[project @ 2002-10-30 09:29:33 by simonpj]

Fix an obscure record-selector-in-newtype bug

diff --git a/ghc/compiler/basicTypes/MkId.lhs b/ghc/compiler/basicTypes/MkId.lhs
index 1658786..1ad85bc 100644 (file)
--- a/ghc/compiler/basicTypes/MkId.lhs
+++ b/ghc/compiler/basicTypes/MkId.lhs
@@ -386,12 +386,12 @@ Then we want
 (not f :: R -> forall a. a->a, which gives the type inference mechanism 
 problems at call sites)
 
-Similarly for newtypes
+Similarly for (recursive) newtypes
 
        newtype N = MkN { unN :: forall a. a->a }
 
-       unN :: forall a. N -> a -> a
-       unN = /\a -> \n:N -> coerce (a->a) n
+       unN :: forall b. N -> b -> b
+       unN = /\b -> \n:N -> (coerce (forall a. a->a) n)
 
 \begin{code}
 mkRecordSelId tycon field_label
@@ -488,10 +488,10 @@ mkRecordSelId tycon field_label
              mkLams dict_ids $ mkLams field_dict_ids $
              Lam data_id     $ sel_body
 
-    sel_body | isNewTyCon tycon = mkNewTypeBody tycon field_tau (mk_result data_id)
+    sel_body | isNewTyCon tycon = mk_result (mkNewTypeBody tycon field_ty (Var data_id))
             | otherwise        = Case (Var data_id) data_id (default_alt ++ the_alts)
 
-    mk_result result_id = mkVarApps (mkVarApps (Var result_id) field_tyvars) field_dict_ids
+    mk_result poly_result = mkVarApps (mkVarApps poly_result field_tyvars) field_dict_ids
        -- We pull the field lambdas to the top, so we need to 
        -- apply them in the body.  For example:
        --      data T = MkT { foo :: forall a. a->a }
@@ -504,7 +504,7 @@ mkRecordSelId tycon field_label
                Nothing         -> Nothing
                Just the_arg_id -> Just (mkReboxingAlt uniqs data_con arg_ids body)
                                where
-                                  body = mk_result the_arg_id
+                                  body = mk_result (Var the_arg_id)
        where
             arg_ids = mkTemplateLocalsNum field_base (dataConOrigArgTys data_con)
                        -- No need to instantiate; same tyvars in datacon as tycon