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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: processing a sequence
Date: Fri, 30 Aug 2024 22:10:07 -0000 (UTC)
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joswig@....  wrote:

> > I am trying to process a sequence like:
> >
> > (0 1 2 3 0 1 2 3 0 1 2 3)
> >
> > and produce:
> >
> > ((0 1 2 3)(0 1 2 3)(0 1 2 3))
> >
> > i.e. create sub-sequences beginning whenever the value decreases.
> >

Gauche Scheme

(monotonic-slices '(0 1 2 3 0 1 2 3 0 1 2 3) + >)

  ===>
((0 1 2 3) (0 1 2 3) (0 1 2 3))


Given:

(define (each-mono-slice func LST :optional (KEY-FUNC values) (CMP equal?))
  (let ((RESULT '())  (TMP '())  (OLD-KEY 0)  (NEW-KEY 0))
    (dolist (X LST)
      (set! NEW-KEY (KEY-FUNC X))
      (cond ((null? TMP) (push! TMP X))
            ((CMP NEW-KEY OLD-KEY)
             (push! TMP X))
            (#t (func (reverse TMP)) (set! TMP (list X))))
      (set! OLD-KEY NEW-KEY))
    (unless (null? TMP) (func (reverse TMP)))
    (reverse RESULT)))

(define (monotonic-slices LST :optional (KEY-FUNC values) (CMP equal?))
  (let ((result '()))
    (each-mono-slice (lambda(xs) (push! result xs)) LST KEY-FUNC  CMP)
    (reverse result)))