Question

I have a list, which may contain elements that will compare as equal. I would like a similar list, but with one element removed. So from (:a :b :c :b :d) I would like to be able to “remove” just one :b to get (:a :c :b :d).

The context is a hand in a card game where two decks of standard cards are in play, so there may be duplicate cards but still played one at a time.

I have working code, see below. Are there more idiomatic ways to do this in Clojure?

(defn remove-one [c left right]
  (if (= right ())
    left
    (if (= c (first right))
      (concat (reverse left) (rest right))
      (remove-one c (cons (first right) left) (rest right)))))

(defn remove-card [c cards]
  (remove-one c () cards))

Here are the Scala answers I got a while ago: What is an idiomatic Scala way to "remove" one element from an immutable List?

Answer 1

How about:

(let [[n m] (split-with (partial not= :b) [:a :b :c :b :d])] (concat n (rest m)))

Which splits the list at :b and then removes the :b and concats the two lists.