It has been nagging me as to how cond returns a positive value in function, when a negative value is passed to its x parameter. My idea is that two negatives multiplied produce a positive, but this seems quite confusing as there appears to be no multiplication occurring anywhere in the function.
Could someone give me an detailed explanation of why a negative value passed to x returns a positive value?
(def abs
(fn [x]
(cond (> x 0) x
(= x 0) 0
(< x 0) (- x))))
(abs -10) -> 10
The code is a variation of the abs function found in the book SICP, but written in Clojure.
Kind regards
When the number is negative, (< x 0), we negate it, (- x), to get a positive number of the same magnitude. You can think of negation as multiplication by -1 if you like.
(doc -) ------------------------- clojure.core/- ([x] [x y] [x y & more]) If no ys are supplied, returns the negation of x, else ...