Check Pandoc Version in LUA for 2.1+

check.lua

--[[
  This function tests the pandoc version againt a target version
  For Pandoc 2.7.3, PANDOC_VERSION >= "2.8" would be enough but before 2.7.3
  it is a table object
]]
local function pandocAvailable(target)
  -- this function only work for Pandoc 2.1 and above. It returns false is not
  if not PANDOC_VERSION then return false end
  assert(target, "No target version specified in pandocAvailable.")
  -- checking each version number
  -- EPOCH.MAJOR.MINOR.PATCH (https://pvp.haskell.org)
  for i = 1,4 do
    -- some versions do not have all numbers
    if not PANDOC_VERSION[i] or not target[i] then break end
    if PANDOC_VERSION[i] < target[i] then return false end
    if PANDOC_VERSION[i] > target[i] then return true end
  end
  return true
end

Thanks for the tip about Pandoc version scheme @tarleb!