MonkeyScript

January 19, 2026 · View on GitHub

A lightweight, interpreted programming language written in C#. MonkeyScript features a simple syntax with support for functions, conditionals, loops, and basic arithmetic operations Note that this language has no future expectations, as this is just a "side quest" meant to sharpen my Computer Science knowledge and problem solving skills. If there is demand development will continue, but as it stands this project is concluded

Features

Dynamic typing with runtime type inference
First-class functions with closures
Lexical scoping with nested environments
Control flow with if/else and while loops
Function literals with parameter passing
REPL-ready architecture for interactive programming

Quick Start

Prerequisites

.NET 6.0 or higher
A C# IDE (Visual Studio, VS Code, or Rider recommended)

Running a Script

Create a file named script.ms:

def x = 5;
def y = 10;
def sum = x + y;
print(sum);

Run it:

dotnet run # or alternatively just use Visual Studio as I do

Language Syntax

Variables

def x = 42;
def name = myVariable;

Functions

def add = fn(a, b): a + b; end;
add(5, 3);

Conditionals

if x > 10:
    def result = 1;
else:
    def result = 0;
end;

Loops

def i = 0;
while i < 5:
    def i = i + 1;
end;

Expressions

def result = (10 + 5) - 3;
def isTrue = true;
def isFalse = false;

Architecture

MonkeyScript follows a classic interpreter architecture:

Lexical Analysis - The Lexer breaks source code into 'tokens'
Parsing - The Parser builds an Abstract Syntax Tree (AST)
Evaluation - The Evaluator walks the AST and executes code

Pipeline Flow

Source Code > Lexer > Tokens > Parser > AST > Evaluator > Eventual output

Examples

Factorial Function

def factorial = fn(n):
    if n < 2:
        1;
    else:
        n * factorial(n - 1);
    end;
end;

factorial(5);

Counter with Closure

def makeCounter = fn():
    def count = 0;
    fn():
        def count = count + 1;
        count;
    end;
end;

def counter = makeCounter();
counter();
counter();
counter();

Documentation

Language Specification - Complete language reference
Contributing Guide - How to contribute
Roadmap - Future features and plans

Contributing

Contributions are welcome! Please read CONTRIBUTING.md for details on our code of conduct and the process for submitting pull requests You're allowed to fork this and go on your own way but I'd like to contribute myself if demand is present (as I have the most knowledge about my own intepreter)