type-equality primitive

[gelisam]

It is possible to write a macro which checks whether types like (-> Integer String) are equal, but for types like (-> (Maybe Integer) String), this is harder because the user can later introduce more datatypes which the macro doesn't know about.

I propose to provide a primitive macro which determines whether two types are known to be equal, or known to be apart. If the answer depends on what type unification variables will eventually resolve to, the macro is of course stuck until enough information is available.

[david-christiansen]

This seems like it's clearly useful. But rather than a macro, I'd make it an effect in the macro monad. That is, a type likeType -> Type -> Macro Bool rather than Syntax -> Macro Syntax, and not bound in a transformer environment.