The addition of functional dependencies to multi-parameter type classes all of a sudden opened up the possibility of doing type level computations that had not been there before. The type level programming industry seems to have started with Thomas Hallgren's 2001 paper Fun with Functional Dependencies (which got some inspiration from the type level numeric computation available in (classic) Bluespec ). Day 14: Deriving I don't know the history of deriving Functor et al. I believe Simon PJ added it after en
posted by augustss at 11:52 AM 2 comments
There's actually two way to get recursive do -notation. You can either use the rec keyword inside the do or you can use the keyword mdo instead of do . Why mdo , you ask? It should really be μdo , where μ is the recursion operator. But people at GHC HQ are scared of Unicode, so instead we got mdo . Day 9: Nullary Type Classes Once you have accepted multi-parameter type classes then nullary type classes are a natural consequence; zero is also a number, after all. In 1994 I worked on the pH language when I vi