[Dev-luatex] tex.currentgrouplevel

19 Aug 2008

      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

Jonathan

[Dev-luatex] tex.currentgrouplevel

Jonathan Sauer