XSLT Logic Overwrite a temporary variable - xslt

Question

How we can achieve below logic.
The UniqueID is the temporary variable.PALLET_NUMBER is coming from input.
if PALLET_NUMBER!=NULL then
UniqueID=substring (PALLET_NUMBER, 10)
if PALLET_NUMBER =NULL then
UniqueID=substring (CARTON_NUMBER, 7)
we can get the value of UniqueID from the above two conditions.These things happen in iteration loop.How we can overwrite the UniqueID temporary variable.
bacause later There is a condition we need to put like
<foreach>
If previous UniqueID != current UniqueID then
<Some code>
<IF>
</foreach>

Answer 1

You cannot overwrite variable in xslt.
You may want to look up xslt extension functions to achieve your goal.

Answer 2

As Treemonkey, says, it's not possible to overwrite variables, but you can achieve something like you describe using recursion:
Suppose you had something like this:
<xsl:for-each select="my/node/isNamed/something" />
You could do this instead:
<xsl:variable name="items" select="my/node/isNamed/something" />
<xsl:apply-templates select="$items[1]">
<xsl:with-param name="remainder" select="$items[position() > 1" />
</xsl:apply-templates>
<!-- Separate template -->
<xsl:template match="something">
<xsl:param name="remainder" />
<xsl:param name="lastId" />
<xsl:variable name="uniqueId" select="..." />
<!-- Contents of the xsl:for-each -->
<xsl:apply-templates select="$remainder[1]">
<xsl:with-param name="remainder" select="$remainder[position() > 1]" />
<xsl:with-param name="lastId" select="$uniqueId" />
</xsl:apply-templates>
</xsl:template>