> Greetings, Clojure community. I've been playing around with
> clojure,
> and just downloaded 1.3.0. Here's a REPL session, wherein I define
> a power-of-two function, and apply it a couple of times.
>
> lecturer-01:clojure-1.3.0 kangas$ java -cp clojure-1.3.0.jar
> clojure.main
> Clojure 1.3.0
> user=> (defn pow2 [n]
> (loop [n n, p 1]
> (if (zero? n)
> p
> (recur (dec n) (+ p p)) )))
> #'user/pow2
> user=> (pow2 62)
> 4611686018427387904
> user=> (pow2 63)
> ArithmeticException integer overflow
> clojure.lang.Numbers.throwIntOverflow (Numbers.java:1374)
> user=>
>
> Previous versions would silently, automagically convert to bignums
> and
> give me the answer I wanted. Is clojure-1.3.0 too serious,
> enterprisy, and
> Java-like for this sort of thing? I found no clue in the list of
> changes.
This has to do with the primitive math support in Clojure 1.3. Every
number is now a primitive unless otherwise mentioned. `(pow2 63)` is
throwing an exception now because 63 is a primitive int. If you want
`pow2` to work well on large numbers you will have to use the
arbitrary precision math functions like +', -', *', /', etc.
You can also take advantage of BigInteger contagion by switching the
initial value of p to 1N instead of 1.
Thus you can write your function in two ways -
;;; Use arbitrary precision add function. Will return BigInteger when needed.
(defn pow2 [n]
(loop [n n, p 1]
(if (zero? n)
p
(recur (dec n) (+' p p))))) ; +' instead of +
;;; Utilize BigInteger contagion. Will always return BigInteger.
(defn pow2 [n]
(loop [n n, p 1N] ; this is different
(if (zero? n)
p
(recur (dec n) (+ p p)))))
I hope that helps.
Regards,
BG
--
Baishampayan Ghose
b.ghose at gmail.com
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