XPost: comp.lang.scheme

Eric Smith wrote:

; (rm1 "abc" 0) ==> "bc" (rm1 "tea" 1) ==> "ta"
(defun rm1 (seq which)
(remove-if #'true seq :start which :end (1+ which)))

; (consword #\a "bc") ==> "abc"
(defun consword (char word)
(concatenate 'string (string char) word))

; (anagrams "ah") ==> ("ah" "ha")
(defun anagrams (word)
(if (= (length word) 1) (list word)
(loop as x across word
as i upfrom 0
as subword = (rm1 word i)
nconc (loop as y in (anagrams subword)
collect (consword x y)))))

Gauche Scheme

(use util.combinations) ;; permutations

(define (anagrams word)
;; Clojure-style threading or pipelining.
(->> word string->list permutations (map list->string)))

(anagrams "try")
===>
("try" "tyr" "rty" "ryt" "ytr" "yrt")

Given:

(define-syntax ->>
(syntax-rules ()
[(_ x) x]
[(_ x (y ...) z ...)
(->> (y ... x) z ...)]
[(_ x y z ...)
(->> (y x) z ...)]))

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