I'm not sure how specific to Haskell this actually is, though. Think of templates in C++ (esp. template functions) or generics in Java. You use T or whatever as

I'm not sure how specific to Haskell this actually is, though. Think of templates in C++ (esp. template functions) or generics in Java. You use T or whatever as a placeholder for actual types. Any time you need more than one type, you're forced to make a similar decision about how to describe a type about which you know very little. It's is a heck of a lot more concise than either of those, though. Might this be the actual stumbling block? You're saying a lot about map -- in a very precise way, mind you -- without writing a lot.