Javascript port of https://gist.github.com/kaaloo/6884209

gistfile1.js

var Zero = {
  isZero: function() {
    return true;    
  },
    
  predecessor: function() {
    throw "No such element";
  },
    
  successor: function() {
    return new Succ(this);
  },
    
  add: function(that) {
    return that;
  },
    
  sub: function(that) {
    if (that.isZero()) {
      return this;
    } else {
      return predecessor().sub(that.predecessor())
    }
  }
};

function Succ(n) {
    this.n = n;
}

Succ.prototype.isZero = function() {
    return false;
}

Succ.prototype.predecessor = function() {
    return this.n;
}

Succ.prototype.successor = function() {
    return new Succ(this);
}

Succ.prototype.add = function(that) {
    new Succ(n.add(that))
}

Succ.prototype.sub = function(that) {
  if (that.isZero()) {
    return this;
  } else {
    return predecessor().sub(that.predecessor())
  }    
}