left zero pad digit string

Padding a number:
Requirement: zero pad a digit string 
Example: 456 --> 000456
Where the new string length is a passed parameter to the padding template.
 
I am attempting to left zero pad a number.  Presently unable to get more
than 1 digit padding with my recursive padding template (below).
I desire the effect of chaining concat calls.
Code attached below. 
 
Alternatives:
1. format-number() does not appear to be an option for two reasons: 1)
unable to specify the formatting with element or attribute values; 2) do not
believe it will left pad zeroes.
 
2. brute force, not in the xsl spirit.
  <xsl:template name="format-batchnum">
    <xsl:param name="batchnum" select="0"/>
    <xsl:param name="numbatchdigit" select="1"/>
 
      <!-- zero string - 64 zeroes -->
    <xsl:variable name="zerostr"
select="string('000000000000000000000000000000000000000000000000000000000000
0000')"/>
    <xsl:variable name="padsize" select="$numbatchdigit -
string-length($batchnum)"/>
    <xsl:variable name="zeropad" select="substring($zerostr, 1, $padsize)"/>
    <xsl:value-of select="concat($zeropad, $batchnum)"/>
  </xsl:element>
 
 
Thanks for any suggestions.
Joel
 
 Attached code:
 
    <!-- in calling template -->
    <!-- example data: nextstartbatchnum = 4020, numbatchdigit = 12 -->
    <!-- desired result: 000000004020 (12 digits in total) -->
  <xsl:call-template name="format-batchnum">
     <xsl:with-param name="batchnum" select="nextstartbatchnum"/>
     <xsl:with-param name="numbatchdigit" select="numbatchdigit"/>
  </xsl:call-template>
  
 
    <!-- left zero pad batchnumber to numbatchdigit size -->
<xsl:template name="format-batchnum">
   <xsl:param name="batchnum" select="0"/>
   <xsl:param name="numbatchdigit" select="1"/>
 
   <xsl:variable name="padded-number">
     <xsl:call-template name="pad-number">
       <xsl:with-param name="number" select="$batchnum"/>
       <xsl:with-param name="pad" select="$numbatchdigit -
string-length($batchnum)"/>
     </xsl:call-template>
   </xsl:variable>
   <xsl:value-of select="$padded-number"/>
</xsl:template>
 
    <!-- recursive padding template -->
    <!-- each call concat leading zero -->
    <!-- basecase: pad = 0 -->
<xsl:template name="pad-number">
   <xsl:param name="number" select="0"/>
   <xsl:param name="pad" select="0"/>
 
   <xsl:choose>
     <xsl:when test="pad &gt; 0">
       <xsl:variable name="number">
         <xsl:call-template name="pad-number">
           <xsl:with-param name="number" select="$number"/>
           <xsl:with-param name="pad" select="$pad -1"/>
         </xsl:call-template>
       </xsl:variable>
     </xsl:when>
     <xsl:otherwise>
       <xsl:value-of select="concat('0', $number)"/>
     </xsl:otherwise>
   </xsl:choose>
</xsl:template>
 
 
Joel Hughes
joel@xxxxxxxxxxx
ph: +1 905 625 8235
fax: + 1 906 625 6485
 


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