Restrict custom function parameters

iceandrews · April 10th, 2013, 03:54 PM

Let's say you define a custom function. When declaring a parameter, I could use the "as" flag to define the valid data type on the input parameter of that function. I normally would rely on the XML Schema datatypes (in the xs: namespace) to restrict the input parameter type. But what if I wanted to have a pattern restriction or custom datatype on that parameter?

For example, I want a function that takes a string with the enumeration of "X" and "Y" only. If any other string is passed as an input to that function, the function would 'fail'.

I know you can define a custom type in XML Schema and import that custom data type into your XSLT for use. But can it be done with regular expressions or perhaps some other mechanism?

Code:

<xsl:function name="fns:doSoemthing" as="xs:string">
	<xsl:param name="p1" as="xs:string" />
	<!-- Only 'X' and 'Y' are valid for p1 -->

	<xsl:value-of select="$p1" />
</xsl:function>

mhkay · April 10th, 2013, 04:17 PM

Sure you can do this:

Code:

<xsl:import-schema>
  <xs:schema>
    <xs:simpleType name="X-or-Y">
      <xs:restriction base="xs:string">
        <xs:pattern value="[X|Y]"/>
      </
    </
  </
</
<xsl:function name="f:do" as="X-or-Y">
  <xsl:param name="$in" as="X-or-Y"/>
  <xsl:sequence select="X-or-Y(translate($in, 'XY', 'YX'))"/>
</xsl:function>

The main reason people don't do this, however, is that it's inconvenient, because you can't call f:do('X'), you have to call f:do(X-or-Y('X')). In fact you probably need a namespace for the type as well, I would have to check the rules.

iceandrews · April 10th, 2013, 04:20 PM

Thanks for the reply. That is the method that I expected to have to use. As far as the namespace definitions, I can check the rules as well, but that's a minor detail. I can see how it would be somewhat cumbersome to invoke (not to mention ugly to look at). I can also circle around this by checking the inputs before invoking the functions and throwing exceptions prior to the actual function all. That's much easier done in XSLT, than dealing with custom schema imports.

Thanks again!