Saxon » SaxonJS

As reported by Martin, the failure with SaxonJS 2 is different:

xslt3 -t -s:Downloads\evaluationTest.xml -xsl:Downloads\validation.xslt
SaxonJS 2.5 from Saxonica
Node.js version v16.17.1
Compiling stylesheet C:\Users\marti\Downloads\validation.xslt
Stylesheet compilation time: 0.249s
Asynchronous transform with options: stylesheetText={"N":"package","version":"20",(string), stylesheetBaseURI=file://C:/Users/marti/Download(string), stylesheetParams=[object Object](string), outputProperties=[object Object](string), extraOptions=[object Object](string), destination=stdout(string), baseOutputURI=file://C:/Users/marti/(string), logLevel=2(string), sourceFileName=file://C:/Users/marti/Download(string),
SEF generated by SaxonJS 2.5 at 2023-05-01T22:27:47.954+02:00
 in root of document
<?xml version="1.0" encoding="UTF-8"?>
<innings>
   <number>1</number>
   <battingSide>yorkshire</battingSide>
   <fieldingSide>lancashire</fieldingSide>
   <over>
      <bowler>1</bowler>Transformation failure: Error XTTE0570 at validation.xslt#39
  Required item type of value in 'xsl:variable name="Q{}read_function"' expression is (function(element(*)) as element(*)?); supplied value is anonymous function (arity 1)
Error XTTE0570 at validation.xslt#39
  Required item type of value in 'xsl:variable name="Q{}read_function"' expression is (function(element(*)) as element(*)?); supplied value is anonymous function (arity 1)

And in fact, this error is correct, though the error message does not give quite enough information to make this clear. The supplied anonymous function will not pass the type checking because its function type is not a subtype of function(element(*)) as element(*)?

The signature of the supplied anonymous function is either function(element(innings)) as element(side) or function(element(over)) as element(player), as specified in the function declarations in the source evaluationTest.xml.

But for function types, function(A) as B is a subtype of function(C) as (D) requires that B is a subtype of D, and C is a subtype of A, not the other way round (see https://www.w3.org/TR/xpath-31/#id-sequencetype-subtype).

To avoid this type checking error, I think it is necessary to be less specific for the types of the arguments in the XPath function declarations in evaluationTest.xml:

• use function($instance as element()) as element(side) instead of function($instance as element(innings)) as element(side) on line 6
• use function($instance as element()) as element(player) instead of function($instance as element(over)) as element(player) on line 12

To then get the test to run correctly, I also needed to correct line 14 in evaluationTest.xml:

• $lib?readRel($instance/parent::element(innings), 'fieldingSide') rather than $lib?readRel($instance, 'fieldingSide')

Can now confirm that the new XSLT30 tests evaluate-051 and evaluate-052 also pass with SaxonJS 2.

Getting the types for function items can be pretty tricky as the arguments reverse the sense of 'subtype' (It can help to think of two sets of Venn diagrams, one in the range, i.e. function output, and on one in each of the argument domains.) To be a same-or-subtype the (output) range must really be a same-or-subtype of the required type of the function call use. But for the all the arguments it must be the other way round: the expected type of each function argument must be self-or-supertype of the supplied call argument.

This of course becomes even more convoluted in higher-functions where the arguments to the function themeselves are functions and potentially their arguments type 'flip' the subtype sense yet again.