Squirrel (programming language)

Short description: Computer programming language

Squirrel

Paradigm	Multi-paradigm: scripting, imperative, functional, object-oriented
Designed by	Alberto Demichelis
First appeared	September 6, 2003 (2003-09-06)
Typing discipline	Dynamic
OS	Cross-platform
License	MIT license
Filename extensions	.nut
Website	{{{1}}}
Influenced by
C++, JavaScript, Lua, Python
Influenced
MiniD

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

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 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, Portal 2 and Thimbleweed Park for scripted events and in NewDark, an unofficial Thief 2: The Metal Age engine update, to facilitate additional, simplified means of scripting mission events, aside of the regular C scripting.

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 <= 1) {
    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

Applications using Squirrel

• Code, integrated development environment
• Enduro/X, cluster application server
• Electric Imp, an end-to-end IoT platform

Games using Squirrel

• Alien Swarm
• Antinomy of Common Flowers
• Apex Legends
• Battle Brothers
• Contagion
• Counter Strike: Global Offensive
• CRSED
• Final Fantasy Crystal Chronicles: My Life as a King
• GTA IV's IV-MP
• Left 4 Dead 2
• Liberty Unleashed
• Mafia II's M2-Multiplayer
• Nuclear Dawn
• OpenTTD
• Portal 2
• Shadow Warrior
• Simutrans
• Sonic Unleashed (PS2/Wii)
• SuperTux
• Team Fortress 2
• Thimbleweed Park
• Thief II (unofficial NewDark engine update)
• Titanfall
• Vice City Multiplayer, a mod for Grand Theft Auto
• War Thunder
• Zero no Tsukaima - Maigo no Period to Ikusen no Symphony (PS2)
• Zero no Tsukaima - Muma ga Tsumugu Yokaze no Nocturne (PS2)
• Zero no Tsukaima - Shou-akuma to Harukaze no Concerto (PS2)

History

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

See also

• Lua
• AngelScript
• Python
• ECMAScript
• Ruby