You could argue compilers are good at making transformations to a program for optimization, but they are in many ways information starved. Cooperating with a compiler in the way http://www.yosefk.com/blog/humans-and-compilers-need-each-ot... describes, implies giving the compiler more information, external to the information that can be gathered from the source code. Type information should be helpful (tho disclaimer: I've never written a compiler), but it's information the compiler already has... That's not really cooperating with it. Just handing it stuff.