(rand) (rand n)
Returns a random floating point number between 0 (inclusive) and n (default 1) (exclusive).
;; Test `rand` never returns `n`:
user=> (some (partial <= 10) (take 100000 (repeatedly (fn [] (int (rand 10))))))
nil
user=> (rand)
0.17469201779243182
user=> (rand 100)
49.542391492950834