add -fsimpleopt-before-flatten

[ghc-hetmet.git] / compiler / types / InstEnv.lhs

diff --git a/compiler/types/InstEnv.lhs b/compiler/types/InstEnv.lhs
index 49b49b8..07f68f7 100644 (file)
--- a/compiler/types/InstEnv.lhs
+++ b/compiler/types/InstEnv.lhs
@@ -45,7 +45,6 @@ import Data.Maybe     ( isJust, isNothing )
 %************************************************************************
 
 \begin{code}
-type DFunId = Id
 data Instance 
   = Instance { is_cls  :: Name         -- Class name
        
@@ -129,7 +128,7 @@ setInstanceDFunId ispec dfun
        -- are ok; hence the assert
      ispec { is_dfun = dfun, is_tvs = mkVarSet tvs, is_tys = tys }
    where 
-     (tvs, _, tys) = tcSplitDFunTy (idType dfun)
+     (tvs, _, _, tys) = tcSplitDFunTy (idType dfun)
 
 instanceRoughTcs :: Instance -> [Maybe Name]
 instanceRoughTcs = is_tcs
@@ -152,30 +151,40 @@ pprInstance ispec
 pprInstanceHdr :: Instance -> SDoc
 -- Prints the Instance as an instance declaration
 pprInstanceHdr ispec@(Instance { is_flag = flag })
-  = ptext (sLit "instance") <+> ppr flag
-    <+> sep [pprThetaArrow theta, ppr res_ty]
+  = getPprStyle $ \ sty ->
+    let theta_to_print
+          | debugStyle sty = theta
+          | otherwise = drop (dfunNSilent dfun) theta
+    in ptext (sLit "instance") <+> ppr flag
+       <+> sep [pprThetaArrow theta_to_print, ppr res_ty]
   where
-    (_, theta, res_ty) = tcSplitSigmaTy (idType (is_dfun ispec))
+    dfun = is_dfun ispec
+    (_, theta, res_ty) = tcSplitSigmaTy (idType dfun)
        -- Print without the for-all, which the programmer doesn't write
 
 pprInstances :: [Instance] -> SDoc
 pprInstances ispecs = vcat (map pprInstance ispecs)
 
 instanceHead :: Instance -> ([TyVar], ThetaType, Class, [Type])
-instanceHead ispec 
-   = (tvs, theta, cls, tys)
+-- Returns the *source* theta, without the silent arguments
+instanceHead ispec
+   = (tvs, drop n_silent theta, cls, tys)
    where
-     (tvs, theta, tau) = tcSplitSigmaTy (idType (is_dfun ispec))
-     (cls, tys) = tcSplitDFunHead tau
-
-mkLocalInstance :: DFunId -> OverlapFlag -> Instance
+     (tvs, theta, tau) = tcSplitSigmaTy (idType dfun)
+     (cls, tys)        = tcSplitDFunHead tau
+     dfun              = is_dfun ispec
+     n_silent          = dfunNSilent dfun
+
+mkLocalInstance :: DFunId
+                -> OverlapFlag
+                -> Instance
 -- Used for local instances, where we can safely pull on the DFunId
 mkLocalInstance dfun oflag
   = Instance { is_flag = oflag, is_dfun = dfun,
                is_tvs = mkVarSet tvs, is_tys = tys,
-               is_cls = className cls, is_tcs = roughMatchTcs tys }
+                is_cls = className cls, is_tcs = roughMatchTcs tys }
   where
-    (tvs, cls, tys) = tcSplitDFunTy (idType dfun)
+    (tvs, _, cls, tys) = tcSplitDFunTy (idType dfun)
 
 mkImportedInstance :: Name -> [Maybe Name]
                   -> DFunId -> OverlapFlag -> Instance
@@ -186,7 +195,7 @@ mkImportedInstance cls mb_tcs dfun oflag
                is_tvs = mkVarSet tvs, is_tys = tys,
                is_cls = cls, is_tcs = mb_tcs }
   where
-    (tvs, _, tys) = tcSplitDFunTy (idType dfun)
+    (tvs, _, _, tys) = tcSplitDFunTy (idType dfun)
 
 roughMatchTcs :: [Type] -> [Maybe Name]
 roughMatchTcs tys = map rough tys
@@ -354,6 +363,9 @@ data ClsInstEnv
                        --      If *not* then the common case of looking up
                        --      (C a b c) can fail immediately
 
+instance Outputable ClsInstEnv where
+  ppr (ClsIE is b) = ptext (sLit "ClsIE") <+> ppr b <+> pprInstances is
+
 -- INVARIANTS:
 --  * The is_tvs are distinct in each Instance
 --     of a ClsInstEnv (so we can safely unify them)
@@ -487,7 +499,7 @@ lookupInstEnv (pkg_ie, home_ie) cls tys
        find ((item, map (lookup_tv subst) dfun_tvs) : ms) us rest
 
        -- Does not match, so next check whether the things unify
-       -- See Note [overlapping instances] above
+       -- See Note [Overlapping instances] above
       | Incoherent <- oflag
       = find ms us rest
 
@@ -521,14 +533,18 @@ insert_overlapping new_item (item:items)
     old_beats_new = item `beats` new_item
 
     (instA, _) `beats` (instB, _)
-       = overlap_ok && 
-         isJust (tcMatchTys (is_tvs instB) (is_tys instB) (is_tys instA))
-               -- A beats B if A is more specific than B, and B admits overlap
-               -- I.e. if B can be instantiated to match A
-       where
-         overlap_ok = case is_flag instB of
-                       NoOverlap -> False
-                       _         -> True
+          = overlap_ok && 
+            isJust (tcMatchTys (is_tvs instB) (is_tys instB) (is_tys instA))
+                    -- A beats B if A is more specific than B,
+                    -- (ie. if B can be instantiated to match A)
+                    -- and overlap is permitted
+          where
+            -- Overlap permitted if *either* instance permits overlap
+            -- This is a change (Trac #3877, Dec 10). It used to
+            -- require that instB (the less specific one) permitted overlap.
+            overlap_ok = case (is_flag instA, is_flag instB) of
+                              (NoOverlap, NoOverlap) -> False
+                              _                      -> True
 \end{code}
 
 
@@ -540,8 +556,8 @@ insert_overlapping new_item (item:items)
 
 \begin{code}
 instanceBindFun :: TyVar -> BindFlag
-instanceBindFun tv | isTcTyVar tv && isExistentialTyVar tv = Skolem
-                  | otherwise                          = BindMe
+instanceBindFun tv | isTcTyVar tv && isOverlappableTyVar tv = Skolem
+                   | otherwise                              = BindMe
    -- Note [Binding when looking up instances]
 \end{code}
 
@@ -564,7 +580,7 @@ The op [x,x] means we need (Foo [a]).  Without the filterVarSet we'd
 complain, saying that the choice of instance depended on the instantiation
 of 'a'; but of course it isn't *going* to be instantiated.
 
-We do this only for pattern-bound skolems.  For example we reject
+We do this only for isOverlappableTyVar skolems.  For example we reject
        g :: forall a => [a] -> Int
        g x = op x
 on the grounds that the correct instance depends on the instantiation of 'a'