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From: "B. Pym" <Nobody447095@here-nor-there.org>
Newsgroups: comp.lang.lisp,comp.lang.scheme
Subject: Re: Lisp newbie needs help
Date: Fri, 30 Aug 2024 01:15:59 -0000 (UTC)
Organization: A noiseless patient Spider
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B. Pym wrote:

> B. Pym wrote:
> 
> > B. Pym wrote:
> > 
> > > > (defun my-test ()
> > > >    (loop for number = (1+ (random 6))
> > > >          as sum = number then (+ sum number)
> > > >          until (= number 1)
> > > >          do (format t "~&~D thrown. Sum: ~D" number sum)
> > > >          finally (format t "~&One thrown.")))
> > > 
> > > Gauche Scheme
> > > 
> > > (use srfi-1)  ;; unfold
> > > (use srfi-27) ;; random-integer
> > > 
> > > (define (my-test)
> > >   (fold
> > >     (^(n sum) (print n " thrown.  Sum: " (inc! sum n)) sum)
> > >     0
> > >     (cdr (unfold zero? ($ + 1 $) (^_ (random-integer 6)) -1)))
> > >   (print "One thrown."))
> > > 
> > > 
> > > gosh> (my-test)
> > > 2 thrown.  Sum: 2
> > > 2 thrown.  Sum: 4
> > > 6 thrown.  Sum: 10
> > > One thrown.
> > > 
> > > gosh> (my-test)
> > > One thrown.
> > > 
> > > 
> > > Explanation of "unfold":
> > > 
> > > Function: unfold end-test key gen-next-seed seed :optional tail-gen
> > > 
> > > (unfold zero? (lambda(n) (+ 800 n)) (lambda(n) (- n 1)) 7)
> > >   ===>
> > > (807 806 805 804 803 802 801)
> > > 
> > > (unfold zero? (lambda(n) (+ 800 n)) (lambda(n) (- n 1)) 7
> > >   (lambda(n) (list "The number" n "ended the unfolding.")))
> > >   ===>
> > > (807 806 805 804 803 802 801 "The number" 0 "ended the unfolding.")
> > 
> > Using "do" is a bit tricky, but the result is shorter.
> > 
> > (define (my-test)
> >   (do ((n #f (+ 1 (random-integer 6)))
> >        (sum 0))
> >     ((eqv? 1 n) (print "One thrown."))
> >     (if n (print n " thrown.  Sum: " (inc! sum n)))))
> 
> It seems to me that "do*" is more appropriate for this,
> but this version is 2 characters longer!
> 
> (define (my-test)
>   (do* ((n #f (+ 1 (random-integer 6)))
>         (sum 0 (+ n sum)))
>     ((eqv? 1 n) (print "One thrown."))
>     (if n (print n " thrown.  Sum: " sum))))
> 
> I don't know why Common Lisp has "do*", but Gauche, Racket,
> and Chicken Scheme don't.
> 
> Here's a version that I cobbled together.  (A macro guru
> may give us a better one.)  "do" is to "do*" as "let" is
> to "let*".
> 
> (define-syntax do*-aux
>   (syntax-rules ()
>     [(do* (inits ...) ((var update) ...) (test expr ...) stuff ...)
>      (let* (inits ...)
>        (if test
>          (begin expr ...)
>          (begin
>            (begin stuff ...)
>            (let loop ()
>              (begin (set! var update) ...)
>              (if test
>                (begin expr ...)
>                (begin  stuff ...
>                  (loop)))))))]))
> 
> (define-syntax do*
>   (syntax-rules (!!!)
>     [(do* !!! (inits ...) (updates ...)
>        ((var init update) more ...) until body ...)
>      (do* !!! (inits ... (var init)) (updates ... (var update))
>        (more ...) until body ...)]
>     [(do* !!! (inits ...) (updates ...)
>        ((var init) more ...) until body ...)
>      (do* !!! (inits ... (var init)) (updates ... )
>        (more ...) until body ...)]
>     [(do* !!! inits updates () until body ...)
>      (do*-aux inits updates until body ...)]
>     [(do* inits-updates until stuff ...)
>      (do* !!! () () inits-updates until stuff ...)]))
> 
> (do* ((x 0 (+ 1 x))
>       (y 922))
>   ((= 9 x) (print 'ok))
>   (print x " " y))
> 
> 0 922
> 1 922
> 2 922
> 3 922
> 4 922
> 5 922
> 6 922
> 7 922
> 8 922
> ok
>  

Another way:

(define (my-test)
  (let1 r (cut  + 1 (random-integer 6))
    (do* ((n (r) (r))
          (sum n (+ n sum)))
      ((eqv? 1 n) (print "One thrown."))
      (print n " thrown.  Sum: " sum))))