Egisonでソウルナンバー (https://twitter.com/twi_carnival/status/732782289604612096) を計算する

soul-number.egi

; num-to-digits from egison-libs https://github.com/egison-libs/project-euler
(define $num-to-digits
  (lambda [$n]
    (map 1#(read (pack {%1})) (unpack (show n)))))

(define $soul-sum
  1#(match (num-to-digits %1) (list integer)
      {[<cons $s ,{}> s]
       [<cons $a $b> (soul-sum (foldl + a b))]}))

(define $main
  (lambda [$args]
    (display
      (soul-sum (read (car args))))))
      
; 実行例
; $ egison soul-number.egi 20111201
; > 8