learning-sicp

My embarrassing half assed SICP run.
git clone https://kaka.farm/~git/learning-sicp
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exercise-19.scm (451B)

      1 (define-library (sicp solutions chapter-3 exercise-19)
      2   (import (scheme base))
      3   (export cyclic?)
      4 
      5   (begin
      6     (define (cyclic? l)
      7 
      8       (define (cyclic?' tortoise hare)
      9         (cond
     10          ((or (null? hare)
     11               (null? (cdr hare)))
     12           #f)
     13          ((eq? tortoise hare) #t)
     14          (else
     15           (cyclic?' (cdr tortoise)
     16                     (cddr hare)))))
     17 
     18       (if (null? l)
     19           #f
     20           (cyclic?' l (cdr l))))))