It seems to be the case that SPECIALIZE pragmas are syntactically restricted to type specializations of a name (identifier) rather than a general expression. Is my understanding correct here? If so, is there any reason for this restriction?

I ask because I’m reifying Core code (into code that constructs a corresponding run-time representation for further processing), and I’m looking for a clean way to integrate that process with GHC, to support separate compilation and to avoid interfering with GHC’s regular flow. It occurred to me that I could enable separate compilation via a pragma of the form “{-# SPECIALIZE reify foo ∷ E t #-}” for some t, where E t is a reified form of values of type t. Type checking would infer the specialized type of foo, and the usual specialization phase would do its usual thing on that specialization, leaving “reify foo = reify specialized_foo”, and then the reification compiler plugin would transform the right-hand side, pushing the reify inward. Some reify calls may remain (e.g., due to polymorphism), triggering future rule applications. As much as possible of the fully-reified version would be factored out of the generated rule’s RHS for cheap reuse.

Thanks, - Conal