Elm Monkey Interpreter (Playground)

A Monkey interpreter written in Elm.

Monkey is a programming language designed by Thorsten Ball that is fully described in his interpreter book.

Syntax

The syntax of Monkey is scattered throughout the pages of the book. However, I extracted a context-free grammar that you can use to learn the syntax.

let filter = fn (pred, arr) {
  let iter = fn (arr, accumulated) {
    if (len(arr) == 0) {
      accumulated
    } else {
      if (pred(first(arr))) {
        iter(rest(arr), push(accumulated, first(arr)))
      } else {
        iter(rest(arr), accumulated)
      }
    }
  };
  iter(arr, [])
};

let mod = fn (a, b) {
  a - a / b * b
};

let isEven = fn (n) {
  mod(n, 2) == 0
};

filter(isEven, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

You can also use the parser tests as a guide.

Semantics

The semantics is defined by the interpreter. You can get a sense for it by reading through the extensive suite of interpreter tests.