From c776ac0002f484ab1fb087ae3d62efe581511f65 Mon Sep 17 00:00:00 2001
From: Steven Watanabe <steven@providere-consulting.com>
Date: Mon, 30 Aug 2010 02:26:02 +0000
Subject: [PATCH] Avoid evaluating BOOST_PP_SEQ_HEAD when it isn't needed. 
 Fixes #4465.

[SVN r65120]
---
 include/boost/preprocessor/seq/cat.hpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/boost/preprocessor/seq/cat.hpp b/include/boost/preprocessor/seq/cat.hpp
index 0efd8e5..b6b09ff 100644
--- a/include/boost/preprocessor/seq/cat.hpp
+++ b/include/boost/preprocessor/seq/cat.hpp
@@ -26,7 +26,7 @@
     BOOST_PP_IF( \
         BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(seq)), \
         BOOST_PP_SEQ_CAT_I, \
-        BOOST_PP_SEQ_HEAD(seq) BOOST_PP_TUPLE_EAT_1 \
+        BOOST_PP_SEQ_HEAD \
     )(seq) \
     /**/
 # define BOOST_PP_SEQ_CAT_I(seq) BOOST_PP_SEQ_FOLD_LEFT(BOOST_PP_SEQ_CAT_O, BOOST_PP_SEQ_HEAD(seq), BOOST_PP_SEQ_TAIL(seq))
@@ -39,10 +39,11 @@
 # define BOOST_PP_SEQ_CAT_S(s, seq) \
     BOOST_PP_IF( \
         BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(seq)), \
-        BOOST_PP_SEQ_CAT_S_I, \
-        BOOST_PP_SEQ_HEAD(seq) BOOST_PP_TUPLE_EAT_2 \
+        BOOST_PP_SEQ_CAT_S_I_A, \
+        BOOST_PP_SEQ_CAT_S_I_B \
     )(s, seq) \
     /**/
-# define BOOST_PP_SEQ_CAT_S_I(s, seq) BOOST_PP_SEQ_FOLD_LEFT_ ## s(BOOST_PP_SEQ_CAT_O, BOOST_PP_SEQ_HEAD(seq), BOOST_PP_SEQ_TAIL(seq))
+# define BOOST_PP_SEQ_CAT_S_I_A(s, seq) BOOST_PP_SEQ_FOLD_LEFT_ ## s(BOOST_PP_SEQ_CAT_O, BOOST_PP_SEQ_HEAD(seq), BOOST_PP_SEQ_TAIL(seq))
+# define BOOST_PP_SEQ_CAT_S_I_B(s, seq) BOOST_PP_SEQ_HEAD(seq)
 #
 # endif