branch: externals/dash
commit dd30a1fbbae0201cfd0b861e3150ba6ea5d500fd
Author: holomorph <mvote...@udel.edu>
Commit: Matus Goljer <dota.k...@gmail.com>
[Feature #196] Add -powerset and -permutations (#203)
---
dash.el | 16 ++++++++++++++++
dev/examples.el | 9 +++++++++
2 files changed, 25 insertions(+)
diff --git a/dash.el b/dash.el
index 27dd2c1..a094e41 100644
--- a/dash.el
+++ b/dash.el
@@ -1959,6 +1959,22 @@ The test for equality is done with `equal',
or with `-compare-fn' if that's non-nil."
(--filter (not (-contains? list2 it)) list))
+(defun -powerset (list)
+ "Return the power set of LIST."
+ (if (null list) '(())
+ (let ((last (-powerset (cdr list))))
+ (append (mapcar (lambda (x) (cons (car list) x)) last)
+ last))))
+
+(defun -permutations (list)
+ "Return the permutations of LIST."
+ (if (null list) '(())
+ (apply #'append
+ (mapcar (lambda (x)
+ (mapcar (lambda (perm) (cons x perm))
+ (-permutations (remove x list))))
+ list))))
+
(defun -contains? (list element)
"Return non-nil if LIST contains ELEMENT.
diff --git a/dev/examples.el b/dev/examples.el
index a35ae33..092e57e 100644
--- a/dev/examples.el
+++ b/dev/examples.el
@@ -565,6 +565,15 @@ new list."
(-intersection '(1 2 3) '(4 5 6)) => '()
(-intersection '(1 2 3 4) '(3 4 5 6)) => '(3 4))
+ (defexamples -powerset
+ (-powerset '()) => '(nil)
+ (-powerset '(x y z)) => '((x y z) (x y) (x z) (x) (y z) (y) (z) nil))
+
+ (defexamples -permutations
+ (-permutations '()) => '(nil)
+ (-permutations '(1 2)) => '((1 2) (2 1))
+ (-permutations '(a b c)) => '((a b c) (a c b) (b a c) (b c a) (c a b) (c b
a)))
+
(defexamples -distinct
(-distinct '()) => '()
(-distinct '(1 2 2 4)) => '(1 2 4)))
