[luatex] Processing every letter in math

[Esger Renkema]

>How can I process every single letter in math? Processing
>glyph nodes in text is more or less trivial, and to some
>extent even in-line math (surrounded by 'math' type nodes),
>but processing math, including displays, sub/superscripts,
>fractions, radicals. etc.? From the manual I think the
>solution must be the node.mlist_to_hlist and the
>corresponding callback [...]

That is the correct callback. But at this point, you are still working 
on noads, not nodes, so ids 0 and 1 will not be the only ones containing 
nested node lists.

See the following code, taken from minim-math.lua:

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local listmathfields = { 'head', 'nucleus', 'sub', 'sup', 'accent', 
     'bot_accent', 'display', 'text', 'script', 'scriptscript', 'num', 
     'denom', 'degree', 'next' } -- note that ‘next’ should be last!

local function noad_iterator(head)
     local nodelist = { up=nil, current=head }
     return function()
         if nodelist == nil then return nil end
         local n = nodelist.current
         nodelist = nodelist.up
         for _,f in pairs(listmathfields) do
             if node.has_field(n, f) and n[f] ~= nil then
                 nodelist = { up=nodelist, current=n[f] }
             end
         end
         return n
     end
end

local function inspect_noads(h,d,n)
     for nd in noad_iterator(h) do
         if nd.id == node.id('math_char') then
             -- TODO: whatever you wish
         end
     end
     node.mlist_to_hlist(h,d,n)
end

callback.register('mlist_to_hlist', inspect_noads)

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