I've started reading SICP and I came across the Fermat primality test
implemented an Scheme. I reimplemented it in Clojure and was able to
switch the recursive call in fast-prime to TCO/recur, but I was unable
to do the same for the exp-mod function.
(defn exp-mod [base exp m]
(cond
(zero? exp) 1
(even? exp) (mod (Math/sqrt (exp-mod base (/ exp 2) m)) m)
:else (mod (* base (exp-mod base (inc exp) m)) m)))
(defn fermat-test [n]
(defn try-it [a]
(= (exp-mod a n n) a))
(try-it (inc (rand-int (dec n)))))
(defn fast-prime? [n times]
(cond
(zero? times) true
(fermat-test n) (recur n (dec times))
:else false))
Calling (fast-prime? 5 3) blows the stack. How can I change exp-mod to use TCO?
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