[NTG-context] Writing to .tuc directly from Lua

Hi, list. I read about this: https://www.mail-archive.com/ntg-context@ntg.nl/msg60217.html 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