Re: [xsl] import, include, and packages?

Subject: Re: [xsl] import, include, and packages?
From: "Michael Kay mike@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 23 Apr 2020 17:00:28 -0000
> 1. I think the advantage of using <xsl:package> over <xsl:import> and
<xsl:include> for my case (importing a single function [but see below about
arity]], from a package that does not import anything itself) is that I can
expose only the function that I want to expose, and not any other named
components of the imported package (variables, helper functions, etc.). If
that understanding is correct, it does sound like an advantage. (I want to be
able to run the code in Saxon HE, so being able to precompile the package,
which would be a benefit under other circumstances, would not be relevant in
this case.)

Certainly, being able to restrict what you expose is one of the benefits of
using packages. Also, you have much more control over what can be overridden,
and how; it's the fact that overrides must be type-compatible that enables
packages to be separately compiled.
> 2. I don't understand how (or whether it is possible) to import packages
without setting up a configuration file. If it isn't, that would seem to be a
disadvantage for my use case, since anyone else who wanted to use my function
library would have to set up a configuration, as well., and not just get a
copy of the package file itself If I have understood correctly, the spec seems
to say that the configuration is implementation-dependent, so if one is
needed, where would I find documentation about how to set it up for use by
Saxon, both at the command line and inside <oXygen/>? If a configuration setup
is not requiredbthat is, if it is possible to specify the file-system
location of the imported package directly inside the importing oneb how do I
specify the location of the imported package in <xsl:use-package>, given that
I would want the path to be relative to the importing stylesheet? Is the
procedure for doing that the same as with <xsl:include> and <xsl:import>?

Configuration files are an artefact of the Saxon implementation, nothing to do
with the spec, which leaves the mechanism for locating a package
implementation-dependent. You can't specify a relative path location for a
used package (though, as I'm beginning to understand the JS common module
system better, I think I can see how we could add that option). But there are
alternatives to using a configuration file; you can use
XsltCompiler.importPackage() in the s9api API, or the -lib option on the
Transform command line.
> 3. On a semi-related topic, I want my function to have one-argument and
two-argument versions. Since function parameters cannot be optional, I think a
fairly straightforward way to do this would ge to put the code in the
two-argument version, and have the one-argument version supply a default for
the missing argument and then use it to pass the call along to the
two-argument version. Is this the best way to deal with optional function
Yes. (In my paper at XML Prague -- see B'3.3) I proposed adding
syntactic sugar to make this easier.)

Michael Kay

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