Re: [xsl] How do I pass the mode as a string?

The two things that come closest to polymorphism in XSLT (3.0) are (a) the 
template rule despatch mechanism, and (b) higher order functions. Both of these 
can be used to achieve dynamic selection of different functionality based on 
the input data encountered. Exactly how you would apply either mechanism in 
your scenario depends on having a deeper understanding of your specific 
transformation requirement. Modes weren't designed for this requirement and so 
it's hard to give you a forwards directions that doesn't start "If I were you, 
I wouldn't start from here". If you do have to start from here (i.e. you've got 
a collection of interchangeable modes and want to select one of them 
dynamically) then I'm afraid you're stuck with some kind of xsl:choose 
equivalent.

Michael Kay
Saxonica

> On 3 Mar 2020, at 15:38, Kerry, Richard 
> richard(_dot_)kerry(_at_)atos(_dot_)net 
> <xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
>
> Ok,
> Thanks all for the explanations.  I'll look at the alternatives.
> If this was C++, which is what I use most of the time (XSL is infrequent, 
> just when I want to manipulate some XML) I would use some kind of 
> polymorphism to achieve this.  I'd define a couple of one-line functions with 
> the different variables, or calls, and pass the appropriate one to the outer 
> function so they could be run on its results (somewhat garbled, abbreviated 
> explanation, sorry).  I'm not aware of anything in XSL that looks like 
> polymorphism, but I would be interested to know if there was a construct that 
> might be similar, or usable for cases like this one.
> Granted I can't construct variable names dynamically, but I can have a number 
> of variables existing simultaneously and select one and pass it around by 
> address if I need to.  I don't see an analogous construct in XSL, except to 
> use choose/when to select a line of code based on an actual variable.
>
> I could send my examples if that would be best, but I think that would 
> provide a lot of unnecessary code just to show a small bit of context.
> What I am actually trying to do is to get a number of XML files processed.  
> The files are in similar folders, called 'input' and 'output'.  The files' 
> names follow a couple of name patterns, acq_(\d{4}) and out_(\d{4}). There is 
> identical code to scan through the folders and identify the files I want to 
> process (and extract the numbers from the filenames).  They are then passed 
> to apply-templates with the different modes as mentioned.
> So the file scanning, while not especially complicated, is not entirely 
> trivial and I'd like to have it written just once.  And then, because the 
> contents of the files differs in structure, they are handled by different 
> templates, with different modes.
>
>
>
>
>
> Richard Kerry
> BNCS Engineer, SI SOL Telco & Media Vertical Practice
> M: +44 (0)7812 325518
> 2nd Floor, MidCity Place, 71 High Holborn, London, WC1V 6EA
> richard(_dot_)kerry(_at_)atos(_dot_)net 
> <https://webmail.siemens-it-solutions.com/owa/redir.aspx?C=9fb20d019e3e4cb99344d708709a3177&URL=mailto%3arichard.kerry%40atos.net>
>
>
>  
>
>
>
>
>
>
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> From: Michael Kay mike(_at_)saxonica(_dot_)com 
> <xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com>
> Sent: 03 March 2020 11:48
> To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com 
> <xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com>
> Subject: Re: [xsl] How do I pass the mode as a string?
>  
> Section §6.6.2 in the XSLT 3.0 spec states:
>
> The xsl:apply-templates 
> <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.org%2FTR%2Fxslt-30%2F%23element-apply-templates&data=02%7C01%7Crichard.kerry%40atos.net%7Cf54e291885cc4d7f604408d7bf68dcd8%7C33440fc6b7c7412cbb730e70b0198d5a%7C0%7C0%7C637188329424694875&sdata=eSQdcCjN4EO8jORS463GpcDU2L9K0dGwwHP6wU9zJ3o%3D&reserved=0>
>  element also has an optional mode attribute. The value of this attribute 
> must be one of the following:
>
> an EQName 
> <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.org%2FTR%2Fxslt-30%2F%23dt-eqname&data=02%7C01%7Crichard.kerry%40atos.net%7Cf54e291885cc4d7f604408d7bf68dcd8%7C33440fc6b7c7412cbb730e70b0198d5a%7C0%7C0%7C637188329424694875&sdata=Fk%2FK%2FfJKIe1TdwQmwpizrP8xMug12fJUDBRGLfJG17g%3D&reserved=0>,
>  which is expanded as described in 5.1.1 Qualified Names 
> <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.org%2FTR%2Fxslt-30%2F%23qname&data=02%7C01%7Crichard.kerry%40atos.net%7Cf54e291885cc4d7f604408d7bf68dcd8%7C33440fc6b7c7412cbb730e70b0198d5a%7C0%7C0%7C637188329424704871&sdata=J9K12tJfdfAz4JxbQAcj9II%2FfTDTxabxPgUUSo5aHv0%3D&reserved=0>
>  to define the name of a mode
> the token #default, to indicate that the default mode for the stylesheet 
> module 
> <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.org%2FTR%2Fxslt-30%2F%23dt-stylesheet-module&data=02%7C01%7Crichard.kerry%40atos.net%7Cf54e291885cc4d7f604408d7bf68dcd8%7C33440fc6b7c7412cbb730e70b0198d5a%7C0%7C0%7C637188329424704871&sdata=a6iW12SrGH06RlMcl2h9b8dJI3REzfkYOrO5Au8g9z4%3D&reserved=0>
>  is to be used
> the token #unnamed, to indicate that the unnamed mode 
> <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.org%2FTR%2Fxslt-30%2F%23dt-unnamed-mode&data=02%7C01%7Crichard.kerry%40atos.net%7Cf54e291885cc4d7f604408d7bf68dcd8%7C33440fc6b7c7412cbb730e70b0198d5a%7C0%7C0%7C637188329424714867&sdata=i6lQizANc28QMchUjq6CdLldwmM57L1PNleISc%2F%2BDHo%3D&reserved=0>
>  is to be used
> the token #current, to indicate that the current mode 
> <https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.org%2FTR%2Fxslt-30%2F%23dt-current-mode&data=02%7C01%7Crichard.kerry%40atos.net%7Cf54e291885cc4d7f604408d7bf68dcd8%7C33440fc6b7c7412cbb730e70b0198d5a%7C0%7C0%7C637188329424714867&sdata=%2FSSYYInob%2BrZ3Jj5CQK2mqWdJgtpzkoGFsBxM%2FDihKs%3D&reserved=0>
>  is to be used
> It does not allow an expression, and it does not allow an attribute value 
> template. 
>
> It's similar to trying to refer to a variable by name: you can't construct 
> variable names dynamically either, however much you feel it would make your 
> life easier.
>
> You haven't described your problem so it's difficult to suggest a different 
> approach to solving it. Higher-order functions might be the right way.
>
> Michael Kay
> Saxonica
>
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