Re: Reading ConTeXt metadata values into Lua

[Ramkumar KB via ntg-context <ntg-context@ntg.nl>]

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Hans / Wolfgang,

Thank you for your quick feedback and the tips. Yes, this works for now.

In general, I will try to avoid going into such "deep-end" APIs (at least
for now, until such time I read all the manuals in depth!). IMHO, the
standard ConTeXt system is itself quite powerful for 98% of the Typesetting
usecases.

best regards,
Ramkumar


On Sat, Oct 16, 2021 at 4:59 PM Hans Hagen via ntg-context <
ntg-context@ntg.nl> wrote:

> On 10/16/2021 10:33 AM, Wolfgang Schuster via ntg-context wrote:
> > Ramkumar KB via ntg-context schrieb am 16.10.2021 um 06:00:
> >> Hello All,
> >>
> >> I was trying to read the value of '\totalnumberofpages' into lua to do
> >> something with it. As an example, see below.
> >>
> >> Now, as I understand it, my example would not work as TeX gets the
> >> first go at this and therefore the variable 'pages' is the string
> >> '\totalnumberofpages' and not the actual value itself. And Lua cannot
> >> process this "calculation".
> >>
> >> I tried to go thru the manual - *cld-mkiv.pdf *- in the distro but
> >> could not catch on how to read a metadata value (not print). I am sure
> >> that I am missing a small trick somewhere (or is it something more
> >> involved?).
> >>
> >> \startluacode
> >> function myFancyCalculations(pages)
> >>   -- some fancy stuff but as an example
> >> local myCal = tonumber(pages) + 1
> >> return myCal
> >> \stopluacode
> >> \starttext
> >>
> >> \blah
> >>
> >> \ctxlua{context(myFancyCalculations("\\totalnumberofpages"))}
> >>
> >> \stoptext
> >
> > Everything gets easier when you use the Lua functions to access the
> > counter values but be aware the values can be wrong when you're at a
> > page break.
> >
> > \startbuffer[pagenumber]
> > \startluacode
> > context.starttabulate()
> >      context.NC()
> >          context("Current page")
> >      context.EQ()
> >          context(structures.counters.get("realpage",1,"number"))
> >      context.NC()
> >      context.NR()
> >      context.NC()
> >          context("Last page")
> >      context.EQ()
> >          context(structures.counters.get("realpage",1,"last"))
> >      context.NC()
> >      context.NR()
> > context.stoptabulate()
> > \stopluacode
> > \stopbuffer
> >
> > \starttext
> >
> > \dorecurse
> >      {\randomnumber{5}{10}}
> >      {\getbuffer[pagenumber]
> >       \page}
> >
> > \stoptext
>
> As addendum ... The problem in general with macros is that one doesn't
> really knows by looking at the name what actually happens when it
> expands, which can be a lot. Now, because \totalnumberofpages is
> supposed to 'return' a number and not typeset something styled (which
> itself involved macro expansion) you can actually do this:
>
> \startluacode
> local n = tokens.getters.macro("totalnumberofpages",true)
> print(">>>",type(n),n)
> \stopluacode
>
> but beware of the fact that you actually get back a string:
>
> \startluacode
> local n = tokens.getters.macro("totalnumberofpages",true)
> print(">>>",type(n),n)
> local n = tonumber(n)
> print(">>>",type(n),n)
> \stopluacode
>
> etc etc
>
> Hans
>
> -----------------------------------------------------------------
>                                            Hans Hagen | PRAGMA ADE
>                Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>         tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
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