Clojure - Calculate with big numbers

Question

I want to calculate !1000 in clojure, how can I do this without getting a integer-overflow exception?

My factorial code is right now: (reduce * (range 1 1001)).

Answer 1

You could use the *' operator which supports arbitrary precision by automatically promoting the result to BigInt in case it would overflow:

(reduce *' (range 1 1001))

Answer 2

Put N at the end of the number which makes it a bigint,

(reduce * (range 1N 1001N))

Answer 3

Coerce the parameters to clojure.lang.BigInt

(reduce * (range (bigint 1) (bigint 1001)))

I.e. if you are working with an third-party library that doesn't use *'

(defn factorial' [n]
   (factorial (bigint n)))