Yes, there are implementations for many of the type systems in the book. :) https://www.cis.upenn.edu/~bcpierce/tapl/checkers/ https://www.cis.upenn.edu/~bcpie

Yes, there are implementations for many of the type systems in the book. :) https://www.cis.upenn.edu/~bcpierce/tapl/checkers/ https://www.cis.upenn.edu/~bcpierce/tapl/checkers/ The code is pretty elegant. I think it's intended to be clear enough for students in his classes to modify.