diff --git a/src/builtins/Str.pir b/src/builtins/Str.pir
index 7ba0230..2493b41 100644
--- a/src/builtins/Str.pir
+++ b/src/builtins/Str.pir
@@ -1,4 +1,4 @@
-=head1 TITLE
+=head1 TITLE
 
 Str - Perl 6 Str class and related functions
 
@@ -155,11 +155,7 @@ Increment and Decrement Methods
   dec_2:
     dec ipos
     repl = substr RANGES, ipos, 1
-    $S0 = substr str, 0, r1
-    $I0 = r1 + 1
-    $S1 = substr str, $I0
-    str = concat $S0, repl
-    str = concat str, $S1
+    str  = replace str, r1, 1, repl
     # if the replacement wasn't a carry, we're done
     if orig > repl goto done
   carry:
@@ -190,11 +186,7 @@ Increment and Decrement Methods
     inc ipos
     .local string repl
     repl = substr RANGES, ipos, 1
-        $S0 = substr str, 0, r1
-    $I0 = r1 + 1
-    $S1 = substr str, $I0
-    str = concat $S0, repl
-    str = concat str, $S1
+    str  = replace str, r1, 1, repl
     # if the replacement wasn't a carry, we're done
     if orig < repl goto done
   carry:
@@ -206,11 +198,7 @@ Increment and Decrement Methods
     unless repl == '0' goto extend_1
     repl = '1'
   extend_1:
-    $S0 = substr str, 0, r0
-    $S1 = substr str, r0
-    str = concat $S0, repl
-    str = concat str, $S1
-
+    str = replace str, r0, 0, repl
   done:
     .return (str)
 .end
-- 

From 42acea630546f1641ae6914c459da53036b4e8c0 Mon Sep 17 00:00:00 2001
From: Jimmy Zhuo <zhuomingliang@yahoo.com.cn>
Date: Thu, 6 May 2010 15:51:19 +0800
Subject: use replace instead of substr

---
 src/builtins/Str.pir |   20 ++++----------------
 1 files changed, 4 insertions(+), 16 deletions(-)

diff --git a/src/builtins/Str.pir b/src/builtins/Str.pir
index 7ba0230..2493b41 100644
--- a/src/builtins/Str.pir
+++ b/src/builtins/Str.pir
@@ -1,4 +1,4 @@
-=head1 TITLE
+���=head1 TITLE
 
 Str - Perl 6 Str class and related functions
 
@@ -155,11 +155,7 @@ Increment and Decrement Methods
   dec_2:
     dec ipos
     repl = substr RANGES, ipos, 1
-    $S0 = substr str, 0, r1
-    $I0 = r1 + 1
-    $S1 = substr str, $I0
-    str = concat $S0, repl
-    str = concat str, $S1
+    str  = replace str, r1, 1, repl
     # if the replacement wasn't a carry, we're done
     if orig > repl goto done
   carry:
@@ -190,11 +186,7 @@ Increment and Decrement Methods
     inc ipos
     .local string repl
     repl = substr RANGES, ipos, 1
-        $S0 = substr str, 0, r1
-    $I0 = r1 + 1
-    $S1 = substr str, $I0
-    str = concat $S0, repl
-    str = concat str, $S1
+    str  = replace str, r1, 1, repl
     # if the replacement wasn't a carry, we're done
     if orig < repl goto done
   carry:
@@ -206,11 +198,7 @@ Increment and Decrement Methods
     unless repl == '0' goto extend_1
     repl = '1'
   extend_1:
-    $S0 = substr str, 0, r0
-    $S1 = substr str, r0
-    str = concat $S0, repl
-    str = concat str, $S1
-
+    str = replace str, r0, 0, repl
   done:
     .return (str)
 .end
-- 
1.6.4.msysgit.0