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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, released in September 6, 2003.

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, Team Fortress 2, Thimbleweed Park, and War Thunder 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]

• 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 support for UCS-2 wide strings

Version 2.0 was released in April 3, 2005.

The current Stable release is 3.2 in February 10, 2022.^[6]

The project has been designed to compile and run on Windows (86x, 64x), Linux, Illumos (both x86 & x64), and Android And, IOS, Mac Os And FreeBSD.^[7]

Has been tested with The Following Compilers:

• MS Visual C++ 6.0,7.0,7.1,8.0,9.0 and 10.0(x86 & x64)
• MinGW gcc 3.2 (mingw special 20020817-1)
• Cygwin gcc 3.2
• Linux gcc 3.x
• Linux gcc
• xIllumos
• xXCode 4

While Squirrel is a dynamically typed language and variables do not have a type, different operations may interpret the variable as containing a type. Squirrel’s basic types are integer, float, string, null, table, array, function, generator, class, instance, bool, thread and userdata.^[8]

An Integer represents a 32 bit (or better) signed number.:^[9]

local a = 123 //decimal
local b = 0x0012 //hexadecimal
local c = 075 //octal [10]

A float represents a 32 bit (or better) floating point number.:

local a=1.0 local b=0.234

strings are an immutable sequence of characters. In order to modify a string is it necessary create a new one.^[11]

Squirrel’s strings are similar to strings in C or C++. They are delimited by quotation marks(") and can contain escape sequences (\t, \a, \b, \n, \r, \v, \f, \\, \", \', \0, \x<hh>, \u<hhhh> and \U<hhhhhhhh>).

Verbatim string literals do not interpret escape sequences. They begin with @" and end with the matching quote. Verbatim string literals also can extend over a line break. If they do, they include any white space characters between the quotes:

local a = "I'm a wonderful string\n"
// has a newline at the end of the string
local x = @"I'm a verbatim string\n"
// the \n is literal, similar to "\\n" in a regular string.

However, a doubled quotation mark within a verbatim string is replaced by a single quotation mark:^[6]

local multiline = @"
    this is a multiline string
    it will ""embed"" all the new line
    characters 

The null value is a primitive value that represents the null, empty, or non-existent reference. The type Null has exactly one value, called null.:

local a = null

Bool is a double-valued (Boolean) data type. Its literals are true and false. A bool value expresses the validity of a condition (tells whether the condition is true or false).:^[12]

local a = true;

Tables are associative containers implemented as a set of key/value pairs called slots.:

local t={}
local test=
{
    a=10
    b=function(a) { return a+1; }
}

Arrays are simple sequence of objects. Their size is dynamic and their index always starts from 0.:^[13]

local a  = ["I'm","an","array"]
local b = [null]
b[0] = a[2];

Functions are similar to those in other C-like languages with a few key differences (see below).

Classes are associative containers implemented as sets of key/value pairs. Classes are created through a ‘class expression’ or a ‘class statement’. class members can be inherited from another class object at creation time. After creation, members can be added until an instance of the class is created.^[14]

Class instances are created by calling a class object. Instances, as tables, are implemented as sets of key/value pairs. Instance members cannot be dynamically added or removed; however the value of the members can be changed.^[15]

Generators are functions that can be suspended with the statement ‘yield’ and resumed later (see Generators).^[13]

Userdata objects are blobs of memory or pointers defined by the host application but stored within Squirrel variables (See Userdata and UserPointers).

Threads are objects representing a cooperative thread of execution, also known as coroutines.

Weak References are objects that point to another (non-scalar) object but do not own a strong reference to it. (See Weak References).^[12]

The following words are reserved and cannot be used as identifiers:^[12]

Identifiers start with an alphabetic character or the symbol ‘_’ followed by any number of alphabetic characters, ‘_’ or digits ([0-9]). Squirrel is a case sensitive language meaning that the lowercase and uppercase representation of the same alphabetic character are considered different characters. For instance, “foo”, “Foo” and “fOo” are treated as 3 distinct identifiers.^[12]

Squirrel recognizes the following operators:

As for Significant tokens:

A comment is text that the compiler ignores but that is useful for programmers. Comments are normally used to embed annotations in the code. The compiler treats them as white space.^[12]

A comment can be /* (slash, asterisk) characters, followed by any sequence of characters (including new lines), followed by the */ characters. This syntax is the same as ANSI C:^[12]

/* any text between will be ignored */

Squirrel accepts integer numbers, floating point numbers and string literals.

squirrel’s syntax is similar to C/C++/Java etc… but the language has a very dynamic nature like Python/Lua etc…^[12]

local function factorial(x) // Getting function which is factorial, then getting value which is x
{
  if (x <= 1) {  // if x is less than 1
    return 1;  // then the code will just return 1
  }
  else { // if that doesn't work
    return x * factorial(x-1); // then the code will return x times factorial(x-1)
  }
}

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");

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();

• Code::Blocks, integrated development environment
• Enduro/X, cluster application server
• Electric Imp, an end-to-end IoT platform^[16]

The language was made public in 2003 under the zlib/libpng license.^[34] In November 2010, the license was changed to the MIT license to enable the project to be hosted on Google Code.^[35][36] It is developed and maintained by Alberto Demichelis.

• Lua
• AngelScript
• Python
• ECMAScript
• Ruby

• Official website
• Squirrel docment