unofficial mirror of guile-user@gnu.org 
 help / color / mirror / Atom feed
From: Tim Van den Langenbergh <tmt_vdl@gmx.com>
To: guile-user@gnu.org
Subject: Re: guile style
Date: Sat, 19 Jun 2021 12:25:13 +0200	[thread overview]
Message-ID: <1707718.159HRY3vo4@terra> (raw)
In-Reply-To: <7aeef132-6bd7-c178-5786-c0a3d6b3edc8@nycap.rr.com>

On Saturday, 19 June 2021 02:55:34 CEST jerry wrote:
> I am fairly new to guile and scheme. People tell me that I should use a
> functional style.
>
> I have 3 solutions for project euler problem #1. The first is
> functional, the second is imperative and the third is written in "Little
> Schemer" style.
>
> I was hoping other guile users would comment on preferences or the
> "correct way". Sorry in advance for any wrapping problems that may occur.
>
> #!/usr/local/bin/guile  -s
> !#
> (use-modules (srfi srfi-1) (jpd stdio)) ;; for folds
> (define N 1000)
>
> (define ans
>    (fold + 0
>      (filter
>        (lambda (x) (or (= 0 (modulo x 3)) (= 0 (modulo x 5))))
>        (iota N))))
> (print ans)
>
> (define ans 0)
> (for i N
>    (if (or (= 0 (modulo i 3)) (= 0 (modulo i 5))) (set! ans (+ ans i))))
> (print ans)
>
> (define ans
>    (let loop ((i 1) (ans 0))
>      (cond
>        ((>= i N) ans)
>        ((or (= 0 (modulo i 3)) (= 0 (modulo i 5))) (loop (1+ i) (+ ans i)))
>        (else (loop (1+ i) ans)) )))

I'm not 100% sure about how Guile does it, but I know that some Scheme
implementations do some boxing for set! operations, which will make the second
variation poorly optimised. Personally I would use combine the first and third
answers by doing the divisible-by check during the fold, like this:

(use-modules (srfi srfi-1))

(define (divisible-by? divident divisor)
~~(zero? (modulo divident divisor)))

(define N 1000)

(define ans
~~(fold (lambda (i res)
~~~~~~~~~~(if (or (divisible-by? i 3)
~~~~~~~~~~~~~~~~~~(divisible-by? i 5))
~~~~~~~~~~~~(+ i res)
~~~~~~~~~~~~res))
~~~~~~~~0
~~~~~~~~(iota N)))

Vale,

-Tim





  reply	other threads:[~2021-06-19 10:25 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-19  0:55 guile style jerry
2021-06-19 10:25 ` Tim Van den Langenbergh [this message]
     [not found]   ` <CAGua6m1HSYGP6i60Qyj=sVAgeriOzZmb1abCtoxnTQQiOgyY-Q@mail.gmail.com>
2021-06-19 11:24     ` Fwd: " Stefan Israelsson Tampe
2021-06-19 11:31   ` jerry
2021-06-19 11:17 ` Ricardo Wurmus
2021-06-19 11:20 ` Christopher Lam
2021-06-19 12:16   ` jerry
2021-06-19 17:02     ` Zelphir Kaltstahl
2021-06-19 17:59     ` Linus Björnstam
2021-06-20  2:21       ` jerry

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: https://www.gnu.org/software/guile/

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1707718.159HRY3vo4@terra \
    --to=tmt_vdl@gmx.com \
    --cc=guile-user@gnu.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).