CODEWITHSUNDEEP
clojureschemetail-recursiontail-call-optimization
tkf
tkf

Reputation: 1070

Tail Call Elimination in Clojure?

Can somebody rewrite this (plt) Scheme code into Clojure?

(define (f n)
   (printf "(f ~a)~n" n)
   (g n))

(define (g n)
   (printf "(g ~a)~n" n)
   (h n))

(define (h n)
   (printf "(h ~a)~n" n)
   (f (+ n 1)))

In such a way as to not collapse the procedures f, g, and h together and to allow the code to run indefinitely without crashing?

Upvotes: 17

Views: 688

Answers (1)

Nathan Hughes
Nathan Hughes

Reputation: 96385

Use a trampoline:

(declare f)

(defn h [n]
   (println "(h " n ")")
   #(f (+ n 1)))

(defn g [n]
   (println "(g " n ")")
   #(h n))

(defn f [n]
   (println "(f " n ")")
   #(g n))

Kick it off with:

(trampoline f 0)

I've had this code running on my pc in the background for about 5 hours now and the memory usage is flat.

Upvotes: 30

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