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Merged
heyLu merged 1 commit into from
Dec 24, 2015
Merged

add cycle #480

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13 changes: 13 additions & 0 deletions pixie/stdlib.pxi
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Original file line number Diff line number Diff line change
Expand Up @@ -1746,6 +1746,19 @@ The new value is thus `(apply f current-value-of-atom args)`."
s)))]
(lazy-seq (step pred coll)))))

(defn cycle
[coll]
(if (empty? coll)
()
(let [cycle'
(fn cycle' [current]
(lazy-seq
(cons
(first current)
(let [rst (rest current)]
(cycle' (if (empty? rst) coll rst))))))]
(cycle' coll))))

;; TODO: use a transient map in the future
(defn group-by
{:doc "Groups the collection into a map keyed by the result of applying f on each element. The value at each key is a vector of elements in order of appearance."
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6 changes: 6 additions & 0 deletions tests/pixie/tests/test-stdlib.pxi
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Expand Up @@ -568,6 +568,12 @@
(t/assert= (transduce (drop-while even?) conj [0 2] [1 4 6]) [0 2 1 4 6])
(t/assert= (transduce (drop-while even?) conj [0 2] [2 4 6 7 8]) [0 2 7 8]))

(t/deftest test-cycle
(t/assert= (cycle ()) ())
(t/assert= (cycle nil) ())
(t/assert= (take 5 (cycle '(1 2))) '(1 2 1 2 1))
(t/assert= (take 3 (cycle [nil])) '(nil nil nil)))

(t/deftest test-trace
(try
(/ 0 0)
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