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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: Debugger features
Date: Tue, 1 Jul 2025 04:51:59 -0000 (UTC)
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Alan Crowe wrote:

> Macros let you abstract control structures. For example,
> with a list (a b c d) you might want to compute
> (f a b),(f b c),(f c d)
> Another popular pattern is
> (f a b),(f b c),(f c d)(f d a)
> It is natural to define macros
> 
> * (dolinks (x y '(a b c d ) 'done)(print (cons x y)))
> (A . B)
> (B . C)
> (C . D)
> DONE
> 
> * (docycle (x y '(a b c d ) 'done)(print (cons x y)))
> (A . B)
> (B . C)
> (C . D)
> (D . A)
> DONE
> 
> The alternative is to come up with cliches and use them
> repeatedly in ones code. I've not done too well at coming up
> with cliches taught enough to bear repeated typing; best so
> far:
> 
> * (loop with list = '(a b c d)
>         for x = (car list) then y
>         and y in (cdr list)
>         do (print (cons x y)))
> (A . B)
> (B . C)
> (C . D)
> NIL

Gauche Scheme

(let1 List '(a b c d)
  (for-each
    (lambda(x y) (print (cons x y)))
    List
    (cdr List)))

(a . b)
(b . c)
(c . d)

> 
> * (loop for (x . rest) on '(a b c d)
>         for y = (car rest)
>         when (null rest) do (setf y 'a)
>         do (print (cons x y)))
> (A . B)
> (B . C)
> (C . D)
> (D . A)
> NIL


(use srfi-1)  ;; circular-list

(let1 List '(a b c d)
  (for-each
    (lambda(x y) (print (cons x y)))
    List
    (cdr (apply circular-list List))))

(a . b)
(b . c)
(c . d)
(d . a)