[Haskell-cafe] Type equality proof

[Martijn van Steenbergen]

Ryan Ingram wrote:
> These types are very useful for construction of type-safe interpreters
> and compilers.

That's exactly what I have in mind.

In my specific case I want to compare the constructors of the GADT 
representing a datatype family in the multirec package:

> data AST a where
>   Stmt :: AST Stmt
>   Expr :: AST Expr

Martijn.