From 264e667b86381528131c45c9b6e8f54ad168c73f Mon Sep 17 00:00:00 2001
From: Vance Shipley <vances@motivity.ca>
Date: Wed, 4 Apr 2012 18:17:33 +0530
Subject: extend re back reference syntax with \g escape sequence

Add the \gN and \g{N} syntax for back references in re:replace/3,4
to allow use with numeric replacement strings.
---
 lib/stdlib/doc/src/re.xml    | 4 ++--
 lib/stdlib/src/re.erl        | 6 ++++++
 lib/stdlib/test/re_SUITE.erl | 6 ++++++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/lib/stdlib/doc/src/re.xml b/lib/stdlib/doc/src/re.xml
index 6d5336796c..224b4b2771 100644
--- a/lib/stdlib/doc/src/re.xml
+++ b/lib/stdlib/doc/src/re.xml
@@ -524,8 +524,8 @@ This option makes it possible to include comments inside complicated patterns. N
 
       <p>The replacement string can contain the special character
       <c>&amp;</c>, which inserts the whole matching expression in the
-      result, and the special sequence <c>\</c>N (where N is an
-      integer &gt; 0), resulting in the subexpression number N will be
+      result, and the special sequence <c>\</c>N (where N is an integer &gt; 0),
+      <c>\g</c>N or <c>\g{</c>N<c>}</c> resulting in the subexpression number N will be
       inserted in the result. If no subexpression with that number is
       generated by the regular expression, nothing is inserted.</p>
       <p>To insert an <c>&amp;</c> or <c>\</c> in the result, precede it
diff --git a/lib/stdlib/src/re.erl b/lib/stdlib/src/re.erl
index 246d535943..70566e48dd 100644
--- a/lib/stdlib/src/re.erl
+++ b/lib/stdlib/src/re.erl
@@ -355,6 +355,12 @@ apply_mlist(Subject,Replacement,Mlist) ->
 
 precomp_repl(<<>>) ->
     [];
+precomp_repl(<<$\\,$g,${,Rest/binary>>) when byte_size(Rest) > 0 ->
+    {NS, <<$},NRest/binary>>} = pick_int(Rest),
+    [list_to_integer(NS) | precomp_repl(NRest)];
+precomp_repl(<<$\\,$g,Rest/binary>>) when byte_size(Rest) > 0 ->
+    {NS,NRest} = pick_int(Rest),
+    [list_to_integer(NS) | precomp_repl(NRest)];
 precomp_repl(<<$\\,X,Rest/binary>>) when X < $1 ; X > $9 ->
     %% Escaped character
     case precomp_repl(Rest) of
diff --git a/lib/stdlib/test/re_SUITE.erl b/lib/stdlib/test/re_SUITE.erl
index a542745e67..8ee0a13f4c 100644
--- a/lib/stdlib/test/re_SUITE.erl
+++ b/lib/stdlib/test/re_SUITE.erl
@@ -328,6 +328,12 @@ replace_return(Config) when is_list(Config) ->
     ?line <<"iXk">> = re:replace("abcdefghijk","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\9X",[{return,binary}]),
     ?line <<"jXk">> = re:replace("abcdefghijk","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\10X",[{return,binary}]),
     ?line <<"Xk">> = re:replace("abcdefghijk","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\11X",[{return,binary}]),
+    ?line <<"9X1">> = re:replace("12345678901","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\g9X",[{return,binary}]),
+    ?line <<"0X1">> = re:replace("12345678901","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\g10X",[{return,binary}]),
+    ?line <<"X1">> = re:replace("12345678901","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\g11X",[{return,binary}]),
+    ?line <<"971">> = re:replace("12345678901","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\g{9}7",[{return,binary}]),
+    ?line <<"071">> = re:replace("12345678901","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\g{10}7",[{return,binary}]),
+    ?line <<"71">> = re:replace("12345678901","(.)(.)(.)(.)(.)(.)(.)(.)(.)(.)","\\g{11}7",[{return,binary}]),
     ?line "a\x{400}bcX" = re:replace("a\x{400}bcd","d","X",[global,{return,list},unicode]),
     ?line <<"a",208,128,"bcX">> = re:replace("a\x{400}bcd","d","X",[global,{return,binary},unicode]),
     ?line "a\x{400}bcd" = re:replace("a\x{400}bcd","Z","X",[global,{return,list},unicode]),
-- 
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