From: simonpj@microsoft.com <unknown>
Date: Wed, 6 Sep 2006 11:42:23 +0000 (+0000)
Subject: Comment on the commoning up of CoPats in Match
X-Git-Tag: After_FC_branch_merge~129
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=3cec5683766a13019c2835a4e79cc7e7dc066b96

Comment on the commoning up of CoPats in Match
---

diff --git a/compiler/deSugar/Match.lhs b/compiler/deSugar/Match.lhs
index 2d64633..d793343 100644
--- a/compiler/deSugar/Match.lhs
+++ b/compiler/deSugar/Match.lhs
@@ -745,6 +745,10 @@ sameGroup (PgN l1)   (PgN l2)   = True		-- Needs conditionals
 sameGroup (PgNpK l1) (PgNpK l2) = l1==l2	-- Order is significant
 						-- See Note [Order of n+k]
 sameGroup (PgCo	t1)  (PgCo t2)  = t1 `coreEqType` t2
+	-- CoPats are in the same goup only if the type of the
+	-- enclosed pattern is the same. The patterns outside the CoPat
+	-- always have the same type, so this boils down to saying that
+	-- the two coercions are identical.
 sameGroup _          _          = False
  
 patGroup :: Pat Id -> PatGroup