ikarus/benchmarks/rnrs-benchmarks/ntakl.ss

;;; NTAKL -- The TAKeuchi function using lists as counters,
;;; with an alternative boolean expression.
   
(library (rnrs-benchmarks ntakl)
  (export main)
  (import (rnrs) (rnrs-benchmarks))

  (define (listn n)
    (if (= n 0)
      '()
      (cons n (listn (- n 1)))))
   
  (define l18 (listn 18))
  (define l12 (listn 12))
  (define  l6 (listn 6))
   
  (define (mas x y z)
    (if (not (shorterp y x))
        z
        (mas (mas (cdr x) y z)
             (mas (cdr y) z x)
             (mas (cdr z) x y))))
   
  ; Part of the fun of this benchmark is seeing how well the compiler
  ; can understand this ridiculous code, which dates back to the original
  ; Common Lisp.  So it probably isn't a good idea to improve upon it.
  
  #;
  (define (shorterp x y)
    (and (not (null? y))
         (or (null? x)
             (shorterp (cdr x)
                       (cdr y)))))
   
  ; But SML/NJ runs this benchmark about 15 times as fast when the
  ; code above is rewritten as follows, so I tried it for Scheme also.
  
  (define (shorterp x y)
    (cond ((null? y) #f)
          ((null? x) #t)
          (else
           (shorterp (cdr x) (cdr y)))))
  
  (define (main . args)
    (run-benchmark
      "ntakl"
      takl-iters
      (lambda (result) (equal? result '(7 6 5 4 3 2 1)))
      (lambda () (lambda () (mas l18 l12 l6))))))