Is this code applying an amount due against a customer's list of credit
cards? If so, there seems to be a bug. The third line should be:
card.appliedBalance = min(due, card.balance)
and the Clojure code I'd write is:
(defrecord Card [balance applied-balance])
(defn apply-due-to-cards [[due new-cards] card]
(let [applied-bal (min due (:balance card))]
[(- due applied-bal)
(conj new-cards (->Card (:balance card) applied-bal))]))
(assert (=
(reduce apply-due-to-cards [100 []]
[(->Card 10 0) (->Card 30 0) (->Card 150 0)])
[0
[(->Card 10 10) (->Card 30 30) (->Card 150 60)]]))
Also four lines long like the Ruby example, but it's easier to debug when
there's a bug just by changing `reduce` to `reductions`. It's also
threadsafe, and can be parallelized for large datasets by using the Clojure
5 Reducers library.
On Friday, May 3, 2013 5:21:46 AM UTC+8, Steven Degutis wrote:
>
> Given pseudo-code (Ruby-ish):
>
> due = 100
> cards = cards.map do |card|
> card.applied_balance = max(0, due - card.balance)
> due -= card.applied_balance
>
> Notice how due changes at each turn, and each successive item in
> "cards" sees the change.
>
> What's an idiomatic way to do this in Clojure without using refs?
>
> -Steven
>
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