Monkey RS

What's Monkey?

The official Monkey logo

Monkey is a programming language designed to learn interpreters.

It's came from Thorsten Ball's excellent book Writing An Interpreter in Go.

I create this repo mainly for learning the rust language.

Monkey Language

Monkey looks like this:

// Bind values to names with let-statements
let version = 1;
let name = "Monkey programming language";
let myArray = [1, 2, 3, 4, 5];
let coolBooleanLiteral = true;

// Use expressions to produce values
let awesomeValue = (10 / 2) * 5 + 30;
let arrayWithValues = [1 + 1, 2 * 2, 3];

Monkey supports builtin data structures: booleans, strings, hashes, integers and arrays.

// Here is an array containing two hashes, that use strings as keys and integers
// and strings as values
let people = [{"name": "Anna", "age": 24}, {"name": "Bob", "age": 99}];

// Getting elements out of the data types is also supported.
// Here is how we can access array elements by using index expressions:
fibonacci(myArray[4]);
// => 5

// We can also access hash elements with index expressions:
let getName = fn(person) { person["name"]; };

// And here we access array elements and call a function with the element as
// argument:
getName(people[0]); // => "Anna"
getName(people[1]); // => "Bob"

In monkey, functions are first-class citizens.

// Define the higher-order function `map`, that calls the given function `f`
// on each element in `arr` and returns an array of the produced values.
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, []);
};

// Now let's take the `people` array and the `getName` function from above and
// use them with `map`.
map(people, getName); // => ["Anna", "Bob"]

And, of course, Monkey also supports closures:

// newGreeter returns a new function, that greets a `name` with the given
// `greeting`.
let newGreeter = fn(greeting) {
  // `puts` is a built-in function we add to the interpreter
  return fn(name) { puts(greeting + " " + name); }
};

// `hello` is a greeter function that says "Hello"
let hello = newGreeter("Hello");

// Calling it outputs the greeting:
hello("dear, future Reader!"); // => Hello dear, future Reader!

So, to summarize: Monkey has a C-like syntax, supports variable bindings, prefix and infix operators, has first-class and higher-order functions, can handle closures with ease and has integers, booleans, arrays and hashes built-in.

How to Use

with REPL

$ git clone https://github.com/ijingo/monkey-rs
$ cargo run

Language Syntax Reference

Please refer to Writing An Interpreter in Go.

A non official document link.

License

Licensed under the MIT license.

ijingo / monkey-rs