You can use reduce to carry forward both the new value on the cards, and
the new value of "due".
user> (let [due 100
cards [{:balance 120} {:balance 30} {:balance 35} {:balance
40}]]
(reduce (fn [[due cards] card]
(let [applied (max 0 (- due (:balance card)))]
[(- due applied) (conj cards (assoc card
:applied-balance applied))]))
[due []]
cards))
[30 [{:applied-balance 0, :balance 120} {:applied-balance 70, :balance 30}
{:applied-balance 0, :balance 35} {:applied-balance 0, :balance 40}]]
The first item in the result is the remaining balance, the second is
"mutated" cards.
On Thu, May 2, 2013 at 2:21 PM, Steven Degutis <[email protected]> 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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