On Thu, Apr 4, 2013 at 8:44 AM, Tassilo Horn <t...@gnu.org> wrote:
>
> However, the what's bad with the juxt approach above is that the
> collection is iterated twice. If somebody comes up with a version that
> returns a vector of two lazy seqs and which iterates the input
> collection only once, she'd get my warmest thank you, and my vote for
> putting it into core.
>
>
here's a first shot, kind of ugly but seems to work:
user> (defn seqmr
[f g a bs]
(lazy-seq
(if (seq bs)
(g (f (first bs)) (seqmr f g a (rest bs)))
a)))
#'user/seqmr
user> (defn lazy-partition [p xs]
(seqmr (fn [x]
[(p x) x])
(fn [[t? x] r]
(if t?
[(lazy-seq (cons x (first r))) (lazy-seq (second r))]
[(lazy-seq (first r)) (lazy-seq (cons x (second r)))]))
[() ()]
xs))
#'user/lazy-partition
user> (def r (lazy-partition even? (map #(do (print % "") %) (range 129))))
#'user/r
user> (first (first r))
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
28 29 30 31
0
user> (first (second r))
1
user> (nth (second r) 10)
21
user> (nth (second r) 20)
32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56
57 58 59 60 61 62 63
41
user> (nth (first r) 20)
40
--
Ben Wolfson
"Human kind has used its intelligence to vary the flavour of drinks, which
may be sweet, aromatic, fermented or spirit-based. ... Family and social
life also offer numerous other occasions to consume drinks for pleasure."
[Larousse, "Drink" entry]
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