Code golfing map/reduce/filter

hof-golfed.js

//----------------------------------------------------------------------------
// recursive golfed reduce
//----------------------------------------------------------------------------
let r = (f, a, [h, ...t]) => !t.length ? f(a, h) : r(f, f(a, h), t)
function reduce(fn, acc, [x, ...xs]) {
  return !xs.length
    ? fn(acc, x)
    : reduce(fn, fn(acc, x), xs);
}

//----------------------------------------------------------------------------
// recursive golfed map
//----------------------------------------------------------------------------
let m = (f, [h, ...t]) => !t.length ? [f(h)] : [f(h), ...m(f, t)]
function map(fn, [x, ...xs]) {
  return !xs.length
    ? [fn(x)]
    : [fn(x), ...map(fn, xs)]
}

//----------------------------------------------------------------------------
// recursive golfed map built using reduce
//----------------------------------------------------------------------------
let m2 = (f, xs) => r((ys, y) => [...ys, f(y)], [], xs);
function map_from_reduce(fn, xs) {
  let reduce_fn = (results, x) => [...results, fn(x)];
  return reduce(reduce_fn, [], xs);
}

//----------------------------------------------------------------------------
// recursive golfed filter
//----------------------------------------------------------------------------
let f = (p, [h, ...t]) => !t.length ? p(h) ? [h] : [] : p(h) ? [h, ...f(p, t)] : f(p, t)
function filter(fn, [x, ...xs]) {
  return !xs.length
    ? fn(x) ? [x] : []
    : fn(x) ? [x, ...filter(fn, xs)] : filter(fn, xs);
}

//----------------------------------------------------------------------------
// recursive golfed filter built using reduce
//----------------------------------------------------------------------------
let f2 = (p, xs) => r((ys, y) => p(y) ? [...ys, y] : ys, [], xs)
function filter_from_reduce(fn, xs) {
  let reduce_fn = (results, x) => fn(x) ? [...results, x] : results
  return reduce(reduce_fn, [], xs);
}