Janken script supporting more than two hands

janken.scm

;;; -*- mode: scheme; coding: utf-8 -*-
(use util.match)
(define (which-win hand-left hand-right)
  (match (list hand-left hand-right)
    [(or ('g 'g) ('p 'p) ('c 'c)) #f]
    [(or ('g 'p) ('p 'c) ('c 'g)) hand-right]
    [(or ('p 'g) ('c 'p) ('g 'c)) hand-left]
    [else (errorf "Unknown hand: left ~a, right ~a" hand-left hand-right)]))
;; gosh> (janken 'g 'p)
;; p
;; gosh> (janken 'g 'p 'g)
;; p
;; gosh> (janken 'g 'p 'g 'c)
;; #f
(define (janken . args)
  (let1 t (make-hash-table 'eq?)
    (for-each (cut hash-table-put! t <> #t) args)
    (let1 hands (hash-table-keys t)
      (if (= 2 (length hands))
          (apply which-win hands)
          #f))))