Re: [xsl] [XSL 3.0] Function that check if a xs:string can be converted as a xs:double

["Michael Kay mike@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Just to clarify: this is not a feature that has been specified in the current
draft of XPath 4.0.

Making types into first class values would indeed be nice, but the work to
define it has not yet been started, let alone finished.

Michael Kay
Saxonica

> On 31 May 2023, at 21:19, Dimitre Novatchev dnovatchev@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> In XPath 4.0 this could be:
>
> fn:castable-as  := function($in as xs:string, $typeName as xs:string)
>                              {  fn:op("castable as")  ($in,  $typeName  )
}
>
> or just:
>
> fn:castable-as  :=    fn:op("castable as")
>
> and this function could be chained within a sequence of other functions.
>
> but I don't think we at present allow  "castable as"  as a possible argument
value of fn:op
>
> What would also be more desirable is to have a type-object (not a type-name
as xs:string) as the 2nd function parameter and in the language.
>
> A type object can have such useful associated functions as parse() and
show() (print / serialize), that one wouldn't even need to have a special
function checking if a value is parsable to a given type. Just parse it and
act correspondingly to the result. Having a type object passed as parameter
one could specify a series of generic operations on any value of that type.
>
> Thanks,
> Dimitre
>
> On Wed, May 31, 2023 at 4:57b/AM Christophe Marchand
cmarchand@xxxxxxxxxxxxxx <mailto:cmarchand@xxxxxxxxxxxxxx>
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx
<mailto:xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>> wrote:
> Hello !
>
> I have to write a function taht take a xs:string as parameter, returns a
xs:boolean, and says true() if string is a valid number, false() otherwise.
>
> Something like
>
> <xsl:function name="f:isNumber" as="xs:boolean">
>   <xsl:param name="expression" as="xs:string"/>
>   <xsl:sequence select="....."/>
> </xsl:function>
> '1' -> true()
> '2' -> true()
> 'foo' -> false()
> 'bar' -> false()
> Rules to be a valid number are the same as those used in number() function.
>
> Any help wil be much appreciated !
>
> Christophe
>
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