(続々)Gaucheで「カブらない数字を4桁だすの」をやる*1

http://d.hatena.ne.jp/n9d/20071120/1195568232

で、shiroさんに教えて頂いたのでもう少しやってみる。

gauche.sequenceを使う方法

>> (begin (use srfi-1) (use gauche.sequence) (take (shuffle (iota 10)) 4))
=> (8 9 5 0)

append-mapを使う方法

やばい、今度は引数の勉強しなきゃいけなくなった。

>> (use util.combinations)(use srfi-27)
=> #<undef>

>> => #<undef>

>> (define permutations2 (lambda (x y) (append-map permutations (combinations x y))))
=> permutations2

>> (let ((a (permutations2 (iota 10) 4))) (list-ref a (random-integer (length a))))
=> (6 2 0 5)

可変引数に対応したバージョンのpermutationsをつくる

>> (use util.combinations)
=> #<undef>
>> (define permutations.super permutations)
=> permutations.super
>> (define permutations (lambda (x . y) (if (null? y) (permutations.super x) (append-map permutations.super (combinations x (car y))))))
=> permutations
>> (permutations '(1 2 3))
=> ((1 2 3) (1 3 2) (2 1 3) (2 3 1) (3 1 2) (3 2 1))
>> (permutations '(1 2 3) 2)
=> ((1 2) (2 1) (1 3) (3 1) (2 3) (3 2))