Expands to code which yields a lazy sequence of the concatenation
of the supplied colls. Each coll expr is not evaluated until it is
needed.
(lazy-cat xs ys zs) === (concat (lazy-seq xs) (lazy-seq ys) (lazy-seq zs))
;; N.B. this example holds onto the head of a lazy seq which should generally be avoided
(def fib-seq
(lazy-cat [0 1] (map + (rest fib-seq) fib-seq)))
(take 10 fib-seq)
;; When the producer function produces a collection, not an element, ;; lazy-cat is usable. user=> (defn n-repeat [n] (lazy-cat (repeat n n) (n-repeat (inc n)))) #'user/n-repeat user=> (take 6 (n-repeat 1)) (1 2 2 3 3 3) user=> (take 12 (n-repeat 1)) (1 2 2 3 3 3 4 4 4 4 5 5)
Source
clojure/core.clj:3572
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(defmacro lazy-cat
"Expands to code which yields a lazy sequence of the concatenation
of the supplied colls. Each coll expr is not evaluated until it is
needed.
(lazy-cat xs ys zs) === (concat (lazy-seq xs) (lazy-seq ys) (lazy-seq zs))"
{:added "1.0"}
[& colls]
`(concat ~@(map #(list `lazy-seq %) colls)))
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