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digego / extempore

A cyber-physical programming environment
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Recursion causes a segfault #309

Closed cianoc closed 6 years ago

cianoc commented 6 years ago 
(bind-func fact
  (lambda (n)
    (let ((p (- n 1)))
      (if (<= n 0) (1)
        (* n (fact p))))))

(bind-func fact3
  (lambda (n)
    (let ((total 1))
      (while (> n 0)
        (set! total (* total n))
        (set! n (- n 1)))
      (println total))))

Running ($ (println (fact 1600000))) results in a segfault. In contrast running: (fact3 1600000) does not.

This would suggest that tail optimization isn't implemented for xtlang.

digego commented 6 years ago

Hey Cian,

;; not tail recursive (bind-func fact1 (lambda (n) (if (<= n 0) 1 (* n (fact1 (- n 1))))))

;; tail recursive (bind-func fact2 (lambda (nn) (let ((f (lambda (n k) (if (<= n 0) k (f (- n 1) (* (i64tod n) k)))))) (f nn 1.0))))

From: cianoc Sent: Tuesday, 2 January 2018 11:54 AM To: digego/extempore Cc: Subscribed Subject: [digego/extempore] Recursion causes a segfault (#309)

(bind-func fact (lambda (n) (let ((p (- n 1))) (if (<= n 0) (1) (* n (fact p)))))) (bind-func fact3 (lambda (n) (let ((total 1)) (while (> n 0) (set! total (* total n)) (set! n (- n 1))) (println total)))) Running($ (println (fact 1600000)))results in a segfault. In contrast running:(fact3 1600000) does not. This would suggest that tail optimization isn't implemented for xtlang. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub, or mute the thread.

cianoc commented 6 years ago

Ah gotcha. I will close this issue once I've got something written about it.

If I had a nickel for every time I'd made that mistake I'd have a lot of nickels by now.