var classyGreeting = (firstName, lastName) => "The name's " + lastName + ", " + firstName + " " + lastName; var yellGreeting = R.compose(R.toUpper, classyGreeting); yellGreeting("James", "Bond"); //=> "THE NAME'S BOND, JAMES BOND" R.compose(Math.abs, R.add(1), R.multiply(2))(-4); //=> 7 // get :: String -> Object -> Maybe * var get = R.curry((propName, obj) => Maybe(obj[propName])); // getStateCode :: Maybe String -> Maybe String var getStateCode = R.composeK( R.compose(Maybe.of, R.toUpper), get("state"), get("address"), get("user") ); getStateCode({ user: { address: { state: "ny" } } }); //=> Maybe.Just("NY") getStateCode({}); //=> Maybe.Nothing() var db = { users: { JOE: { name: "Joe", followers: ["STEVE", "SUZY"] } } }; // We'll pretend to do a db lookup which returns a promise var lookupUser = userId => Promise.resolve(db.users[userId]); var lookupFollowers = user => Promise.resolve(user.followers); lookupUser("JOE").then(lookupFollowers); // followersForUser :: String -> Promise [UserId] var followersForUser = R.composeP(lookupFollowers, lookupUser); followersForUser("JOE").then(followers => console.log("Followers:", followers)); // Followers: ["STEVE","SUZY"] const mapStateToProps = state => ({ users: R.compose( R.filter(R.propEq('status', 'active')), R.values)(state.users) });