#13018: TH-spliced pattern synonym declaration fails to typecheck -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Keywords: Resolution: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I made some progress in investigating the pattern synonyms codebase. This "partitioning" I wondered about in comment:7 is [http://git.haskell.org/ghc.git/blob/b4c3a66872a2b6e64fea9cc1f20ef4c8921ef7b6... described] in `Note [The pattern-synonym signature splitting rule]`: {{{ Note [The pattern-synonym signature splitting rule] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Given a pattern signature, we must split the kind-generalised variables, and the implicitly-bound variables into universal and existential. The rule is this (see discussion on Trac #11224): The universal tyvars are the ones mentioned in - univ_tvs: the user-specified (forall'd) universals - req_theta - res_ty The existential tyvars are all the rest }}} And in [http://git.haskell.org/ghc.git/blob/b4c3a66872a2b6e64fea9cc1f20ef4c8921ef7b6... tcCheckPatSynDecl], this is implemented [http://git.haskell.org/ghc.git/blob/b4c3a66872a2b6e64fea9cc1f20ef4c8921ef7b6... like so]: {{{#!hs let univ_fvs = closeOverKinds $ (tyCoVarsOfTypes (pat_ty : req_theta) `extendVarSetList` explicit_univ_tvs) (extra_univ, extra_ex) = partition ((`elemVarSet` univ_fvs) . binderVar) implicit_tvs univ_bndrs = extra_univ ++ mkTyVarBinders Specified explicit_univ_tvs ex_bndrs = extra_ex ++ mkTyVarBinders Specified explicit_ex_tvs univ_tvs = binderVars univ_bndrs ex_tvs = binderVars ex_bndrs }}} So I think in order to fix this bug, we'd just need to implement something analogous to the above in `repHsPatSynSigType`. But I'm stuck: the code above requires calculating free variables using `tyCoVarsOfTypes`, which takes `[Type]` as an argument. But in `repHsPatSynSigType`, we don't have `Type`s, we have `HsType`s! Is there an `HsType` counterpart to `tyCoVarsOfTypes` somewhere in the GHC codebase? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13018#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler