[project @ 1998-12-22 16:31:28 by simonpj]

[ghc-hetmet.git] / ghc / compiler / main / MkIface.lhs

diff --git a/ghc/compiler/main/MkIface.lhs b/ghc/compiler/main/MkIface.lhs
index 065ae63..dbc8f08 100644 (file)
--- a/ghc/compiler/main/MkIface.lhs
+++ b/ghc/compiler/main/MkIface.lhs
@@ -53,7 +53,7 @@ import TyCon          ( TyCon, getSynTyConDefn, isSynTyCon, isNewTyCon, isAlgTyCon,
 import Class           ( Class, classBigSig )
 import SpecEnv         ( specEnvToList )
 import FieldLabel      ( fieldLabelName, fieldLabelType )
-import Type            ( mkSigmaTy, splitSigmaTy, mkDictTy, tidyTopType,
+import Type            ( mkSigmaTy, splitSigmaTy, mkDictTy, tidyTopType, deNoteType,
                          Type, ThetaType
                        )
 
@@ -227,7 +227,16 @@ ifaceInstances if_hdl inst_infos
     -------                     
     pp_inst (InstInfo clas tvs tys theta dfun_id _ _ _)
       = let                     
-           forall_ty     = mkSigmaTy tvs theta (mkDictTy clas tys)
+               -- The deNoteType is very important.   It removes all type
+               -- synonyms from the instance type in interface files.
+               -- That in turn makes sure that when reading in instance decls
+               -- from interface files that the 'gating' mechanism works properly.
+               -- Otherwise you could have
+               --      type Tibble = T Int
+               --      instance Foo Tibble where ...
+               -- and this instance decl wouldn't get imported into a module
+               -- that mentioned T but not Tibble.
+           forall_ty     = mkSigmaTy tvs theta (deNoteType (mkDictTy clas tys))
            renumbered_ty = tidyTopType forall_ty
        in                       
        hcat [ptext SLIT("instance "), pprType renumbered_ty,