Assoc list value search by key, inspired with Haskell language style

haskellStyleAssocListValueByKeyFind.js

const Nothing = Symbol('Nothing');
const Just = (value) => Symbol("Just " + JSON.stringify(value));

const isAssocList = (value) => {
  return Array.isArray(value) && value.length === 2;
};

const findAssocListValueByKey = (list, key) => {
  const [assocItem, ...items] = list;
  if (undefined === assocItem) {
    return Nothing;
  }
  const [assocKey, assocVal] = assocItem;
  if (assocKey === key && !isAssocList(assocVal)) {
    return Just(assocVal);
  } else if (isAssocList(assocVal)) {
    return findAssocListValueByKey([...assocVal, ...items], key);
  } else {
    return findAssocListValueByKey(items, key);
  }
};

Usage:

const input = [
  ["a", 1],
  ["b", 2],
  ["c", [
    ["d", 4],
    ["e", [
      ["f", 6],
      ["g", 7]
    ]]
  ]]
];

const output = findAssocListValueByKey(input, "f");
console.log(output); // gives: Symbol(Just 6)