seven-more-languages-in-seven-weeks/slides/lua.org

Seven More Languages in Seven Weeks

Introduction

Introduction

Lua   BMCOL

LUA

A powerful, fast, lightweight, embeddable scripting language

Indiana Jones   BMCOL

Day 1

Day 1: The Call to Adventure

• Installing Lua

• Exploring with the REPL

  • Syntax
  • Types
  • Functions

Syntax

Whitespace doesn't matter

Types

• Lua is dynamically typed
• No integers (all numbers are 64-bit floats)
• nil is its own type

Functions

• Functions are first-class values
• Arguments are flexible
• Support arbitrary numbers of arguments
• Support arbitrary numbers of results
• Lua does tail call optimization

Variables

Lua variables are global by default

Excercises

Exercises

Notes   B_note

• Lua Users Wiki
• Programming in Lua (First Edition)
• Lua 5.1 Reference Manual
• The difference between a while and repeat loop

Day 2

Day 2: Tables All the Way Down

Tables as Dictionaries

  book = {
     title  = "Grail Diary",
     author = "Henry Jones",
     pages  = 100
  }

  book.stars  = 5
  book.author = "Henry Jones, Sr."

Tables as Arrays

• Lua counts array indices starting at 1

  medals = {
     "gold",
     "silver",
     "bronze"
  }

  medals[4] = "lead"

Metatables

Left   BMCOL

  function table_to_string(t)
     local result = {}

     for k, v in pairs(t) do
        result[#result + 1] = k .. ": " .. v
     end

     return table.concat(result, "\n")
  end

  greek_numbers = {
     ena  = "one",
     dyo  = "two",
     tria = "three"
  }
  mt = {
     __tostring = table_to_string
  }
  setmetatable(greek_numbers, mt)

Right   BMCOL

  > =greek_numbers
  ena: one
  tria: three
  dyo: two

OOP

Left   BMCOL

  Villain = {
     health = 100,
     new = function(self, name)
        local obj = {
           name   = name,
           health = self.health
        }
        setmetatable(obj, self)
        self.__index = self
        return obj
     end,
     take_hit = function(self)
        self.health = self.health - 10
     end
  }

Right   BMCOL

  SuperVillain = Villain.new(Villain)

  function SuperVillain.take_hit(self)
     -- Haha, armor!
     self.health = self.health - 5
  end

  SuperVillain:new("Toht")

Coroutines

You may be wondering how Lua handles multithreading.

It doesn't.

Coroutines

Generator   B_example

  function fibonacci()
     local m = 1
     local n = 1

     while true do
        coroutine.yield(m)
        m, n = n, m + n
     end
  end

  generator = coroutine.create(fibonacci)
  succeeded, value = coroutine.resume(generator)
  -- value = 1

Multitasking

Example: Building a Scheduler

Excercises

Exercises

Day 3

Day 3: Lua and the World

Example: Making Music

Excercises

Exercises

Wrapping Up

Wrapping Up

A lot of programmers see the surface of Lua’s clean syntax and assume it’s just another everyday scripting language. I certainly had that feeling at first glance. But I hope that as you’ve taken a deeper look at its tables and coroutines, you’ve enjoyed their beauty and simplicity.

Wrapping Up: Strengths

• Approachable
• Portable
• Easily included in other projects

Wrapping Up: Weaknesses

• Batteries not included
• Inefficient string handling
• Quirky

Final Thoughts

Lua’s prototype-based object approach proves that you don’t need classes to build a great object system.