| Huh! It looks like what we currently do for some primops is just use a | totally bogus kind. For example, mkWeak# will happily accept an Int# as | its first argument. Well, I see primop MkWeakOp "mkWeak#" GenPrimOp o -> b -> (State# RealWorld -> (# State# RealWorld, c #)) and I believe (from Ben's message) that the "o" means "open type variable", which is the old terminology for what we now call levity-polymorphic. The type from primops.txt.pp is processed into various Haskell source files including compiler/stage1/build/primop-primop-info.hs-incl which includes primOpInfo MkWeakOp = mkGenPrimOp (fsLit "mkWeak#") [runtimeRep1TyVar, openAlphaTyVar, betaTyVar, gammaTyVar] [openAlphaTy, betaTy, (mkFunTy (mkStatePrimTy realWorldTy) ((mkTupleTy Unboxed [ mkStatePrimTy realWorldTy, gammaTy]))) , mkStatePrimTy realWorldTy] ((mkTupleTy Unboxed [mkStatePrimTy realWorldTy, mkWeakPrimTy betaTy])) So it looks as if (rightly or wrongly) mkWeak# is deliberately levity-polymorphic. It would be good to write this stuff down. A good starting point is https://ghc.haskell.org/trac/ghc/wiki/Commentary/PrimOps Simon So we *could* follow that precedent and generalize | reallyUnsafePtrEquality#, makeStableName#, etc., to accept anything, | whether it makes sense or not. Or we can work out how to do what I was | trying to do and then duplicate those primitives as appropriate | (mkLiftedWeak#, mkUnliftedWeak#, makeLiftedStableName#, | makeUnliftedStableName#, etc.).