Re: fn:slice()

On Sat, 5 Dec 2020 at 08:50, Christian Grün <cg@basex.org> wrote:

> I also believe more and more that Liam’s proposal would be both more
> intuitive and more in alignment with the concept of keyword parameters
> in other languages. In this example…
>
>   declare function do-something(
>     $data as map(*)
>   ) external;
>
>   declare function do-something(
>     $data as map(*),
>     $options as map(*)
>   ) external;
>
>   do-something(data := ..., options := ...)
>
> …one would clearly expect the second function to be called. If keyword
> arguments were equivalent to a single map argument, the code would be
> legal as well, and the first function would be called. This may look
> like an edge case, but maps as arguments are pretty common nowadays.
>
> Things might be safer if we had a dedicated options type:
>
>   declare function do-something(
>     $data as map(*),
>     $options as options(*)
>   ) external;
>
> In that case, the example above would be rejected.
>
> If we stick with the current proposal for keyword arguments, maybe we
> should give them another name than in Python? Maybe "option arguments"
> instead? Or do we have other uses cases, apart from supplying options
> with less characters?
>

If we have something like:

    $options as variadic map(*) (: allow any keyword arguments, optionally
restricted by type :)
    $options as variadic record(a: xs:int, b: xs:string) (: allow only the
specified keyword arguments :)
    $options as variadic some-options-type (: where some-options-type is a
named alias :)

that would make it possible to support variadic array arguments like my
original variadic arguments proposal syntax in xpath-ng:

    $values as variadic array(xs:string)

It could also support sequences for variadic arguments:

    $values as variadic xs:string*
    $values as variadic xs:string+

That way, it is consistent across the 3 types (sequences, maps, and
arrays), and supports both keyword and variadic arguments in a single
syntax.

Reece


> ____________________________________
>
> On Sat, Dec 5, 2020 at 1:31 AM Liam R. E. Quin <liam@fromoldbooks.org>
> wrote:
> >
> > On Fri, 2020-12-04 at 15:23 -0800, Dimitre Novatchev wrote:
> > > So, one will call the function with any map as parameter and this
> > > would be statically OK?
> >
> > Rght now that's more or less what one does with fn:transform. It's a
> > bit of an unfortunate example. Yes, you call it with a map.
> >
> > So Mike's example is exactly what i was suggesting before in this
> > regard, except i want the keywords to map to named arguments so there
> > can be useful static type checking. We would need to allow optional
> > arguments for transform() at least, though, and refer to it e.g. as
> > fn:transform#*
> >
> > Then i could call
> > fn:transform(
> >   source-node: /,
> >   stylesheet-location: "remove-namespaces.xsl"
> > )
> > and have it behave as if it were defined as
> > <xsl:function name="fn:transform">
> >   <xsl:param name="source-node" as="node()" optional="yes" />
> >   <xsl:param name="stylesheet-location" as="xs:anyIRI" optional="yes"
> > />
> >   <xsl:param name="stylesheet-node" as="node()" optional="yes" />
> >
> > (or they could have select attributes, as with templates, to indicate
> > optionality).
> >
> > Any function could then *either* be called in its positional form, *or*
> > with its keyword form; since the same function is called, the arity is
> > the same, and you have to supply all the required (non-optional)
> > parameters.
> >
> > Mike i think is proposing something slightly different: that keyword
> > parameters get put into a map that must then be the only argument of
> > the function: fn:transform#1 takes a map as input today, and he says
> > it'd be unchanged. I'd rather see the one or two unusual functions
> > changed and be able to use keyword parameters everywhere.
> >
> > Liam
> >
> >
> >
> >
> > --
> > Liam Quin, https://www.delightfulcomputing.com/
> > Available for XML/Document/Information Architecture/XSLT/
> > XSL/XQuery/Web/Text Processing/A11Y training, work & consulting.
> > Barefoot Web-slave, antique illustrations:  http://www.fromoldbooks.org
> >
> >
>
>