Returns a lazy sequence consisting of the result of applying f to 0
and the first item of coll, followed by applying f to 1 and the second
item in coll, etc, until coll is exhausted. Thus function f should
accept 2 arguments, index and item.
Source
clojure/core.clj:6312
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(defn map-indexed
"Returns a lazy sequence consisting of the result of applying f to 0
and the first item of coll, followed by applying f to 1 and the second
item in coll, etc, until coll is exhausted. Thus function f should
accept 2 arguments, index and item."
{:added "1.2"
:static true}
[f coll]
(letfn [(mapi [idx coll]
(lazy-seq
(when-let [s (seq coll)]
(if (chunked-seq? s)
(let [c (chunk-first s)
size (int (count c))
b (chunk-buffer size)]
(dotimes [i size]
(chunk-append b (f (+ idx i) (.nth c i))))
(chunk-cons (chunk b) (mapi (+ idx size) (chunk-rest s))))
(cons (f idx (first s)) (mapi (inc idx) (rest s)))))))]
(mapi 0 coll)))
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