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Implement drop-last

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This commit is contained in:
han semaj 2014-08-22 21:09:59 +12:00
parent 7e5befa615
commit 7f5c8e39d8
3 changed files with 46 additions and 2 deletions
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26
docs/language/core.rst
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@ -822,6 +822,32 @@ Raises ``ValueError`` if ``n`` is negative.
=> (list (drop 6 [1 2 3 4 5]))
[]
.. _drop-last-fn:
drop-last
---------
Usage: ``(drop-last n coll)``
Return an iterator of all but the last ``n`` items in ``coll``. Raise ``ValueError`` if ``n`` is negative.
.. code-block:: hy
=> (list (drop-last 5 (range 10 20)))
[10, 11, 12, 13, 14]
=> (list (drop-last 0 (range 5)))
[0, 1, 2, 3, 4]
=> (list (drop-last 100 (range 100)))
[]
=> (import itertools)
=> (list (take 5 (drop-last 100 (itertools.count 10))))
[10, 11, 12, 13, 14]
.. _drop-while-fn:
drop-while

9
hy/core/language.hy
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@ -57,7 +57,6 @@
(and (instance? (type :foo) k)
(.startswith k (get :foo 0))))
(defn dec [n]
"Decrement n by 1"
(_numeric-check n)
@ -119,6 +118,12 @@
"Drop `count` elements from `coll` and yield back the rest"
(itertools.islice coll count nil))
(defn drop-last [n coll]
"Return a sequence of all but the last n elements in coll."
(let [[iters (itertools.tee coll)]]
(map first (apply zip [(get iters 0)
(drop n (get iters 1))]))))
(defn empty? [coll]
"Return True if `coll` is empty"
(= 0 (len coll)))
@ -354,7 +359,7 @@
(def *exports* '[butlast calling-module-name coll? cons cons? cycle
dec distinct disassemble drop drop-while empty? even?
dec distinct disassemble drop drop-last drop-while empty? even?
every? first filter filterfalse flatten float? gensym identity
inc input instance? integer integer? integer-char? interleave
interpose iterable? iterate iterator? keyword? list*

13
tests/native_tests/core.hy
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@ -117,6 +117,19 @@
(setv res (list (take 5 (drop 2 (iterate inc 0)))))
(assert-equal res [2 3 4 5 6]))
(defn test-drop-last []
"NATIVE: testing drop-last function"
(assert-equal (list (drop-last 5 (range 10 20)))
[10 11 12 13 14])
(assert-equal (list (drop-last 0 (range 5)))
[0 1 2 3 4])
(assert-equal (list (drop-last 100 (range 100)))
[])
; with an infinite sequence
(import itertools)
(assert-equal (list (take 5 (drop-last 100 (itertools.count 10))))
[10 11 12 13 14]))
(defn test-drop-while []
"NATIVE: testing drop-while function"
(setv res (list (drop-while even? [2 4 7 8 9])))