The `reduced?` check is there in case somebody returns a `reduced` as
acc value from the reducing function, as a way to terminate the
reduction early:
user=> (reductions (fn [_ x] (if (= 10 x) (reduced x) x)) (range))
(0 1 2 3 4 5 6 7 8 9 10)
deref is the way to retrieve the value of a reduced object:
user=> (deref (reduced 1))
1
Alex Eberts writes:
> Hi All,
>
> Could someone please explain why reduced? is being used in the reductions
> function (below)? From what I understand reduced? checks if there has been
> a call to reduced and I don't see where that might be happening.
>
> Also, why is the deref macro being used with init?
>
> thanks,
> Alex
>
>
> (defn reductions
> "Returns a lazy seq of the intermediate values of the reduction (as
> per reduce) of coll by f, starting with init."
> {:added "1.2"}
> ([f coll]
> (lazy-seq
> (if-let [s (seq coll)]
> (reductions f (first s) (rest s))
> (list (f)))))
> ([f init coll]
> (if (reduced? init)
> (list @init)
> (cons init
> (lazy-seq
> (when-let [s (seq coll)]
> (reductions f (f init (first s)) (rest s))))))))
>
> from:
> https://github.com/clojure/clojure/blob/clojure-1.7.0/src/clj/clojure/core.clj#L6921
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