;; *** before: ***
;; a hand-rolled version, or Java interop that only covers
;; longs and doubles and mishandles ratios and bigints
(defn abs-old [x] (if (neg? x) (- x) x))
(abs-old -7)
;=> 7
(abs-old -1/2)
;=> 1/2

;; *** in version 1.11: ***
;; abs works correctly and efficiently for every numeric type
(abs -7)
;=> 7
(abs -1/2)
;=> 1/2
(abs -7.5)
;=> 7.5