From: simonpj@microsoft.com <unknown>
Date: Tue, 3 Mar 2009 11:15:13 +0000 (+0000)
Subject: Comments only
X-Git-Tag: 2009-03-13~38
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=6d38e24ea3da7ca9b435e9b1e59b2de8fcd91da4

Comments only
---

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 0e1e5b0..4cf93e8 100644
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -710,6 +710,12 @@ tcSimplifyInfer doc tau_tvs wanted
 		-- irreds2 will be empty.  But we don't want to generalise over b!
 	; let preds2 = fdPredsOfInsts irreds2	-- irreds2 is zonked
 	      qtvs   = growInstsTyVars irreds2 tau_tvs2 `minusVarSet` oclose preds2 gbl_tvs2
+		---------------------------------------------------
+		-- BUG WARNING: there's a nasty bug lurking here
+		-- fdPredsOfInsts may return preds that mention variables quantified in
+		-- one of the implication constraints in irreds2; and that is clearly wrong:
+		-- we might quantify over too many variables through accidental capture
+		---------------------------------------------------
 	; let (free, irreds3) = partition (isFreeWhenInferring qtvs) irreds2
 	; extendLIEs free