But I want to know how to pass data to the .tuc file directly from Lua. I think about some complex strings are calculations which are done in each pass and slow down the whole compilation process. Something like:

local function factorial(n)

if in_tuc then -- whatever in_tuc means

   return factorials[n]

else

   ...

   factorials[n] = ...

   return ...

end

end

Is that feasible? Should I use the CLD versions of the TeX macros instead?

Best regards,

Jairo