reader.lua

function readNumber(question, ...)
  print(question)
  local arg = {...}
  local max = 9999999
  local min = -9999999
  if(arg[1] ~= nil) then min = arg[1] end
  if(arg[2] ~= nil) then max = arg[2] end
  local n
  repeat
    local valid = false
    local r = read()
    n = tonumber(r)
    if (n~=nil) then
     if(min >= n) then
       print("Input needs to be higher than "..arg[0])
      end
      if(max < n) then
        print("Input needs to be lower than "..arg[1])
      end
      if(min < n and max >= n) then
        valid = true
      end
    else
      valid = true
    end
   end
  until(valid)
end

readNumber("a number")
readNumber("a number",0,100)