An Interpreter Written in Go

It is a simple interpreter written in Go, named Monkey.
It was built as a way to learn how interpreted languages are implemented.

Overview

Monkey is a dynamically typed, interpreted language with a C-like syntax. It supports variable bindings, integers, booleans, arithmetic expressions, built-in functions, first-class and higher-order functions, closures, strings, arrays, and hashes.

Language Syntax

Variables

let age = 25;
let name = "John";

Arithmetic Expressions

let sum = 5 + 5;
let product = 5 * 5;
let quotient = 10 / 2;
let difference = 10 - 5;

Boolean Expressions

let isAdult = age > 18;
let isEqual = (10 == 10);
let isNotEqual = (10 != 9);

Functions

let add = fn(x, y) { x + y };
let result = add(5, 10);

Strings

let greeting = "Hello, " + name + "!";

Arrays

let numbers = [1, 2, 3, 4, 5];
let firstNumber = numbers[0];

Hashes

let person = {"name": "John", "age": 25};
let personName = person["name"];

Example Programs

Hello World

puts("Hello, World!");

Map Function

let map = fn(arr, f) {
    let iter = fn(arr, accumulated) {
        if (len(arr) == 0) {
            accumulated
        } else {
            iter(rest(arr), push(accumulated, f(first(arr))));
        }
    };

    iter(arr, []);
};

let double = fn(x) { x * 2 };
let result = map([1, 2, 3, 4], double);
puts(result); // [2, 4, 6, 8]

Factorial

let factorial = fn(n) {
    if (n == 0) {
        1
    } else {
        n * factorial(n - 1);
    }
};

puts(factorial(5)); // 120

Fibonacci

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

puts(fibonacci(10)); // 55

Built-in Functions

len

Returns the length of a string or array.

len("hello"); // 5
len([1, 2, 3]); // 3

first

Returns the first element of an array.

first([1, 2, 3]); // 1

last

Returns the last element of an array.

last([1, 2, 3]); // 3

rest

Returns the array without the first element.

rest([1, 2, 3]); // [2, 3]

push

Adds an element to the end of an array.

push([1, 2, 3], 4); // [1, 2, 3, 4]

How to Use

To run it, you'll need Git and Go installed on your computer. From your command line:

# Clone this repository
$ git clone https://github.com/ekastn/monkey

# Go into the repository
$ cd monkey

# Build the project
$ go build -o bin/monkey cmd/main.go

# Run the REPL
$ ./bin/monkey