On 2015-09-23 09:46AM, Erich Rast wrote:
>Someone on stackoverflow gave me a working implementation in Python 3
>
>https://stackoverflow.com/questions/32694444/
>
>but it uses advanced features and I have no clue how to translate this
>to Racket.
Like this?
#lang racket
(define combinations ; from Rosetta code
(match-lambda**
[(_ 0) '(())]
[('() _) '()]
[((cons x xs) m) (append
(map (curry cons x) (combinations xs (- m 1)))
(combinations xs m))]))
(define (preorders A)
(if (null? A) '(())
(for*/fold ([result '()])
([k (range 1 (+ 1 (length A)))]
[B (combinations A k)]
[order (preorders (set-subtract A B))])
(cons (cons B order) result))))
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