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
next prev parent 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
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