100 Languages Speedrun: Episode 89: MoonScript

MoonScript is CoffeeScript for Lua.

It doesn't seem to be maintained much anymore. The most recent release was back in 2015, and it doesn't work with the latest Lua. You can still run it with non-release version, with luarocks install moonscript --dev.

Hello, World!

Hello World is as simple as it gets. Newline is automatically inserted:

#!/usr/bin/env moonprint "Hello, World!"

$  ./hello.moonHello, World!

FizzBuzz

MoonScript uses indentation base syntax. For loops use Lua syntax instead of .. ranges.

#!/usr/bin/env moonfor i = 1, 100  if i % 15 == 0    print "FizzBuzz"  elseif i % 5 == 0    print "Buzz"  elseif i % 3 == 0    print "Fizz"  else    print i

Fibonacci

MoonScript has nice syntax for defining functions with two kinds of arrows, and implicit return. There's also beautiful string interpolation.

#!/usr/bin/env moonfib = (n) ->  if n <= 2    1  else    fib(n-1) + fib(n-2)for n = 1,20  print "fib(#{n})=#{fib(n)}"

Unicode

Unicode is broken in Lua, and MoonScript does not fix it. Method call syntax is also really weird with a backslash, as . is taken for regular function call (that doesn't pass extra self as first argument).

#!/usr/bin/env moonprint "Hello"\len()print "w"\len()print ""\len()print "w"\upper()print "w"\lower()

$ ./unicode.moon574Ww

Person class

It's just an empirical fact that people overwhelmingly hate prototype-based inheritance, and want classes. MoonScript provides the same two main things as CoffeeScript - nicer syntax, and class-based OOP.

#!/usr/bin/env moonclass Person  new: (@name, @surname, @age) =>  __tostring: =>    "#{@name} #{@surname}"maria = Person("Maria", "Ivanova", 25)print "#{maria} is #{maria.age} years old"

$ ./person.moonMaria Ivanova is 25 years old

This is fairly nice. There's no default __tostring, it's just table: 0xADDRESS, so we really should provide something. Constructors auto-assign any @arguments, so you don't need to do the boring thing every time. I'm actually a bit disappointed in Ruby for not doing this obvious thing 80% of the time:

class Person  new: (name, surname, age) =>    @name = name    @surname = surname    @age = age

Vector

We can do enough operator overloading to make vectors work. Which exact operators can be overloaded depends on Lua version (and games often ship with older versions):

#!/usr/bin/env moonclass Vector  new: (@x, @y) =>  __tostring: => "<#{@x},#{@y}>"  __add: (other) => Vector(@x + other.x, @y + other.y)  __eq: (other) =>    @__class == other.__class and @x == other.x and @y == other.ya = Vector(20, 60)b = Vector(400, 9)c = a + bprint aprint bprint cprint c == Vector(420, 69)

$ ./vector.moon<20,60><400,9><420,69>true

This doesn't really help with printing plain Lua tables like arrays, just MoonScript classes.

Wordle

Let's do Wordle.

The first problem we run into is that Lua lacks the most basic functions like string.split, string.contains etc. There's one included as import in moonscript.util, but it leaves extra "" at the end, so we need to remove it.

This code looks bad because Lua desperately needs a better standard library, and MoonScript does not come with one:

#!/usr/bin/env moonimport split from require "moonscript.util"readlines = (path) ->  file = io.open("wordle-answers-alphabetical.txt")  text = file\read("*a")  file\close!  lines = split text, "
"  table.remove(lines) -- remove empty "" at the end  linesrandom_element = (array) ->  array[math.random(#array)]class Wordle  new: =>    @words = readlines("wordle-answers-alphabetical.txt")  report: (word, guess) =>    for i=1,5      letter = guess\sub(i,i)      if word\sub(i,i) == letter        io.write ""      -- non-regexp string.contains?      elseif word\find(letter, 1, true)        io.write ""      else        io.write ""    io.write "
"  __call: =>    word = random_element(@words)    guess = ""    while guess != word      io.write "Guess: "      guess = io.read!      if #guess == 5        @report(word, guess)      else        print "Guess must be 5 letters long"game = Wordle()game()

$ ./wordle.moonGuess: audioGuess: stoneGuess: loverGuess: vowel

Should you use MoonScript?

It's unfortunately abandoned, and it's hard to recommend abandoned languages.

Otherwise there's a pretty obvious use case. So many games are coded in Lua, and MoonScript compiles into fairly clean Lua, so if you want to mod Lua-based games like Factorio, maybe MoonScript would be a reasonable idea.

I don't really recommend Lua or MoonScript for anything new, but as a game modder you're stuck with whatever game developers decided to use, so having this an as option is nice.

If anyone feels like giving this project a shot, and release a new working version, maybe it would be of some use for modders.

I feel like it would provide a lot more value if such revived MoonScript also came up with decent standard library comparable with what Ruby, JavaScript, and Python have.

Code

All code examples for the series will be in this repository.

Code for the MoonScript episode is available here.