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The Cub Programming Language

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version 1.0.1 Carthage Compatible Swift Platform: iOS macOS tvOS watchOS Extension: .cub
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Cub is an interpreted, dynamically typed, scripting language inspired by Swift. This project includes a lexer, parser, compiler and interpreter, all written in Swift.

Cub is used for OpenTerm's scripting feature. A language guide is available in OpenTerm and online. Cub was derived from Lioness (my first programming language).

The standard library (abbreviated: stdlib) contains basic utility functions, for example to convert from/to dates.

Source examples

The following Cub code calculates factorials recursively:

func factorial(x) returns {
    if x > 1 {
        return x * factorial(x - 1)
    return 1

a = factorial(5) // a = 120

The following Cub code uses a do times loop:

a = 1
n = 10
do n times {
    a += a
// a = 1024

More examples can be found here.

External functions

An important feature Cub has is the ability to define external functions. These functions are implemented in native code (for example Swift) and thus allows Cub to call native code.

An external function pauses the interpreter, executes the native code, and resumes the interpreter when the native code is executed.

The following example implements a print function:

let runner = Runner(logDebug: true, logTime: true)
runner.registerExternalFunction(name: "print", argumentNames: ["input"], returns: true) { (arguments, callback) in
	for (name, arg) in arguments {

External functions are called like any other global functions in Cub, the print function from the example above could be called like this:

print("Hello world")


  • Minimalistic, yet expressive, syntax
  • No type system, language is dynamic
  • 5 basic operators: +, -, /, * and ^
    • ^ means "to the power of", e.g. 2^10 equals 1024
    • all operators have a shorthand, e.g. += for +
  • Numbers
    • All numbers are floating point
  • Booleans
    • Can be evaluated from comparison
    • Can be defined by literal: true or false
  • Strings
    • Can be concatenated with the + operator
  • Arrays
    • Can contain any type, including other arrays
  • Functions
    • Supports parameters, returning and recursion
    • Can be declared inside other functions
  • Structs
    • Can contain any type, including other structs
  • Loops
    • for
    • while
    • do times
    • repeat while
    • break
    • continue
  • if / else / else if statements


Since the project does not rely on any dependencies, running it requires no setup.


Open Cub.xcworkspace (preferably in the latest non-beta version of Xcode) and run the macOS Example target. The example will run the code in A.cub. The output will be printed to the console.

Installing framework

Using Swift Package Manager

Add to your Package.swift file's dependencies section:

.Package(url: "https://github.com/louisdh/cub.git",
		         majorVersion: 1, minor: 0)

Using CocoaPods

Add the following line to your Podfile:

pod 'Cub', '~> 1.0'

Using Carthage

Add the following line to your Cartfile:

github "louisdh/cub" ~> 1.0

Run carthage update to build the framework and drag the built Cub.framework into your Xcode project.


  • [x] Structs
  • [x] Completion suggestions (given an incomplete source string and insertion point)
  • [ ] Breakpoint support in interpreter
  • [x] Stdlib documentation
  • [ ] Compiler warnings
  • [ ] Compiler optimizations
  • [x] Faster Lexer (without regex)
  • [x] Support emoticons for identifier names
  • [ ] guard statement
  • [ ] A lot more unit tests
  • [x] Linux support

Xcode file template

Cub source files can easily be created with Xcode, see XcodeTemplate.md for instructions.


A detailed explanation of the project's architecture can be found here.


This project is available under the MIT license. See the LICENSE file for more info.


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1.0.0 - May 17, 2018

Initial version included in OpenTerm 2.0.