From: Kazuhiro NISHIYAMA <zn@...>
Date: 2000-11-19T12:35:40+09:00
Subject: [ruby-dev:11601] Re: accumulator, Enumerable#{foldr,foldl}

On Sun, 19 Nov 2000 11:27:39 +0900
Takaaki Tateishi <ttate@jaist.ac.jp> wrote:
>   def foldr(initval)
>     a = initval
>     reverse.each{|x| a = yield(x,a)}  # reverseが定義されないとダメ．
>     a
>   end

reverseの前にreverse_eachがあれば使った方がよさそう。

   def foldr(initval)
     a = initval
     if respond_to? :reverse_each
       reverse_each{|x| a = yield(x,a)}
     elsif respond_to? :reverse
       reverse.each{|x| a = yield(x,a)}
     else
       raise 'reverse_eachかreverseが必要です'
     end
     a
   end


--- 
ZnZ(ゼット エヌ ゼット)
西山和広(Kazuhiro NISHIYAMA)
mailto:zn@mbf.nifty.com