ideas.jls

reduce = [init, arr, combine] => match(arr) {
  [head, tail...] => (
    reduce([combine([init, head]), tail, combine])
  );

  [] => (
    init
  );
};

sum = (arr) => (
  reduce(0, arr, [a, b] => a + b);
);

sum = (arr) => {
  res = 0;

  arr.each(x => res += x);

  return res;
};

reduce = [v, arr, combine] => {
  arr.each(x => v = combine(v, x));
  return init;
};

each = [arr, fn] => {
  match(arr) {
    [head, tail...] => {
      fn(head);
      each(tail, fn);
    };

    [] => ();
  };
};

map = (() => {
  impl = [curr, rem, fn] => match(rem) {
    [head, tail...] => impl[[curr..., head], tail, fn];
  };

  return [arr, fn] => impl[[], arr, fn];
})();

qMap = [curr = [], arr, fn] => match(arr) {
  [head, tail...] => qMap[[curr..., fn(head)], tail, fn];
};

mapImpl = [curr, rem, fn] => match(rem) {
  [head, tail...] => mapImpl[[curr..., fn(head)], tail, fn];
  []              => [];
};

map = [arr, fn] => mapImpl([[], arr, fn]);

lazyMap = [arr, fn] => match(arr) {
  [] => [];
  [head, tail...] => [fn(head), lazyMap[tail, fn]...];
};

map = [arr, fn] => match(arr) {
  [head, tail...] => (
    [fn(head), map[tail, fn]...];
  );

  [] => [];
};

sum = arr => match(arr) {
  [head, tail...] => head + sum(tail);
  [] => 0;
};

reduce = [acc, arr, join] => match(arr) {
  [head, tail...] => reduce[join[acc, head], arr, join]];
  [] => acc;
};

arrToList = (() => {
  impl = [list, arr] => match(arr) {
    [] => list;
    [head..., tail] => impl[{value: tail, next: list}, head];
  };

  return arr => impl[(), arr];
})();

sum = (() => {
  impl = [s, arr] => match(arr) {
    [] => s;
    [head, tail...] => impl[s + head, tail];
  };

  return arr => impl[0, arr];
})();

arrToList = arr => revReduce[(), arr, [list, x] => {value: x, next: list}];

listReduce = [acc, list, join] => match(list) {
  () => acc;
  {value, next} => listReduce[join[acc, value], next, join];
};

match(getAnswer()) {
  'yes' => console.log('You said yes.');
  'no'  => console.log('boo');
};

if ([a, b] matches values) {
  console.log('Got two values', a, b);
}