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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: Confused about Scheme...???
Date: Tue, 6 Aug 2024 15:37:40 -0000 (UTC)
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B. Pym wrote:

> >     In short, 'reduce-list', is take a list of variable length, 'b',
> > below and reduce it if the (caar ls) and (caadr ls) are equal...this
> > is the first atom within the pair of consecutive sublists and if this
> > is true contruct a list,  (list (caar ls) (+ (cadar ls) (cadadr ls)))
> > , and add second atom of the consective pairs.  For example,
> > (reduce-list b) ==> ((4 3) (3 7) (2 1) (1 2) (0 1)).  I can get it to
> > work for the first two terms without using recursion, produces (4 3),
> > but when I implement recursion it barfs.  Could some one tell me what
> > I'm doing wrong because I know that I'm trying to do to much at once?
> > 
> > 
> > -Conrad
> > 
> > 
> > (define (reduce-list ls)
> >     (cond ((null? ls) ls)
> >     (else
> >       (cond ((null? (cadr ls)) ls)
> >       (else
> >         (cond ((eq? (caar ls) (caadr ls))
> >                  (list (caar ls) (+ (cadar ls) (cadadr ls)))
> >                  (reduce-list (cdr ls)))
> >               (else (list (car ls) (reduce-list (cdr ls)))))))))))
> > 
> > 
> > (define b '((4 1) (4 2) (3 3) (3 4) (2 1) (1 2) (0 1)))
> > 
> > (reduce-list b)
> 
> newLISP
> 
> (define b '((4 1) (4 2) (4 80) (3 3) (3 4) (2 6) (9 2) (9 5)))
> 
> (define (meld xs)
>   (local (K A B)
>     (if (null? xs)
>       '()
>       (let (u (unify '((K A) (K B)) (0 2 xs)))
>         (if u
>           (begin (bind u) (meld (cons (list K (+ A B)) (2 xs))))
>           (cons (first xs) (meld (rest xs))))))))
> 
> (meld b)
> 
> ((4 83) (3 7) (2 6) (9 7))

Shorter:

(define (meld xs  , K A B)
  (if (null? xs)
    '()
    (if (unify '((K A) (K B)) (0 2 xs))
      (begin (bind $it) (meld (cons (list K (+ A B)) (2 xs))))
      (cons (first xs) (meld (rest xs))))))