@Meikal,
Hi, I get what you mean. Consider the following func -
(defn r
[n lazy?]
(.println System/out (str "Called (r " n ")"))
(let [r-lazy-seq (fn r-lazy-seq [i n]
(lazy-seq
(when (< i n)
(.println System/out (str "Realizing elem "
i))
(cons :a (r-lazy-seq (inc i) n)))))
zzz (r-lazy-seq 0 n)]
(if lazy? zzz (doall zzz))))
1:13 user=> (def k (for [a (r 2 true)] a) )
Called (r 2)
#'user/k
1:14 user=> (def k (for [a (r 2 false)] a) )
Called (r 2)
Realizing elem 0
Realizing elem 1
#'user/k
Why do you think for doesn't have 'lazy-for' semantics already?
Also this thread has given me the insight that 'for' is not meant for
Cartesian products of two seqs (contrary to what I thought) -
1:40 user=> (use '[clojure.contrib.combinatorics])
nil
1:41 user=> (cartesian-product (r 2 true) (r 3 true))
Called (r 2)
Called (r 3)
Realizing elem 0
Realizing elem 0
Realizing elem 1
Realizing elem 2
Realizing elem 1
((:a :a) (:a :a) (:a :a) (:a :a) (:a :a) (:a :a))
1:42 user=> (for [a (r 2 true) b (r 3 true)] [a b])
Called (r 2)
Realizing elem 0
Called (r 3)
Realizing elem 0
Realizing elem 1
Realizing elem 2
Realizing elem 1
Called (r 3)
Realizing elem 0
Realizing elem 1
Realizing elem 2
([:a :a] [:a :a] [:a :a] [:a :a] [:a :a] [:a :a])
- Thanks
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