Re: [Haskell-cafe] Associated data types

Lennart Augustsson wrote:

For an associated data type D, we know that the type function D is injective, i.e., for different indicies given to D we'll get different data types. This makes much more powerful reasoning possible in the type checker. If associated data types are removed there has to be some new mechanism to declare an associated type as injective, or the type system will lose power.

Interesting. Are you able to give an example which exploits this "known distinct types" effect?