September 29, 2018
Just Juxt #46: Comparisons (4clojure #166)
For any orderable data type it's possible to derive all of the basic comparison operations (<_ _="_" and="and">) from a single operation (any operator but = or ≠ will work). Write a function that takes three arguments, a less than operator for the data and two items to compare. The function should return a keyword describing the relationship between the two items. The keywords for the relationship between x and y are as follows:
- x = y → :eq
- x > y → :gt
- x < y → :lt
(ns live.test
(:require [cljs.test :refer-macros [deftest is run-tests]]))
(defn comparisons [a b c]
(case (map (juxt a (complement a)) [b c] [c b])
[[true false] [false true]] :lt
[[false true] [false true]] :eq
[[false true] [true false]] :gt))
(deftest comparisons-test
(is (= :gt (comparisons < 5 1)))
(is (= :eq (comparisons (fn [x y] (< (count x) (count y))) "pear" "plum")))
(is (= :lt (comparisons (fn [x y] (< (mod x 5) (mod y 5))) 21 3)))
(is (= :gt (comparisons > 0 2))))
(run-tests)