EXSLT custom function causes stylesheet to return "too many nested apply-templates calls" error

Question

I tried to implement a "ternary operator" extension function for use in my stylesheet by using EXSLT's func:function element. For compatibility reasons, I have to use XSLT 1.0. I came up with this:

<func:function name="myext:ternary">
  <xsl:param name="expr" />
  <xsl:param name="ifTrue" />
  <xsl:param name="ifFalse" />

  <func:result>
    <xsl:choose>
      <xsl:when test="boolean($expr)"><xsl:value-of select="$ifTrue"/></xsl:when>
      <xsl:otherwise><xsl:value-of select="$ifFalse" /></xsl:otherwise>
    </xsl:choose>
  </func:result>
</func:function>

and it works fine wherever I use it. However, I also tried to implement a substring-after-last function (from here). This code works fine:

<func:function name="myext:substring-after-last">
  <xsl:param name="string" select="''"/>
  <xsl:param name="delimiter" select="$d" />

  <func:result>
    <xsl:choose>
      <xsl:when test="contains($string, $delimiter)">
        <xsl:value-of select="myext:substring-after-last(substring-after($string, $delimiter), $delimiter)"/>
      </xsl:when>
      <xsl:otherwise>
        <xsl:value-of select="$string"/>
      </xsl:otherwise>
    </xsl:choose>
  </func:result>
</func:function>

This way it also works:

[…]
  <func:result>
    <xsl:if test="not(contains($string, $delimiter))">
      <xsl:value-of select="$string"/>
    </xsl:if>
    <xsl:if test="not($string='')">
      <xsl:value-of select="myext:substring-after-last(substring-after($string, $delimiter), $delimiter)"/>
    </xsl:if>
  </func:result>
</func:function>

… but when I try an implementation using the "ternary" function, it does not work;

This doesn't work:

<func:result>
  <xsl:value-of select="myext:ternary(
    contains($string, $delimiter) and not($string = ''),
    myext:substring-after-last(substring-after($string, $delimiter), $delimiter),
    $string
  )"/>
</func:result>

This method results in my stylesheet throwing this error at me:

Error at xsl:apply-templates on line 49 of file:/[my_main_file].xsl:
  Too many nested apply-templates calls
Transformation failed: Run-time errors were reported

I've tried to increase Java's stack size by using the -Xss16m switch, but that just results in Saxon throwing an OutOfMemoryError (Java heap space). The data sets that I send to this function are rather small, so I don't understand where the overflow happens and why it should even be necessary for me to try to increase the stack size.

What am I doing wrong?

If you use Saxon and Java can't you simply use Saxon 9 and XSLT 2.0 which has a user defined functions built-in as a feature? Why do you need to use EXSLT? — Martin Honnen, Jul 31 '13 at 09:38
And with XSLT 2.0 all you want is `tokenize($string, $delimiter)[last()]`. — Martin Honnen, Jul 31 '13 at 09:43
Sorry for not specifying the version, I have to use XSLT 1.0 for corporate compatibility reasons. I have edited the post. — Slampisko, Jul 31 '13 at 10:15

score 0 · Answer 1 · edited May 23 '17 at 10:27

I tried to implement a "ternary operator" extension function

Use a union of a position predicate with a negation predicate variable check as an else statement:

//var[1] | //var[not //var]

Use a concatenation of mutually exclusive expressions as a ternary idiom:

concat("(",substring(translate(., "()-", ""), 1, 3), ")", substring(translate(., "()-", ""), 4, 3), "-", substring(translate(., "()-", ""), 7, 4)))

in XPath number(true()) is 1, while number(false()) is 0 and when second argument of substring() function is greater than actual length of the string, empty string is returned. Hence substring($s1, number(not($condition))*string-length($s1)+1) returns $s1 if $condition is true and empty string otherwise. Concatenating two such expressions in mutually exclusive way gives us conditional strings expression.

References

EXSLT custom function causes stylesheet to return "too many nested apply-templates calls" error

1 Answers1