From e9136762ee984451c45cd1067a41d7b7d5be0e19 Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Wed, 25 Nov 2015 16:27:45 +0000
Subject: Add a simplifier trace for eta-expansion

---
 compiler/simplCore/SimplUtils.hs | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/compiler/simplCore/SimplUtils.hs b/compiler/simplCore/SimplUtils.hs
index 1577efda37..4a5604196b 100644
--- a/compiler/simplCore/SimplUtils.hs
+++ b/compiler/simplCore/SimplUtils.hs
@@ -1302,7 +1302,10 @@ mkLam bndrs body cont
       , let body_arity = exprEtaExpandArity dflags body
       , body_arity > 0
       = do { tick (EtaExpansion (head bndrs))
-           ; return (mkLams bndrs (etaExpand body_arity body)) }
+           ; let res = mkLams bndrs (etaExpand body_arity body)
+           ; traceSmpl "eta expand" (vcat [text "before" <+> ppr (mkLams bndrs body)
+                                          , text "after" <+> ppr res])
+           ; return res }
 
       | otherwise
       = return (mkLams bndrs body)
-- 
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