string_calculator.clj

(ns string_calculator
  (:use clojure.contrib.str-utils))

(defn add-numbers [s]
  (reduce + (map #(check-num %)
                 (filter #(not= "" %) (re-split #"," s)))))

(defn check-num [i]
  (let [intr (Integer. i)]
                    (if (> 0 intr)
                      (throw (IllegalArgumentException. "No negative numbers"))
                      intr)))

(defn normalize-newlines [s]
  (.replaceAll (normalize-custom s) "\n" ","))

(defn normalize-custom [s]
  (if (.contains s "//")
    (let [[s delim-spec] (re-matches #"//(.*)\n.*" s)
          delimiter (java.util.regex.Pattern/quote delim-spec)]
      (.replaceAll (nth (re-split #"\n" s) 1)
                   delimiter
                   ","))
    s))

(defn add [s] (if (empty? s)
                0
                (add-numbers (normalize-newlines s))))

string_calculator_test.clj

(ns string-calculator-test
  (:use clojure.test string_calculator))

(deftest returns_0
  (is (= (add "") 0)))

(deftest returns_bare
  (is (= (add "1") 1))
  (is (= (add "2") 2)))

(deftest adds_numbers
  (is (= (add "1,2") 3))
  (is (= (add "1,1") 2)))

(deftest newline_as_delimiter
  (is (= (add "1\n2") 3))
  (is (= (add "1\n1") 2)))

(deftest custom_delimiter
  (is (= (add "//+\n1+2") 3))
  (is (= (add "//;\n1;3") 4))
  (is (= (add "//abc\nabc1abc2") 3))
  (is (= (add "//po\npo1po1") 2)))

(deftest no_negatives
;; This test fails
  (is (thrown? IllegalArgumentException (add "-1"))) ;; This test fails
  (is (= (add "//-\n1-2") 3)))