how to add functions on can.Map

How do I add a function to a can.Map? This is what I tried, but it's undefined. I expected a function.

var M = can.Map.extend({
            first: "largo",
            last: "elks",
            speak: function () {
                alert("you nailed it");
            }
        });
var m = new M({})
console.log(m.attr("speak")); // undefined