#14288: ScopedTypeVariables with nested foralls broken since 8.0.2 -------------------------------------+------------------------------------- Reporter: MikolajKonarski | Owner: RyanGlScott Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler (Type | Version: 8.2.1 checker) | Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Yes, this is awkward. When we instantiate a type signature, we currently instantiate only the outer foralls and context. See `TcSigs.tcInstSig`. The scoped type variables come from the `sig_inst_skols`. Very similar story in `TcBinds.tcPolyCheck`. I suppose we can generalise this story. Instead of having {{{ data TcIdSigInst = TISI { ... , sig_inst_skols :: [(Name, TcTyVar)] , sig_inst_theta :: TcThetaType ... } }}} I suppose we could have a list of pairs of those things: {{{ data TcIdSigInst = TISI { ... , sig_inst_prefis :: [([(Name, TcTyVar)], TcThetaType)] ... } }}} Or maybe, more uniformly: {{{ data TcIdSigInst = TISI { ... , sig_inst_prefis :: [SigInstSpec] ... } data SigInstSpec = SITyVar Name TcTyVar | SIPred TcPredType }}} Then `tcInstType` might have type {{{ tcInstType :: (...) -> Id -> TcM ([SigInstSpec], TcRhoType) }}} I think we could carry this through uniformly. But I haven't tried. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14288#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler