Squirrel (programming language)

Squirrel is a high level imperative, object-oriented programming language, designed to be a light-weight scripting language that fits in the size, memory bandwidth, and real-time requirements of applications like video games and hardware such as Electric Imp.

MirthKit, a simple toolkit for making and distributing open source, cross-platform 2D games, uses Squirrel for its platform. It is used extensively by Code::Blocks for scripting and was also used in Final Fantasy Crystal Chronicles: My Life as a King It is also used in Left 4 Dead 2 and Portal 2 for scripted events.

Language features

• Dynamic typing
• Delegation
• Classes, inheritance
• Higher order functions
• Generators
• Cooperative threads (coroutines)
• Tail recursion
• Exception handling
• Automatic memory management (mainly reference counting with backup garbage collector)
• Weak references
• Both compiler and virtual machine fit together in about 7k lines of C++ code
• Optional 16-bit character strings

Syntax

Squirrel uses a C-like syntax.

Factorial in Squirrel

  function factorial(x)
  {
    if (x == 0) {
      return 1;
    }
    else {
      return x * factorial(x-1);
    }
  }

Generators

  function not_a_random_number_generator(max) {
    local last = 42;
    local IM = 139968;
    local IA = 3877;
    local IC = 29573;
    for(;;) { // loops forever
      yield (max * (last = (last * IA + IC) % IM) / IM);
    }
  }

  local randtor = not_a_random_number_generator(100);

  for(local i = 0; i < 10; i += 1)
     print(">"+resume randtor+"\n");

Classes and inheritance

  class BaseVector {
    constructor(...)
    {
      if(vargv.len() >= 3) {
        x = vargv[0];
        y = vargv[1];
        z = vargv[2];
      }
    }
    x = 0;
    y = 0;
    z = 0;
  }

  class Vector3 extends BaseVector {
    function _add(other)
    {
      if(other instanceof ::Vector3)
        return ::Vector3(x+other.x,y+other.y,z+other.z);
      else
        throw "wrong parameter";
    }
    function Print()
    {
      ::print(x+","+y+","+z+"\n");
    }
  }

  local v0 = Vector3(1,2,3)
  local v1 = Vector3(11,12,13)
  local v2 = v0 + v1;
  v2.Print();

Applications

Non-game applications using Squirrel

• Electric Imp

Games using Squirrel

• Vice City Multiplayer (a mod for Grand Theft Auto: Vice City)
• Left 4 Dead 2
• Portal 2
• Alien Swarm
• OpenTTD
• V-Multiplayer
• GTAIV's IV-MP
• Mafia II's M2-Multiplayer
• Counter Strike: Global Offensive
• Shadow Warrior
• War Thunder
• SuperTux
• Liberty Unleashed (a mod for Grand Theft Auto III)
• Sonic Unleashed (PS2/Wii)
• Contagion (PC)
• Thimbleweed Park
• Simutrans

History

The language was made public in 2003 under the zlib/libpng license. In November 2010, the license was changed to MIT license to enable the project to be hosted on Google Code. It is developed and maintained by Alberto Demichelis.

See also

• Lua
• Python
• ECMAScript
• Ruby

External links

• Squirrel Home Page
• SquirrelWiki
• Squirrel Documentation Project (Searchable)
• MirthKit Home Page
• L4D2 Vscripts
• SquiLu Squirrel modified with lua libraries