Commit e0b93c02 authored by chak@cse.unsw.edu.au.'s avatar chak@cse.unsw.edu.au.
Browse files

Fix for 1st half of #2203

parent af97da87
......@@ -1486,22 +1486,26 @@ checkValidInstHead ty -- Should be a source type
check_inst_head :: DynFlags -> Class -> [Type] -> TcM ()
check_inst_head dflags clas tys
-- If GlasgowExts then check at least one isn't a type variable
= do checkTc (dopt Opt_TypeSynonymInstances dflags ||
= do { -- If GlasgowExts then check at least one isn't a type variable
; checkTc (dopt Opt_TypeSynonymInstances dflags ||
all tcInstHeadTyNotSynonym tys)
(instTypeErr (pprClassPred clas tys) head_type_synonym_msg)
checkTc (dopt Opt_FlexibleInstances dflags ||
; checkTc (dopt Opt_FlexibleInstances dflags ||
all tcInstHeadTyAppAllTyVars tys)
(instTypeErr (pprClassPred clas tys) head_type_args_tyvars_msg)
checkTc (dopt Opt_MultiParamTypeClasses dflags ||
; checkTc (dopt Opt_MultiParamTypeClasses dflags ||
isSingleton tys)
(instTypeErr (pprClassPred clas tys) head_one_type_msg)
mapM_ check_mono_type tys
-- May not contain type family applications
; mapM_ checkTyFamFreeness tys
; mapM_ check_mono_type tys
-- For now, I only allow tau-types (not polytypes) in
-- the head of an instance decl.
-- E.g. instance C (forall a. a->a) is rejected
-- One could imagine generalising that, but I'm not sure
-- what all the consequences might be
}
where
head_type_synonym_msg = parens (
......@@ -1719,7 +1723,7 @@ checkFamInst lhsTys famInsts
checkTyFamFreeness :: Type -> TcM ()
checkTyFamFreeness ty
= checkTc (isTyFamFree ty) $
tyFamInstInIndexErr ty
tyFamInstIllegalErr ty
-- Check that a type does not contain any type family applications.
--
......@@ -1728,9 +1732,9 @@ isTyFamFree = null . tyFamInsts
-- Error messages
tyFamInstInIndexErr :: Type -> SDoc
tyFamInstInIndexErr ty
= hang (ptext (sLit "Illegal type family application in type instance") <>
tyFamInstIllegalErr :: Type -> SDoc
tyFamInstIllegalErr ty
= hang (ptext (sLit "Illegal type synonym family application in instance") <>
colon) 4 $
ppr ty
......
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