This is a pattern synonym to construct but more importantly to deconstruct an explicit `TypeRep a` into a `Typeable a` constraint

> asTypeable :: TypeRep a -> Dict (Typeable a)

> asTypeable rep =

> withTypeable rep

> Dict

> pattern Typeable :: () => Typeable a => TypeRep a

> pattern Typeable <- (asTypeable -> Dict)

> where Typeable = typeRep

Similar discussion for SingI [1], same benefits:

+ (Nice) direct alternative to CPS `withTypeable`

+ Reusable in other pattern synonyms