class Person {
    func compose(getter: SignalProducer<StoreItem, StoreError>,
                 withNext next: SignalProducer<StoreItem, StoreError>,
                 cashInHand: Double) -> SignalProducer<StoreItem, StoreError> {
        return getter
            .flatMapError { _ in next }
            .flatMap(.latest) { item -> SignalProducer<StoreItem, StoreError> in
                if item.price <= cashInHand { return SignalProducer(value: item) }
                return next
            }
    }
}

class Ted: Person {
    func searchForFood(at store: Store, cashInHand: Double) -> SignalProducer<StoreItem, FoodSearchError> {
        var getter = store.getItem(named: "Ceasar Sallad")
        getter = compose(getter: getter, withNext: store.getItem(named: "Tomato and Basil soup"), cashInHand: cashInHand)
        getter = compose(getter: getter, withNext: store.getItem(named: "Lots of Peanuts"), cashInHand: cashInHand)

        return getter.mapError { _ in .willStarve }
    }
}