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.^[1] It is used extensively by Code::Blocks for scripting and was also used in Final Fantasy Crystal Chronicles: My Life as a King^[2][3] It is also used in Left 4 Dead 2 and Portal 2 for scripted events.^[4]

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)^[5]
• Left 4 Dead 2^[6]
• Portal 2^[6]
• Alien Swarm^[6]
• OpenTTD^[7]
• V-Multiplayer^[8]
• GTAIV's IV-MP^[9]
• Mafia II's M2-Multiplayer^[10]
• Counter Strike: Global Offensive^[6]
• Shadow Warrior
• War Thunder
• SuperTux
• Liberty Unleashed (a mod for Grand Theft Auto III)
• Sonic Unleashed (PS2/Wii)
• Contagion^[6] (PC)
• Thimbleweed Park^[11]
• Simutrans^[12]

History

The language was made public in 2003 under the zlib/libpng license.^[13] In November 2010, the license was changed to MIT license to enable the project to be hosted on Google Code.^[14][15] It is developed and maintained by Alberto Demichelis.

See also

• Lua
• Python
• ECMAScript
• Ruby

References

1. ↑ MirthKit Developer Wiki
2. ↑ Brandon Boyer (21 February 2008). "Gamasutra - GDC 2008 Event Coverage". gamasutra.com. Gamasutra. 
3. ↑ "Exclusive: Behind The Scenes of Final Fantasy's WiiWare Debut". gamasutra.com. Gamasutra. 23 June 2008. Retrieved 22 September 2011. 
4. ↑ L4D2 Vscripts
5. ↑ "Welcome to Vice City Multiplayer website!". vicecitymultiplayer.com. Retrieved 2014-05-04. 
6. 1 2 3 4 5 "VScript". valvesoftware.com. 2014-08-20. Retrieved 2015-01-17. 
7. ↑ http://wiki.openttd.org/?title=AI:Main_Page&oldid=76593
8. ↑ http://www.5-mp.com/index
9. ↑ http://www.iv-multiplayer.com
10. ↑ http://www.m2-multiplayer.com
11. ↑ http://blog.thimbleweedpark.com/engine
12. ↑ http://dwachs.github.io/simutrans-sqapi-doc/
13. ↑ "The Squirrel programming language". sourceforge.net. Retrieved 25 September 2011. 
14. ↑ "Moving to code.google.com and MIT License". squirrel-lang.org. Retrieved 25 September 2011. 
15. ↑ "squirrel". google.com. Retrieved 25 September 2011. 

External links

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