X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FbasicTypes%2FVarEnv.lhs;h=f3a093aed8fb2f9573945e78d8f001b1c3611021;hp=3c9f53ae04a9c7f29a8fa9bfe9e125c8f8f5037f;hb=6a05ec5ef5373f61b7f9f5bdc344483417fa801b;hpb=49c98d143c382a1341e1046f5ca00819a25691ba

diff --git a/compiler/basicTypes/VarEnv.lhs b/compiler/basicTypes/VarEnv.lhs
index 3c9f53a..f3a093a 100644
--- a/compiler/basicTypes/VarEnv.lhs
+++ b/compiler/basicTypes/VarEnv.lhs
@@ -4,6 +4,13 @@
 %
 
 \begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
 module VarEnv (
 	VarEnv, IdEnv, TyVarEnv,
 	emptyVarEnv, unitVarEnv, mkVarEnv,
@@ -28,7 +35,7 @@ module VarEnv (
 	-- RnEnv2 and its operations
 	RnEnv2, mkRnEnv2, rnBndr2, rnBndrs2, rnOccL, rnOccR, inRnEnvL, inRnEnvR,
 		rnBndrL, rnBndrR, nukeRnEnvL, nukeRnEnvR, extendRnInScopeList,
-		rnInScope, lookupRnInScope,
+		rnInScope, rnInScopeSet, lookupRnInScope,
 
 	-- TidyEnvs
 	TidyEnv, emptyTidyEnv
@@ -196,6 +203,9 @@ extendRnInScopeList env vs
 rnInScope :: Var -> RnEnv2 -> Bool
 rnInScope x env = x `elemInScopeSet` in_scope env
 
+rnInScopeSet :: RnEnv2 -> InScopeSet
+rnInScopeSet = in_scope
+
 rnBndrs2 :: RnEnv2 -> [Var] -> [Var] -> RnEnv2
 -- Arg lists must be of equal length
 rnBndrs2 env bsL bsR = foldl2 rnBndr2 env bsL bsR 
@@ -226,21 +236,33 @@ rnBndr2 (RV2 { envL = envL, envR = envR, in_scope = in_scope }) bL bR
 rnBndrL, rnBndrR :: RnEnv2 -> Var -> (RnEnv2, Var)
 -- Used when there's a binder on one side or the other only
 -- Useful when eta-expanding
+-- 
 rnBndrL (RV2 { envL = envL, envR = envR, in_scope = in_scope }) bL
   = (RV2 { envL     = extendVarEnv envL bL new_b
-	 , envR     = envR
+	 , envR     = extendVarEnv envR new_b new_b 	-- Note [rnBndrLR]
 	 , in_scope = extendInScopeSet in_scope new_b }, new_b)
   where
-    new_b | not (bL `elemInScopeSet` in_scope) = bL
-      	  | otherwise			       = uniqAway' in_scope bL
+    new_b = uniqAway in_scope bL
 
 rnBndrR (RV2 { envL = envL, envR = envR, in_scope = in_scope }) bR
-  = (RV2 { envL     = envL
+  = (RV2 { envL     = extendVarEnv envL new_b new_b	-- Note [rnBndrLR]
 	 , envR     = extendVarEnv envR bR new_b
 	 , in_scope = extendInScopeSet in_scope new_b }, new_b)
   where
-    new_b | not (bR `elemInScopeSet` in_scope) = bR
-      	  | otherwise			       = uniqAway' in_scope bR
+    new_b = uniqAway in_scope bR
+
+-- Note [rnBndrLR] 
+-- ~~~~~~~~~~~~~~~
+-- Notice that in rnBndrL, rnBndrR, we extend envR, envL respectively
+-- with a binding [new_b -> new_b], where new_b is the new binder.
+-- This is important when doing eta expansion; e.g. matching (\x.M) ~ N
+-- In effect we switch to (\x'.M) ~ (\x'.N x'), where x' is new_b
+-- So we must add x' to the env of both L and R.  (x' is fresh, so it
+-- can't capture anything in N.)  
+--
+-- If we don't do this, we can get silly matches like
+--	forall a.  \y.a  ~   v
+-- succeeding with [x -> v y], which is bogus of course 
 
 rnOccL, rnOccR :: RnEnv2 -> Var -> Var
 -- Look up the renaming of an occurrence in the left or right term