Ruby: All letter combinations of length n

letter_combos.rb

LETTERS = (65..90).collect{|char_code| char_code.chr}

def letter_combos length, accum = nil
  return accum if length == 0
  return accum || LETTERS if length == 1
  combos = (accum || LETTERS).product(LETTERS).inject([]) {|combos, product| 
    combos << product.first + product.last}     
  letter_combos(length - 1, combos)
end

#ex:
# letter_combos(2) => ["AA", "AB", "AC", ... "ZZ"]
# letter_combos(3) => ["AAA", "AAB", "AAC", ... "ZZZ"]

Hm gg ruby? Clojure:

(def letters
  (into [] (for [char-code (range 65 91)] (char char-code))))

(defn letter-combos [len]
  (map str/join (apply clojure.math/cartesian-product (repeat len letters))))

Ruby:

def letter_combos(n)
  letters = (combos = *'a'..'z')
  (n-1).times do combos = letters.product(combos).map{|x| x.join} end
  return combos
end

;D

Haskell?

letter_combos :: Int -> [[Char]]
letter_combos n = (iterate combos [[]]) !! n
                  where combos xs = [l:x | l <- ['a'..'z'], x <- xs]