Re: [Dev-luatex] tex.currentgrouplevel

19 Aug 2008

      "Jonathan Sauer"  writes:
...
Hello,
given is the following PlainTeX file:
%&luatex
% \message{\the\currentgrouplevel}
\directlua0{texio.write_nl(tex.currentgrouplevel)}
\bye
This results in:
This is LuaTeX, Version snapshot-0.29.0-2008072919 (Web2C 7.5.7)
(currentgrouplevel.tex
! You can't use `\currentgrouplevel' as tex library index.
l.3 ...lua0{texio.write_nl(tex.currentgrouplevel)}
?
Looking into section 4.1.1 of the manual, currentgrouplevel is not in
the list of tex's integer parameters -- unfortunately. It would be a
quite useful addition in order to create `grouped variables' in Lua
(variables whose previous value is restored at the end of a TeX
group):
-- Assume there are TeX two count registers allocated, `stackIndex'
-- and `groupIndex'
tex.count.stackIndex = 0
tex.count.groupLevel = -1
-- The `grouped variable' stack
local stack = { }
-- Sets a `grouped variable'
function set(name, value)
  if tex.currentgrouplevel > tex.count.grouplevel then
      -- New group opened since the last time. Create a new
stack 
      -- element
      tex.count.stackIndex = tex.count.stackIndex + 1
      stack[tex.count.stackIndex] = { }
      tex.count.groupLevel = tex.currentgrouplevel
-- TODO: Optional: Clear the stack above the new element
to
      -- release old values
  end
-- Add the value
  stack[tex.count.stackIndex][name] = value
end
-- Gets a `grouped variable'
function get(name)
  -- Look through the stack, top to bottom
  for i = tex.count.stackIndex, 1, -1 do
      if stack[i][name] then
      	return stack[i][name]
      end
  end
-- Value not found
  return nil
end
Would not work anyway.  Local values would survive across
\endgroup\begingroup

Whether or not reading the current group level might be interesting is a
different question.  But for this application, it is not sufficient.

What one would need is something like a unique group _id_, and a means
to check whether a certain group id is dead (the group has ended) or
not.  Something like that.

-- 
David Kastrup