#14255: Type-indexed type fingerprints -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: 8.2.1 Resolution: | Keywords: Typeable Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I assume that by "reduce the size of the trusted codebase", you mean eliminating uses of `unsafeCoerce`. But I don't see how indexing fingerprints with types would accomplish this. For example, fingerprints are used in `eqTypeRep`: {{{#!hs eqTypeRep :: forall k1 k2 (a :: k1) (b :: k2). TypeRep a -> TypeRep b -> Maybe (a :~~: b) eqTypeRep a b | typeRepFingerprint a == typeRepFingerprint b = Just (unsafeCoerce HRefl) | otherwise = Nothing }}} Are you envisioning changing this to the following? {{{#!hs eqTypeRep :: forall k1 k2 (a :: k1) (b :: k2). TypeRep a -> TypeRep b -> Maybe (a :~~: b) eqTypeRep a b = eq (typeRepFingerprint a) (typeRepFingerprint b) eq :: FingerPrintIx a -> FingerPrintIx b -> Maybe (a :~~: b) }}} If so, then that would axe one use of `unsafeCoerce`... but how are you planning to implement `eq`? I'm not sure how you would aside from using `unsafeCoerce` again! So we've traded one use of `unsafeCoerce` for another. Perhaps I'm way off base in my assumptions, so please correct me if you had a different vision in mind. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14255#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler