Sujet : Re: Another code review perhaps?
De : 643-408-1753 (at) *nospam* kylheku.com (Kaz Kylheku)
Groupes : comp.lang.lisp comp.lang.schemeDate : 12. Sep 2024, 14:22:24
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <20240912051355.168@kylheku.com>
References : 1
User-Agent : slrn/pre1.0.4-9 (Linux)
On 2024-09-12, B. Pym <
Nobody447095@here-nor-there.org> wrote:
Arthur Lemmens wrote:
>
Define iterative and recursive versions of a function that takes an
object x and a vector v, and returns a list of all the objects that
immediately precede x in v.
Graham doesn't like LOOP, but I do. So here's a LOOP-version:
(defun precedes (object vector)
(loop for x across vector
and i from 0
when (and (equal x object) (> i 0))
collect (elt vector (1-i))))
>
>
Look at that:
>
(1-i)
>
Don't you think that that should be:
>
(1- i)
>
or
>
(- i 1)
>
?
>
It's shorter when you use a Lispy language instead of CL.
>
Gauche Scheme
>
(use srfi-42) ; list-ec
>
(define (precedes obj vec)
(list-ec (: x (index i) vec)
(if (and (> i 0) (equal? x obj)))
(ref vec (- i 1))))
>
(precedes 5 #(5 0 4 5 8 9 5))
===>
(4 9)
>
Another way:
>
(define (precedes o v)
(let ((l (vector->list vec)))
(filter-map
(^(a b) (and (equal? o a) b))
(cdr l)
l)))
1> (match @(scan-all (@x 5 . @nil)) '(5 0 4 5 8 9 5) x)
(4 9)
2> (window-mappend 1 nil (do if (and @1 (= @2 5)) (list @1)) #(5 0 4 5 8 9 5))
#(4 9)
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