clojure.core/ensure-reduced

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Type: function Added: Clojure 1.7 Examples: 2 Runnable: 2

([x])

If x is already reduced?, returns it, else returns (reduced x)

Examples

by svenschoenung on 2016-05-26 ▶

(ensure-reduced :foo) ;;=> object[clojure.lang.Reduced 0x7dc19a70 {:status :ready, :val :foo}] (ensure-reduced (reduced :foo)) ;;=> object[clojure.lang.Reduced 0x45385f75 {:status :ready, :val :foo}]

by tomdl89 on 2023-04-23 ▶

;; If our reducing function's short-circuit coincides with our transducer's ;; short-circuit, `reduced` could lead to the reduction returning a Reduced: (defn conj-till-neg ([coll] coll) ([coll x] (cond-> (conj coll x) (neg? x) reduced))) (defn take-till-odd [rf] (fn new-rf ([result] (rf result)) ([result x] (cond-> (rf result x) (odd? x) reduced)))) (transduce take-till-odd conj-till-neg [] [6 4 2 -1 -2]) ;; => #<Reduced@5eee2f75: [6 4 2 -1]> ;; So we can change `reduced` to `ensure-reduced` to avoid doubling up: (defn take-till-odd [rf] (fn new-rf ([result] (rf result)) ([result x] (cond-> (rf result x) (odd? x) ensure-reduced)))) (transduce take-till-odd conj-till-neg [] [6 4 2 -1 -2]) ;; => [6 4 2 -1]

See also

• clojure.core/reduced (3)
• clojure.core/reduced?
• clojure.core/unreduced (1)
• clojure.core/reduce (22)

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