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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: macros vs HOFs (was: O'Caml)
Date: Sun, 15 Sep 2024 11:52:03 -0000 (UTC)
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Matthew Danish wrote:

> If you want to have some fun, why not write a nice higher-order function
> to do:
> 
> (defun silly-loop (string &optional (increment 1) (final-char nil))
>   (loop for n from 0 by increment
>         for char across string
>         until (eql char final-char)
>         collect char into char-bag
>         sum n into sum
>         finally (return (values char-bag sum n))))
> 
> Try to make it half as readable.  And as efficient.

Gauche Scheme

(use gauche.sequence) ;; map [generic]

(define (silly str :optional (incr 1) (ender #f))
  (let@ (0 n sum)
    (values
      (map (^(char) (inc! sum n) (inc! n incr) char)
           (if ender
             (car (string-split str ender))
             str))
      sum n)))

(silly "catch" 37 #\h)
  ===>
(#\c #\a #\t #\c)
222
148

(silly "catch")
  ===>
(#\c #\a #\t #\c #\h)
10
5

Given:

(define-syntax let@-aux
  (syntax-rules ()
    [(let@-aux (0 var ...) (pairs ...) stuff)
     (let@-aux () (pairs ... (var 0) ...) stuff)]
    [(let@-aux ('() var ...) (pairs ...) stuff)
     (let@-aux () (pairs ... (var '()) ...) stuff)]
    [(let@-aux (var val more ...) (pairs ...) stuff)
     (let@-aux (more ...) (pairs ... (var val)) stuff)]
    [(let@-aux (var) pairs stuff)
     (let@-aux (var '()) pairs stuff)]
    [(let@-aux () ((var val) ...) (stuff ...))
     (let* ((var val) ...) stuff ...)]))
(define-syntax let@
  (syntax-rules ()
    [(let@ things stuff ...)
     (let@-aux things () (stuff ...))]))