Better Lua string-parsing

[anaseskyrider]

The current method you use to extract the substrings of the dice notation in Lua is very inefficient (and pollutes the namespace with globals). This stuff is what pattern-matching is for and reduces most of the work to just a couple lines of code and some checks. Over 1,000,000 iterations with my method, I saw improved execution speeds of around 270%.

Getting a new math seed every time the roll is called is also only useful for command-line executions of this script in quick-succession, and is not usable (and counter-productive!) for video game applications where the script doesn't reseed with every execution. I recommend replacing that with a bool.

function roll(diceString, reset)
  -- get dice info
  local pattern = "^(%d*)[Dd](%d+)([-+/*]?)([+-]?%d*)"
  local dice,size,op,mod = diceString:match(pattern)
  dice = (dice=="" and 1) or tonumber(dice)
  size = (size=="" and 1) or tonumber(size)
  op = (op=="" and nil) or op -- allows for easy checks with "if op then ... end"
  mod = (mod=="" and nil) or tonumber(mod)

  if reset then
    -- the os.time() is commonly cited as a good way to randomly
    --    seed randomness. However, die rolls aren't random in
    --    this case when running the script multiple times in one
    --    second. FOund this seeding technique on:
    --    https://www.reddit.com/r/lua/comments/1b5qg3/need_help_with_truly_random_number_generator/c940pyj/
    math.randomseed(os.time() + tonumber(tostring({}):sub(8)))
  end

  -- start rolling
  local result = 0
  for i=1, dice do
    result = result + math.random(1, size)
  end

  -- apply modifiers to total
  if op and mod then
    -- could add elifs for * and /
    if op == "+" then
      result = result+mod
    elseif op == "-" then
      result = result-mod
    end
  end
  return result
end

[brianherbert]

Thanks for the detailed write up! Totally unexpected in this repo and appreciate the critique for my first lua script. If you'd like to submit a pull request, I'll happily incorporate your changes.