Three improvements to Template Haskell (fixes #3467)

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

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 7aaa1ae..2ad5b2f 100644 (file)
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -17,8 +17,6 @@ module TcSimplify (
        tcSimplifyDeriv, tcSimplifyDefault,
        bindInstsOfLocalFuns, 
        
-        tcSimplifyStagedExpr,
-
         misMatchMsg
     ) where
 
@@ -45,7 +43,6 @@ import Class
 import FunDeps
 import PrelInfo
 import PrelNames
-import Type
 import TysWiredIn
 import ErrUtils
 import BasicTypes
@@ -54,7 +51,6 @@ import VarEnv
 import FiniteMap
 import Bag
 import Outputable
-import Maybes
 import ListSetOps
 import Util
 import SrcLoc
@@ -1589,13 +1585,23 @@ 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 []
@@ -1637,7 +1643,7 @@ this bracket again at its usage site.
 \begin{code}
 tcSimplifyBracket :: [Inst] -> TcM ()
 tcSimplifyBracket wanteds
-  = do { tryHardCheckLoop doc wanteds
+  = do { _ <- tryHardCheckLoop doc wanteds
        ; return () }
   where
     doc = text "tcSimplifyBracket"
@@ -2903,12 +2909,16 @@ disambigGroup :: [Type]                 -- The default types
              -> TcM () -- Just does unification, to fix the default types
 
 disambigGroup default_tys dicts
-  = try_default default_tys
+  = do { mb_chosen_ty <- try_default default_tys
+       ; case mb_chosen_ty of
+            Nothing        -> return ()
+            Just chosen_ty -> do { _ <- unifyType chosen_ty (mkTyVarTy tyvar) 
+                                ; warnDefault dicts chosen_ty } }
   where
     (_,_,tyvar) = ASSERT(not (null dicts)) head dicts  -- Should be non-empty
     classes = [c | (_,c,_) <- dicts]
 
-    try_default [] = return ()
+    try_default [] = return Nothing
     try_default (default_ty : default_tys)
       = tryTcLIE_ (try_default default_tys) $
        do { tcSimplifyDefault [mkClassPred clas [default_ty] | clas <- classes]
@@ -2918,10 +2928,7 @@ disambigGroup default_tys dicts
                -- For example, if Real a is reqd, but the only type in the
                -- default list is Int.
 
-               -- After this we can't fail
-          ; warnDefault dicts default_ty
-          ; unifyType default_ty (mkTyVarTy tyvar) 
-          ; return () -- TOMDO: do something with the coercion
+          ; return (Just default_ty) -- TOMDO: do something with the coercion
           }
 
 
@@ -3048,25 +3055,6 @@ tcSimplifyDefault theta = do
     doc = ptext (sLit "default declaration")
 \end{code}
 
-@tcSimplifyStagedExpr@ performs a simplification but does so at a new
-stage. This is used when typechecking annotations and splices.
-
-\begin{code}
-
-tcSimplifyStagedExpr :: ThStage -> TcM a -> TcM (a, TcDictBinds)
--- Type check an expression that runs at a top level stage as if
---   it were going to be spliced and then simplify it
-tcSimplifyStagedExpr stage tc_action
-  = setStage stage $ do { 
-        -- Typecheck the expression
-         (thing', lie) <- getLIE tc_action
-       
-       -- Solve the constraints
-       ; const_binds <- tcSimplifyTop lie
-       
-       ; return (thing', const_binds) }
-
-\end{code}
 
 
 %************************************************************************
@@ -3098,7 +3086,7 @@ 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
@@ -3307,7 +3295,7 @@ 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]