Show HN: Matches.js -- Powerful Pattern Matching for Javascript(github.com)

    var env = λ.environment()
        .method('length', λ.isArray, function(a) {
            return a.length;
        })
        .method('length', λ.isString, function(s) {
            return s.length;
        })
        .property('empty', function(o) {
            return !this.length(o);
        });

    env.empty([]) == true;
    env.empty([1, 2, 3]) == false;

  mymap = pattern {
    '_, []' : -> []
    'f, [x, xs...]' : (f, x, xs) -> 
      [f x].concat mymap(f, xs)
  }