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Re: strong typed variable with restriction ?

Subject: Re: strong typed variable with restriction ?
From: Michael Kay <mike@xxxxxxxxxxxx>
Date: Wed, 02 Feb 2011 11:21:59 +0000
Re:  strong typed variable with restriction ?
There seem to be two separate questions here.
I have a xsl:function which :
- must return a element()
- has a string param "foobar".

I typed $foobar as xs:string but I'd like to restrict the possible values to "foo" or "bar".
I know it's possible to define such a constrain in a xsd schema, but is there a way to do that in xpath2 ?

You can declare a local type in your stylesheet:


<xsl:stylesheet xmlns:fb="urn:local:foobar" ....>

<xsl:import-schema>
<xs:schema targetNamespace="urn:local:foobar">
<xs:simpleType name="foobarType">
<xs:restriction base="xs:string">
<xs:enumeration value="foo"/>
<xs:enumeration value="bar"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
</xsl:import-schema>

<xsl:function name="igs:get-css-rule" as="element()">
<xsl:param name="foobar" as="fb:foobarType"/>
  ....

Note that when calling the function, you can't pass a string directly: you will have to cast ot to fb:foobarType first.




This typing is important because the returned element() is selected from a xsl:choose on $foobar value (with no otherwise) :

My code looks like :
<xsl:function name="igs:get-css-rule" as="element()">
<xsl:param name="foobar" as="xs:string"/> <!--(foo|bar)-->
<xsl:choose>
<xsl:when test="$foobar='foo'">
<xsl:sequence select="igs:get-my-foo-item()"/>
</xsl:when>
<xsl:when test="$css='bar'">
<xsl:sequence select="igs:get-my-bar-item()"/>
</xsl:when>
</xsl:choose>
</xsl:function>

And I get such a parsing error on my xslt :
XTTE0570: Conditional expression: If none of the conditions is satisfied, an empty
sequence will be returned, but this is not allowed [...]

Typing the parameter unfortunately won't solve this problem. The processor isn't clever enough to work out that the implicit "otherwise" branch will never be executed, so it will still report a type error to the effect that the implicit "otherwise" branch returns a value (namely the empty sequence) which doesn't conform to the required return type of the function. (There has been some suggestion that Saxon's type checking here is too pessimistic; the type error should be raised dynamically if this branch is taken, not statically). The easiest way around this is probably to change the last xsl:when condition to an xsl:otherwise.


Michael Kay
Saxonica

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