[NTG-context] Using Lua to format lecture titles

17 Aug 2021

      I'm trying to create a new lecture environment starting from the base
section.

I'd like its title to be `Lecture <number>: <title>` if a title is
provided, and `Lecture <number>` if it isn't. This title should also be
reported in the left footer and in the table of contents.

This is the code I have so far:

```
\definehead
  [lecture]
  [section]

\setuphead
  [lecture]
  [
    command=\Lecture,
    style=\bfc,
  ]

\setuplabeltext
  [lecture={Lecture}]

\define[2]\Lecture{\ctxlua{
  userdata.format_lecture_title({
    label = context.labeltext('lecture'),
    number = [==[#1]==],
    title = [==[#2]==],
  })
}}

\setupfootertexts
  [\ctxlua{
    userdata.format_lecture_title({
      label = context.labeltext('lecture'),
      number = context.getmarking({'lecturenumber'}),
      title = context.getmarking({'lecture'}),
    })
  }]
  [pagenumber]

\startluacode
  userdata = userdata or {}

  function userdata.format_lecture_title(args)
    if args.title and args.title ~= '' then
      context('%s %s: %s', args.label, args.number, args.title)
    else
      context('%s %s', args.label, args.number)
    end
  end
\stopluacode

\setupcombinedlist
  [content]
  [list={lecture}]

\setuplist
  [lecture]
  [
    alternative=c,
    command=\Lecture, % this seems to have no effect?
  ]

\starttext

\completecontent

% Both title and left footer should be 'Lecture 1: Foo'
\startlecture [title={Foo}]
Foo bar baz
\stoplecture

\page

% Both title and left footer should be 'Lecture 2'
\startlecture []
Foo bar baz
\stoplecture

\stoptext
```

Unfortunately none of them are reported correctly. The title in the body is
formatted simply as `Lecture`, the one in the left footer is formatted as
`Lecture<number><title>`, and the one in the table of contents isn't
affected at all.

What am I doing wrong?

[NTG-context] Using Lua to format lecture titles

noib3