flatMap.js

var Observ = require('observ');

/* flatMap := (Observ<T>, (T) => Observ<S>) => Observ<S>

*/
function flatMap(observ, fn) {
    var v = fn(observ());

    var result = Observ(v());
    v(result.set);

    observ(function (t) {
        v = fn(t);
        result.set(v());
        v(result.set);
    });

    return result
}