Fix Trac #3406 (albeit not very satisfactorily): scoped type variables

[ghc-hetmet.git] / compiler / typecheck / TcSimplify.lhs

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 11e202b..e864b05 100644 (file)
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -45,7 +45,6 @@ import Class
 import FunDeps
 import PrelInfo
 import PrelNames
-import Type
 import TysWiredIn
 import ErrUtils
 import BasicTypes
@@ -54,7 +53,6 @@ import VarEnv
 import FiniteMap
 import Bag
 import Outputable
-import Maybes
 import ListSetOps
 import Util
 import SrcLoc
@@ -1589,13 +1587,23 @@ Simpler, maybe, but alas not simple (see Trac #2494)
 tcSimplifyRuleLhs :: [Inst] -> TcM ([Inst], TcDictBinds)
 tcSimplifyRuleLhs wanteds
   = do { wanteds' <- zonkInsts wanteds
-       ; (irreds, binds) <- go [] emptyBag wanteds'
+       
+               -- Simplify equalities  
+               -- It's important to do this: Trac #3346 for example
+        ; (_, wanteds'', tybinds, binds1) <- tcReduceEqs [] wanteds'
+        ; execTcTyVarBinds tybinds
+
+               -- Simplify other constraints
+       ; (irreds, binds2) <- go [] emptyBag wanteds''
+
+               -- Report anything that is left
        ; let (dicts, bad_irreds) = partition isDict irreds
        ; traceTc (text "tcSimplifyrulelhs" <+> pprInsts bad_irreds)
        ; addNoInstanceErrs (nub bad_irreds)
                -- The nub removes duplicates, which has
                -- not happened otherwise (see notes above)
-       ; return (dicts, binds) }
+
+       ; return (dicts, binds1 `unionBags` binds2) }
   where
     go :: [Inst] -> TcDictBinds -> [Inst] -> TcM ([Inst], TcDictBinds)
     go irreds binds []
@@ -3099,7 +3107,7 @@ groupErrs report_err (inst:insts)
    (friends, others) = partition is_friend insts
    loc_msg          = showSDoc (pprInstLoc (instLoc inst))
    is_friend friend  = showSDoc (pprInstLoc (instLoc friend)) == loc_msg
-   do_one insts = addInstCtxt (instLoc (head insts)) (report_err insts)
+   do_one insts = setInstCtxt (instLoc (head insts)) (report_err insts)
                -- Add location and context information derived from the Insts
 
 -- Add the "arising from..." part to a message about bunch of dicts
@@ -3308,7 +3316,7 @@ monomorphism_fix dflags
 warnDefault :: [(Inst, Class, Var)] -> Type -> TcM ()
 warnDefault ups default_ty = do
     warn_flag <- doptM Opt_WarnTypeDefaults
-    addInstCtxt (instLoc (head (dicts))) (warnTc warn_flag warn_msg)
+    setInstCtxt (instLoc (head (dicts))) (warnTc warn_flag warn_msg)
   where
     dicts = [d | (d,_,_) <- ups]