diff options
Diffstat (limited to 'compiler/GHC/Tc/Gen/App.hs')
| -rw-r--r-- | compiler/GHC/Tc/Gen/App.hs | 26 |
1 files changed, 20 insertions, 6 deletions
diff --git a/compiler/GHC/Tc/Gen/App.hs b/compiler/GHC/Tc/Gen/App.hs index 69a077c15b..4f04e82cf2 100644 --- a/compiler/GHC/Tc/Gen/App.hs +++ b/compiler/GHC/Tc/Gen/App.hs @@ -289,6 +289,7 @@ particular Ids: the renamer (Note [Handling overloaded and rebindable constructs] in GHC.Rename.Expr), and we want them to be instantiated impredicatively so that (f `op`), say, will work OK even if `f` is higher rank. + See Note [Left and right sections] in GHC.Rename.Expr. Note [Unify with expected type before typechecking arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -352,12 +353,26 @@ tcApp rn_expr exp_res_ty = addFunResCtxt rn_fun rn_args app_res_rho exp_res_ty $ thing_inside + -- Match up app_res_rho: the result type of rn_expr + -- with exp_res_ty: the expected result type + ; do_ds <- xoptM LangExt.DeepSubsumption ; res_wrap <- perhaps_add_res_ty_ctxt $ - tcSubTypeNC (exprCtOrigin rn_expr) GenSigCtxt (Just $ HsExprRnThing rn_expr) - app_res_rho exp_res_ty - -- Need tcSubType because of the possiblity of deep subsumption. - -- app_res_rho and exp_res_ty are both rho-types, so without - -- deep subsumption unifyExpectedType would be sufficient + if not do_ds + then -- No deep subsumption + -- app_res_rho and exp_res_ty are both rho-types, + -- so with simple subsumption we can just unify them + -- No need to zonk; the unifier does that + do { co <- unifyExpectedType rn_expr app_res_rho exp_res_ty + ; return (mkWpCastN co) } + + else -- Deep subsumption + -- Even though both app_res_rho and exp_res_ty are rho-types, + -- they may have nested polymorphism, so if deep subsumption + -- is on we must call tcSubType. + -- Zonk app_res_rho first, becuase QL may have instantiated some + -- delta variables to polytypes, and tcSubType doesn't expect that + do { app_res_rho <- zonkQuickLook do_ql app_res_rho + ; tcSubTypeDS rn_expr app_res_rho exp_res_ty } -- Typecheck the value arguments ; tc_args <- tcValArgs do_ql inst_args @@ -388,7 +403,6 @@ tcApp rn_expr exp_res_ty -------------------- wantQuickLook :: HsExpr GhcRn -> TcM Bool --- GHC switches on impredicativity all the time for ($) wantQuickLook (HsVar _ (L _ f)) | getUnique f `elem` quickLookKeys = return True wantQuickLook _ = xoptM LangExt.ImpredicativeTypes |