Monkey Programming Language

A simple, dynamically typed scripting language with C-like syntax, inspired by the book "Writing An Interpreter In Go" by Thorsten Ball.

Features

• C-like syntax with minimal punctuation
• Dynamic typing
• First-class functions and closures
• Higher-order functions
• Built-in data types: integers, booleans, strings, arrays, hashes
• Simple REPL environment

Example Code

let x = 5;
let y = 10;
let name = "Monkey";
let isCool = true;
let array = [1, 2, 3, 4, 5];
let hash = {"name": "Monkey", "age": 5};

let add = fn(a, b) {
    return a + b;
};

let fibonacci = fn(n) {
    if (n == 0) { return 0; }
    if (n == 1) { return 1; }
    return fibonacci(n - 1) + fibonacci(n - 2);
};

puts("Fibonacci of 10 is:", fibonacci(10));

Getting Started

Prerequisites

• Go 1.13+ (for the reference implementation)

Installation

1. Clone the repository:

git clone https://github.com/Neel-shetty/monkey.git
cd monkey

2. Build the interpreter:

go build -o monkey .

Usage

REPL Mode:

./monkey

Run a script:

./monkey examples/hello.monkey

Language Reference

Data Types

• Integers: let x = 42;
• Booleans: let flag = true;
• Strings: let name = "Monkey";
• Arrays: let arr = [1, 2, 3];
• Hashes: let person = {"name": "Alice", "age": 30};

Control Structures

Conditionals:

if (x > y) {
    puts("x is greater");
} else {
    puts("y is greater or equal");
}

Functions

let greet = fn(name) {
    return "Hello " + name + "!";
};

let applyTwice = fn(f, x) {
    return f(f(x));
};

Built-in Functions

• puts(...): Print values to stdout
• len(x): Get length of string or array
• first(arr): Get first element of array
• rest(arr): Get all elements except first
• push(arr, val): Append value to array

Examples

See the examples/ directory for more code samples:

• array.monkey: Array operations and higher-order functions
• closure.monkey: Demonstrates closures
• hashmap.monkey: Hash map data structure usage
• hello.monkey: Simple hello world example
• math.monkey: Basic mathematical operations

Contributing

Contributions are welcome! Please open an issue or submit a pull request.

License

MIT License

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Monkey was created as part of the book "Writing An Interpreter In Go" by Thorsten Ball. This implementation is for educational purposes.