String calculator kata in Clojure done early while learning the language.

core.clj

(ns string-calculator.core
  (:require [clojure.string :refer [join]]))

(defn numbers-from-string
  [string]
  (map #(Integer. %) (re-seq #"-?\d+" string)))

(defn add
  [string]
  (if (empty? string) 0
      (let [numbers (numbers-from-string string)
            negatives (filter #(< % 0) numbers)]
        (if (not (empty? negatives))
          (throw (Exception. (str "Negative numbers are not allowed: "
                                  (join ", " negatives))))
          (reduce + (filter #(<= % 1000) numbers))))))

(defn a [s]
  (if (= "" s) 0
      (let [n (map #(Integer. %) (re-seq #"-?\d+" s)) n- (filter #(< % 0) n)]
        (if (< 0 (count n-)) (throw (Exception. (str "Negative numbers are not allowed: " (join ", " n-))))
            (reduce + (filter #(<= % 1000) n))))))

core_test.clj

(ns string-calculator.core-test
  (:require [clojure.test :refer :all]
            [string-calculator.core :refer :all]))

(deftest string-calculator

  (testing "adding an empty string"
    (is (= 0 (add ""))))

  (testing "adding one number"
    (is (= 2 (add "2"))))

  (testing "adding two numbers"
    (is (= 3 (add "1,2"))))

  (testing "adding numbers separated by newline"
    (is (= 6 (add "1\n2,3"))))

  (testing "adding numbers separated by custom delimiter"
    (is (= 3 (add "//[;]\n1;2"))))

  (testing "adding negative numbers throws exception with negatives"
    (is (thrown-with-msg? Exception #"Negative numbers are not allowed: -3, -1"
                          (add "2,-3,2,-1"))))

  (testing "adding numbers separated by multi-character delimiter"
    (is (= 3 (add "//[***]\n1***2"))))

  (testing "numbers larger than 1000 are ignored"
    (is (= 1001 (add "1,1000,1001"))))

  (testing "adding numbers separated by multiple delimiters"
    (is (= 6 (add "//[;;][&/]\n1;;2&/3")))))