Daily Programmer #399

(ns dp399)

(defn letter?
  [c]
  (or (<= (int \a) (int c) (int \z))
      (<= (int \A) (int c) (int \Z))))

(defn uppercase?
  [c]
  (<= (int \A) (int c) (int \Z)))

(defn char-to-lowercase
  "returns nil if `c` isn't a letter"
  [c]
  (if (not (letter? c))
    nil
    (if (not (uppercase? c))
      c
      (as-> c $
        (int $)
        (- $ (int \A))
        (+ $ (int \a))))))

(defn char-to-num
  "convert a character to a number, where `\\a` is 1 and `\\z` is 26. if given a
  non-alphabetical character, returns nil"
  [c]
  (if (not (letter? c))
    nil
    (as-> c $
      (char-to-lowercase $)
      (int $)
      (- $ (int \a))
      (inc $))))

(defn sum-string-chars
  "get the sum of the string's characters (as converted with `char-to-num`)"
  [s]
  (reduce +
    (as-> s $
      (for [c s :when (letter? c)]
        (char-to-num c)))))