Problem Statement

An International Securities Identification Number (ISIN) is a unique international identifier for a financial security such as a stock or bond.

Write a function or program that takes a string as input, and checks whether it is a valid ISIN. It is only valid if it has the correct format,   and   the embedded checksum is correct. Demonstrate that your code passes the test-cases listed below.

The format of an ISIN is as follows:

For this task, you may assume that any 2-character alphabetic sequence is a valid country code. The checksum can be validated as follows:

(The comments are just informational.   Your function should simply return a Boolean result.   See #Raku for a reference solution.)

Related task:

Let's start with the solution:

(defn luhn? [cc]
  (let [sum (->> cc
                 (map #(Character/digit ^char % 10))
                 reverse
                 (map * (cycle [1 2]))
                 (map #(+ (quot % 10) (mod % 10)))
                 (reduce +))]
    (zero? (mod sum 10))))

(defn is-valid-isin? [isin]
  (and (re-matches #"^[A-Z]{2}[A-Z0-9]{9}[0-9]$" isin)
       (->> isin
            (map #(Character/digit ^char % 36))
            (apply str)
            luhn?)))

(use 'clojure.pprint)
(doseq [isin ["US0378331005" "US0373831005" "U50378331005" "US03378331005"
              "AU0000XVGZA3" "AU0000VXGZA3" "FR0000988040"]]
  (cl-format *out* "~A: ~:[invalid~;valid~]~%" isin (is-valid-isin? isin)))