Squirrel

Paradigm	Multi-paradigm: scripting, imperative, functional, object-oriented
Designed by	Alberto Demichelis
First appeared	September 6, 2003; 20 years ago (2003-09-06)
Stable release	3.2[1]  / 10 February 2022; 23 months ago (10 February 2022)
Typing discipline	Dynamic
OS	Cross-platform
License	MIT license
Filename extensions	.nut
Website	squirrel-lang.org
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.^[2] It is used extensively by Code::Blocks for scripting and was also used in Final Fantasy Crystal Chronicles: My Life as a King.^[3][4] 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.^[5]

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::Blocks, integrated development environment
• Enduro/X, cluster application server
• Electric Imp, an end-to-end IoT platform^[6]

Games using Squirrel

History

The language was made public in 2003 under the zlib/libpng license.^[20] In November 2010, the license was changed to the MIT license to enable the project to be hosted on Google Code.^[21][22] It is developed and maintained by Alberto Demichelis.