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