Ar.js

var Ar = {
  filter: function(fn, list) {
    if (!list[0]) return [];
    if (fn(list[0])) return [list[0]].concat(Ar.filter(fn, list.slice(1)));
    return [].concat(Ar.filter(fn, list.slice(1)));
  },
  first: function(fn, list) {
    if (!list[0]) return null;
    if (fn(list[0])) return list[0];
    return Ar.first(fn, list.slice(1));
  },
  map: function (fn, list) {
    if (!list[0]) return [];
    return [fn(list[0])].concat(Ar.map(fn, list.slice(1)));
  }
};
var numbers = [ 1,2,3 ];

function isEven(x) {
  return x % 2 === 0;
}
document.write('<br>filter: ' + Ar.filter(isEven, numbers));

function square(x) {
  return x * x;  
}
document.write('<br>map^2: ' + Ar.map(square, numbers));

function greaterThan2(x) {
  return x > 2;
}
document.write('<br>first: ' + Ar.first(greaterThan2, numbers));

Partial.js

function Partial(fn /*, args...*/) {
  var slice = Array.prototype.slice;
  var args = slice.call(arguments, 1);
  return function() {
    return fn.apply(this, args.concat(slice.call(arguments, 0)));
  };
}

var squareList = Partial(Ar.map, square);
document.write('<br>map^2: ' + squareList(numbers));