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Re: Why does the addition of one (1) to a positiveInte

Subject: Re: Why does the addition of one (1) to a positiveInteger produce an integer?
From: Michael Kay <mike@xxxxxxxxxxxx>
Date: Sun, 29 Aug 2010 21:46:09 +0100
Re:  Why does the addition of one (1) to a positiveInte
When I run this I get an error, "The argument to f:iter is xs:positiveInteger, the supplied value is xs:integer"

What is the rationale for this? After all, if I add one (1) to any positiveInteger the result must be a positiveInteger.


There might be logic for saying that the result of xs:positiveInteger + xs:positiveInteger should always be xs:positiveInteger, but a rule that says xs:positiveInteger + xs:integer gives xs:positiveInteger provided that the xs:integer is positive (or provided it is greater than the negation of the first argument?) would be rather arbitrary.


Generally I would advise against writing a function that expects subtypes of xs:integer as an argument, because you will never be able to supply the argument as a simple literal. These types were designed for validation, not for type-checking programs. That's why, for example, the standard functions insert() and remove() declare the expected type as xs:integer rather than xs:positiveInteger. (It's also why in XSLT 2.0 types such as xs:positiveInteger were excluded from the set of types recognized by a basic XSLT processor). If you want to reject negative integers, do it by conditional code in the body of the function, not by means of the type signature.

Michael Kay
Saxonica

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