sum-of-even-numbers.scm

#|
Benchmark: ran srfi-42-sum, apply-filter-iota, fold-lseq, recursive-loop, each for 1000 times.
        srfi-42-sum:  3.722 real,  3.720 cpu ( 3.720 user + 0.000 sys)@268.82/s n=1000
  apply-filter-iota: 14.721 real, 23.980 cpu (23.840 user + 0.140 sys)@ 41.70/s n=1000
          fold-lseq: 43.668 real, 50.560 cpu (50.460 user + 0.100 sys)@ 19.78/s n=1000
     recursive-loop:  4.371 real,  4.370 cpu ( 4.370 user + 0.000 sys)@228.83/s n=1000

                     Rate srfi-42-sum apply-filter-iota fold-lseq recursive-loop
        srfi-42-sum 269/s          --             6.446    13.591          1.175
  apply-filter-iota  42/s       0.155                --     2.108          0.182
          fold-lseq  20/s       0.074             0.474        --          0.086
     recursive-loop 229/s       0.851             5.487    11.570             --
|#

(use gauche.time)
(use srfi-42)

(define (srfi-42-sum n)
  (sum-ec (:range i 1 n) (if (even? i)) i))

(define (apply-filter-iota n)
  (apply + (filter even? (iota n 1))))

(define (fold-lseq n)
  (fold + 0 (lfilter even? (liota n 1))))

(define (recursive-loop n)
  (let loop ([i 1] [s 0])
    (if (= i n) s (loop (+ i 1) (if (even? i) (+ s i) s)))))

(define N 100000)

($ time-these/report 1000
   `((srfi-42-sum       . ,(cut srfi-42-sum N))
     (apply-filter-iota . ,(cut apply-filter-iota N))
     (fold-lseq         . ,(cut fold-lseq N))
     (recursive-loop    . ,(cut recursive-loop N))))