#13848: Unexpected order of variable quantification with GADT constructor -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Keywords: Resolution: | TypeApplications 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): The question remains: how could we preserve the order in which the user wrote the `forall`d variables? The assumption that they should be partitioned into separate universal and existential groups is baked pretty deeply into the GHC AST, as `DataCon` has separate `dcUnivTyVars` and `dcExTyVars` fields, and never the twain shall meet. One possible solution is to introduce a `dcOrigTyVars :: Maybe [TyVar]` field, which is `Just` the `forall`d variables (in whatever order the user writes) or `Nothing` otherwise. GHC could then use this information when computing `dataConUserType`, which I believe GHC uses for determining the order in which `TypeApplications` happen. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13848#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler