how to exploit the return of template in a variable?

[abbouh <ab...@ra...>]

i use a template for counting the "ht" node,but the problem is when
i get the return of template to a variable,i have NaN?
this what i use:
...........................
<xsl:variable name="nb_ht">
<xsl:call-template name="test1">
<xsl:with-param name="total" select="0"/>
<xsl:with-param name="pchapmod" select="//chapmod[4]"/>
</xsl:call-template>
</xsl:variable>
..................................



<xsl:template name="test1">
<xsl:param name="total"/>
<xsl:param name="pchapmod" />
<xsl:choose>
<xsl:when test="boolean($pchapmod) and name($pchapmod)='chapmod'">
<xsl:variable name="ht_nb"
select="count(document(concat(string($pchapmod/attribute::docref),'.xml'))//ht)"/>

<xsl:value-of select="$ht_nb"/>
<xsl:text> </xsl:text>
<xsl:call-template name="test1">
<xsl:with-param name="total" select="$total + $ht_nb"/>
<xsl:with-param name="pchapmod"
select="$pchapmod/preceding::chapmod[position() = 1]"/>
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$total"/>
</xsl:otherwise>
</xsl:choose>
</xsl:template>