#12670: Representation polymorphism validity check is too strict -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.0.1 checker) | 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 bgamari): The patch that Simon was referring to in comment:4 was eefe86d96d40697707c3ddfb9973a30a1897241f. Unfortunately this doesn't fix the issue which described by this ticket; the typechecker still rejects the program given in the ticket description. Richard and I discussed this a few weeks ago and came to a solution which looks something like this, {{{#!patch diff --git a/compiler/typecheck/TcPatSyn.hs b/compiler/typecheck/TcPatSyn.hs index 5c62121..62724c8 100644 --- a/compiler/typecheck/TcPatSyn.hs +++ b/compiler/typecheck/TcPatSyn.hs @@ -13,6 +13,7 @@ module TcPatSyn ( tcInferPatSynDecl, tcCheckPatSynDecl ) where import HsSyn +import TcHsSyn( checkForRepresentationPolymorphism ) import TcPat import Type( mkTyVarBinders, mkEmptyTCvSubst , tidyTyVarBinders, tidyTypes, tidyType ) @@ -312,6 +313,9 @@ tc_patsyn_finish lname dir is_infix lpat' arg_tys = tidyTypes env2 arg_tys' pat_ty = tidyType env2 pat_ty' + -- Check that the arguments aren't representationally polymorphic + ; mapM_ (checkForRepresentationPolymorphism empty) arg_tys + ; traceTc "tc_patsyn_finish {" $ ppr (unLoc lname) $$ ppr (unLoc lpat') $$ ppr (univ_tvs, req_theta, req_ev_binds, req_dicts) $$ diff --git a/compiler/typecheck/TcTyClsDecls.hs b/compiler/typecheck/TcTyClsDecls.hs index c009bc9..9335676 100644 --- a/compiler/typecheck/TcTyClsDecls.hs +++ b/compiler/typecheck/TcTyClsDecls.hs @@ -2296,6 +2296,9 @@ checkValidDataCon dflags existential_ok tc con -- Check all argument types for validity ; checkValidType ctxt (dataConUserType con) + -- Check for representationally polymorphic fields + ; mapM_ (checkForRepresentationPolymorphism empty) (dataConOrigArgTys con) + -- Extra checks for newtype data constructors ; when (isNewTyCon tc) (checkNewDataCon con) diff --git a/compiler/typecheck/TcValidity.hs b/compiler/typecheck/TcValidity.hs index 6cc40a5..c9f3bda 100644 --- a/compiler/typecheck/TcValidity.hs +++ b/compiler/typecheck/TcValidity.hs @@ -487,8 +487,6 @@ check_type _ _ _ (TyVarTy _) = return () check_type env ctxt rank (FunTy arg_ty res_ty) = do { check_type env ctxt arg_rank arg_ty - ; when (representationPolymorphismForbidden ctxt) $ - checkForRepresentationPolymorphism empty arg_ty ; check_type env ctxt res_rank res_ty } where (arg_rank, res_rank) = funArgResRank rank }}} Unfortunately this still doesn't fix the Core Lint issues that inevitably pop up when you try to use such a type. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12670#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler