How to infer coercions?

coerce :: a -> b
coerce x = REDUCE (cast x) if a and b are incompatible
x                          otherwise

class Cast a, b where {cast :: a -> b };
-- ¬:: is an operator, literally meaning: don’t cast
--(!) is the reduction operator. Perform one stage of reduction.

-- Reduce on demand
instance Cast Exp c, c where { inline cast = ¬::(!)(x::(Exp c) -> ¬::(!)x) };