if-not-empty-let

if-not-empty-let.clj

(ns if-not-empty-let.core
  (:require [clojure.test :refer [deftest is run-tests]]))

(defmacro if-not-empty-let
  ([binding then] `(if-not-empty-let ~binding ~then nil))
  ([binding then else]
    (let [form (first binding)
          sequence (binding 1)]
      `(let [temp# ~sequence]
         (if (not (empty? temp#))
            (let [~form temp#]
              ~then)
           ~else)))))

(defn check-rest [x]
  (if-not-empty-let [the-rest (rest x)]
    (str the-rest " is not empty")
    "empty"))

(defn check-even [x]
  (if-not-empty-let [evens (filter even? x)]
    (str "These are even " (vec evens))))

(deftest if-not-empty-let

  (is (= "(2 3) is not empty" (check-rest [1 2 3])))

  (is (= "empty" (check-rest [1])))

  (is (= "These are even [2 4]" (check-even [2 3 4])))

  (is (= nil (check-even [1 3 5])))
)

(run-tests)