ivenmarquardt

// Lazy Getters

/* What enables Tail Recursion Modulo Cons in Javascript is a thunk in Weak Head Normal Form.
   An expression in weak head normal form has been evaluated to the outermost data constructor,
   but contains sub-expressions that may not have been fully evaluated. In Javascript only thunks
   can prevent sub-expressions from being immediately evaluated. */

const cons = (head, tail) => ({head, tail});

sebmarkbage

let cache = new Map();
let pending = new Map();

function fetchTextSync(url) {
  if (cache.has(url)) {
    return cache.get(url);
  }
  if (pending.has(url)) {
    throw pending.get(url);
  }