Sha256: 91abdf98f444360c1669cf2063e1f4f25aaa601ab664957619e3341616b3b681
Contents?: true
Size: 780 Bytes
Versions: 107
Compression:
Stored size: 780 Bytes
Contents
(ns luhn)
(defn to-reversed-digits
"returns a lazy sequence of least to most significant digits of n"
[n]
(->> [n 0]
(iterate (fn [[i _]] [(quot i 10) (mod i 10)]))
(take-while (complement #{[0 0]}))
(map second)
rest))
(defn checksum
"returns the luhn checksum of n, assuming it has a check digit"
[n]
(-> (->> n
to-reversed-digits
(map * (cycle [1 2]))
(map #(if (>= % 10) (- % 9) %))
(apply +))
(mod 10)))
(defn valid?
"whether n has a valid luhn check-digit"
[n]
(zero? (checksum n)))
(defn add-check-digit
"given a number, adds a luhn check digit at the end"
[n]
(let [n-shifted (* 10 n)
check-digit (- 10 (checksum n-shifted))]
(+ n-shifted check-digit)))
Version data entries
107 entries across 107 versions & 1 rubygems