Tonumber returns nil in dynamical snippet

[gsadovski]

Dear all,

I am trying to make a conditional piece of snippet that prints node 2 inside node 3, if node 1 is given an year older than 2007. The issue seems to be the function tonumber returning nil from the get-go. If I remove tonumber I get "trying to compare a string to a number" error, which makes sense. I am very much a beginner at Lua, and even though I have a hunch that the problem might be tonumber being evaluated when the snippet expands (node 1 still lacking a input), I have no idea how to fix it (if that is indeed the issue). Could the more experienced, please, give me some ideas?

eprint_format = function(args)
  local year = tonumber(args[2][1])
  local eprintclass = args[1][1]
  if year == nil then
    return sn(nil, { t('not working') })
  else
    if
        year < 2007 then
      return sn(nil, { t(eprintclass .. '/') })
    else
      return sn(nil, { t('') }) -- If the year is not smaller than 2007, insert nothing
    end
  end
end

return{
   s({
      trig = 'eprint',
      name = 'testing conditional',
      desc = 'expands to subsnippet',
      snippetType = 'autosnippet'
    },
    fmta([[
year = {<>},
eprintclass = {<>},
eprint = {<><>},
]], { i(1), i(2), d(3, eprint_format, { 1, 2 }), i(4) })
  ),
}