapter on types that explains this notation and has a whole section on type inference. It's also freely avail

The first edition of PLAI has a nice introductory chapter on types that explains this notation and has a whole section on type inference. It's also freely available online, so that's nice. (chapter 10 is on types) I haven't looked at the second edition at all yet, but the chapter on types looks like it has more code than math. Benjamin Pierce's Types and Programming Languages seems to be the gold standard of intro type theory, and definitely covers this notation and the math behind it, in a much more rigorous fashion than PLAI. It is a much deeper book though, so it doesn't get to type inference and Hindley Milner until later. I've read some of it and haven't actually gotten this far yet, but can say that it is a superb textbook, it's very well written and easy for an amateur to follow, as long as you're relatively comfortable reading and writing proofs. (but you don't need more math than your standard undergrad discrete math course) You might also want to look at Lambda the Ultimate's Getting Started page, which has a wide range of suggestions covering more than just types, but programming languages in general. http://lambda-the-ultimate.org/node/492 http://lambda-the-ultimate.org/node/492 http://www.cis.upenn.edu/~bcpierce/tapl/ http://www.cis.upenn.edu/~bcpierce/tapl/ http://cs.brown.edu/~sk/Publications/Books/ProgLangs/2007-04-26/ http://cs.brown.edu/~sk/Publications/Books/ProgLangs/2007-04...