Lua for Rubyists

Enrique García Cota (@otikik)

madrid-rb, 2014-01

2 main parts:

Applications

Comparison

It's Lua, not LUA

SOL ⇒

Simple Object Language

Lua ⇒

“Moon” in Portuguese

(No Initials)

Part 1: Applications

www.techempower.com/benchmarks

www.techempower.com/benchmarks

Key-value data store

require "redis"
redis = Redis.new('localhost', 6379)

redis.set("name", "peter")
name = redis.get("name") # "peter"

redis.set("age", "25")
new_age = redis.incr("age") # 26

Concurrent, but single threaded

counter = redis.get('counter')

redis.incr('counter') if counter.is_a? Numeric

script = <<-EOS
  local counter = redis.call("GET", KEYS[1])
  if type(tonumber(counter)) == "number" then
    return redis.call("INCR", KEYS[1])
  end
EOS

redis.eval(script, ["counter"])

brew install vim --with-lua

-or-

brew install macvim --with-lua

                    Startup     Speed

      Vim script    0           1.498s
      Python        0.0166s     0.027s (2000%)
      Lua(jit)      0.0002s     0.001s (1152000%)

Corona SDK

coronalabs.com/i-want-to-build/games/

coronalabs.com/i-want-to-build/business-apps/

www.love2d.org

Part 2: Comparison

Generalities

Yukihiro Matsumoto

A general-purpose language to make programmers happy

Roberto Ierusalimschy

Portable, powerful, embeddable, fast.

Implementations

Ruby

MRI (1.8.7, 1.9.x, 2.x)

JRuby

Rubinius

Lua

Lua (5.0, 5.1, 5.2)

LuaJIT

eLua

Feel

# ruby
name   = 'Peter'
age    = 35
genter = :male

puts "#{name} is a #{age} years old #{gender}"

doc = %{
  Lorem ipsum dolor sit amet
}

-- lua
local name   = 'Peter'
local age    = 35
local genter = "male"

print(name .. " is a " .. age .. ' years old ' .. gender)

local doc = [[
  Lorem ipsum dolor sit amet
]]

Ruby comments:

# a single-line comment in ruby

=begin
  a multi-line comment in ruby
=end

Lua comments:

-- a single-line comment in Lua

--[[
  a multi-line comment in Lua
]]

#ruby
h = {a: 1, b: 2}
puts h[:b] # 2
puts a.class.name # 'Hash'

a = [1,2,3,4]
puts a[0] # 1
puts a.class.name # 'Array'

-- lua
local h = {a = 1, b = 2}
print(h['b'])  -- 2
print(h.b)     -- also 2
print(type(b)) -- 'table'

local a = {1,2,3,4}
print(a[1]) -- 1
print(type(a)) -- 'table'

Lua tables:

• Arrays
• Hashes
• Structs
• References
• Environments
• Objects
• ...

#ruby




def sum(a,b)
  a + b
end

#ruby

module Kernel

  private # ??
  def sum(a,b)
    a + b
  end
end

-- lua

function sum(a+b)
  return a + b
end

print(type(sum))   -- 'function'
print(type(type))  -- 'function'
print(type(print)) -- 'function'

-- lua

_G.sum = function(a+b)
  return a + b
end

print(type(_G)) -- 'table'

-- lua

local sum = function(a+b)
  return a + b
end

Lua functions:

• Values
• Blocks
• Scopes
• Iterators
• Generators
• ...

Ruby feels ♡ ♡ ♡

even_numbers = (1..10).select(&:even?)

tweets.delete_if{ |t| t.older_than? 1.week }

Lua feels like super-javascript

// Very little of this stuff:
[9,10,1,2].sort()
> [1,10,2,9]

“Learn Lua in 15 minutes” http://tylerneylon.com/a/learn-lua/

Size

Lines of code

git clone https://github.com/ruby/ruby.git
rm -rf ruby/benchmark ruby/bootstraptest ruby/doc \
       ruby/ext ruby/sample ruby/test ruby/tool
cloc ruby

⇒ ~650k (C, C++, Ruby)

git clone https://github.com/LuaDist/lua.git
cloc lua/src

⇒ ~15k (C99)

Ruby core:

$ irb
> a = Object.constants.map{|c| Object.const_get(c)}
 => [ ... ]

> b = a.select{|c| c.is_a? Class}
 => [ Object, Module, Class, BasicObject, Method,
      NilClass, String, Symbol, Regexp, Range,
      Time, Date, File, Dir, TrueClass, FalseClass,
      Numeric, Integer, Fixnum, Float, Bignum,
      Rational, Complex, Thread, Fiber, ...
    ] (73)

> b.map{|c| c.methods.count}.inject(:+)
  => 7112

> b.map{|c| c.public_methods(false).count}.inject(:+)
  => 399

Ruby Stdlib:

www.ruby-doc.org/stdlib-2.1.0

     set         yaml       minitest     erb
     base64      csv        mutex        webrick
     date        json       zlib         net/*
     fileutils   matrix     curses       socket
     pp          profile    rss          uri
                        ...

                       (~109)

• Presentation: “Ruby: Batteries Included”:

  http://www.confreaks.com/videos/2347

Ruby ⇒ gems

rubygems.org

~70000 gems

Lua:

Types (~7)

string, number, table, boolean, function, thread, nil

Libraries (~7)

string, math, table, os, io, coroutine, debug

Top-level functions (~30)

    assert          load        pcall     setmetatable
    collectgarbage  loadfile    print     tonumber
    dofile          loadstring  rawequal  tostring
    error           module      rawget    type
    gcinfo          newproxy    rawset    xpcall
    getfenv         next        unpack
    getmetatable    require     select
    ipairs          pairs       setfenv

Lua ⇒ rocks

luarocks.org

~700 rocks

Batteries included

Artillery battery: a unit of guns, mortars, rockets or missiles so grouped in order to facilitate better battlefield communication and command and control

Conclusion

Ruby is great.

Lua is great.

Questions?

Enrique García Cota (@otikik)

madrid-rb

Thank you! ☆