;;;
;;; Travelling Salesman Problem
;;;

(define $station string)  ; 駅は文字列として表現
(define $price   integer) ; 運賃は整数値として表現
(define $graph   (multiset [station (multiset [station price])])) ; 運賃グラフのマッチャー

(define $graph-data ; 運賃データ
  {
   ["東京"   {             ["新宿" 200] ["渋谷" 200] ["三鷹" 390] ["錦糸町" 160] ["北千住" 220]}]
   ["新宿"   {["東京" 200]              ["渋谷" 160] ["三鷹" 220] ["錦糸町" 220] ["北千住" 310]}]
   ["渋谷"   {["東京" 200] ["新宿" 160]              ["三鷹" 310] ["錦糸町" 220] ["北千住" 310]}]
   ["三鷹"   {["東京" 390] ["新宿" 220] ["渋谷" 310]              ["錦糸町" 470] ["北千住" 550]}]
   ["錦糸町" {["東京" 160] ["新宿" 220] ["渋谷" 220] ["三鷹" 470]                ["北千住" 220]}]
   ["北千住" {["東京" 220] ["新宿" 310] ["渋谷" 310] ["三鷹" 550] ["錦糸町" 220]               }]
   })

(define $trips ; 全ての経路をパターンマッチを用いて列挙
  (match-all graph-data graph
    [<cons [,"東京" <cons [$s_1 $p_1] _>]
           (loop $i [2 5]
             <cons [,s_(- i 1) <cons [$s_i $p_i] _>]
                   ...>
             <cons [(& ,"錦糸町" ,s_5) _]
                   _>)>
     [(sum (map (lambda [$i] p_i) (between 1 5)))
      s]]))

(define $main
  (lambda [$args]
    (do {[(print "経路一覧:")]
         [(each (compose show print) trips)]                       ; 全ての経路を出力
         [(write "最安値:")]
         [(print (show (min (map (lambda [$x $y] x) trips))))]}))) ; 最安値を出力