2015年6月24日水曜日

開発環境

Land of Lisp (M.D. Conrad Barski (著)、川合 史朗 (翻訳)、オライリージャパン)の5章(テキストゲームのエンジンを作る)、5.3(特定の場所にあるオブジェクトを描写する)を Scheme で取り組んでみる。

5.3(特定の場所にあるオブジェクトを描写する)

コード(Emacs)

(begin 
  (define print (lambda (x) (display x) (newline)))
  (newline)

  (define map
    (lambda (proc items)
      (if (null? items)
          (quote ())
          (cons (proc (car items))
                (map proc (cdr items))))))
  (define filter
    (lambda (pred items)
      (cond ((null? items) (quote ()))
            ((pred (car items))
             (cons (car items)
                   (filter pred (cdr items))))
            (else (filter pred (cdr items))))))
  
  (define assoc
    (lambda (obj alist)
      (if (null? alist)
          #f
          (let ((item (car alist)))
            (if (equal? obj (car item))
                item
                (assoc obj (cdr alist)))))))

  ;; ここから
  (define *objects* (quote (whiskey bucket frog chain)))
  (define *object-locations* (quote ((whiskey living-room)
                                     (bucket living-room)
                                     (chain garden)
                                     (frog garden))))
  
  (define objects-at
    (lambda (loc objs obj-locs)
      (define at-loc?
        (lambda (obj)
          (let ((item (assoc obj obj-locs)))
            (and item
                 (eq? (cadr item) loc)))))
      ;; Common List の remove-if-not 関数の代わりに、filter 手続きを使用
      (filter at-loc? objs)))
  
  (print (objects-at (quote living-room) *objects* *object-locations*))

  (define describe-objects
    (lambda (loc objs obj-loc)
      (define describe-obj
        (lambda (obj)
          (quasiquote (You see a (unquote obj) on the floor.))))
      (apply append
             (map describe-obj (objects-at loc objs obj-loc)))))

  (print (describe-objects (quote living-room) *objects* *object-locations*))
  
  (quote done))

入出力結果(Terminal(kscheme), REPL(Read, Eval, Print, Loop))

$ kscheme < sample3.scm 
kscm> 
(whiskey bucket)
(You see a whiskey on the floor. You see a bucket on the floor.)
done
kscm> $

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