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Merge pull request #946 from ekaitz-zarraga/faster-concatenate!

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Reduce iterations in concatenate!
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Alex Shinn 2024-01-10 23:45:28 +09:00 • committed by GitHub
commit 97a04bd2fc
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1 changed files with 10 additions and 7 deletions
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17
lib/srfi/1/misc.scm
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@ -15,13 +15,16 @@
(define (concatenate! lists)
(if (null? lists)
'()
(fold (lambda (el acc)
(cond
((null? acc) el)
((null? el) acc)
(else (begin (set-cdr! (last-pair acc) el) acc))))
(car lists)
(cdr lists))))
(let loop ((acc '())
(prev '())
(rem lists))
(cond
((null? rem) acc)
((null? acc) (let ((cur (car rem))) (loop cur cur (cdr rem))))
((null? (car rem)) (loop acc prev (cdr rem)))
(else (let ((cur (car rem)))
(set-cdr! (last-pair prev) cur)
(loop acc cur (cdr rem))))))))
(define (append-reverse rev tail)
(if (null? rev) tail (append-reverse (cdr rev) (cons (car rev) tail))))