September 2014
Intermediate to advanced
336 pages
7h 53m
Japanese
Content preview from アンダースタンディング コンピュテーション ―単純な機械から不可能なプログラムまで
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278
8
章 不可能なプログラム
opposite.rb < do_the_opposite.rbは永久にループします。すなわち、実際に起こることに対して、
#halts_on_itself?
は間違った答えを返しているということです。これに対して、もし
#halts_
on_itself?
が
false
を返すと、do_the_opposite.rbは即座に停止します。これも
#halts_on_
itself?
による予測と矛盾することになります。
ここで
#halts_on_itself?
を責めるのは間違いです。このメソッドは
#halts?
に委譲して答え
をリレーしているワンライナーにすぎません。ここで実際にわかったことは、
program
と
input
とい
う引数を両方ともdo_the_opposite.rbにして
#halts?
を呼び出したとき、
#halts?
は満足のいく答
えを返せないということです。どれだけがんばっても、得られる結果はおのずと間違ったものになりま
す。つまり、
#halts?
の真の実装には2 つの運命しかないということです。
●
#halts?
は間違った答えを返すことがある。たとえば、do_the_opposite.rbは停止するのに、
永久にループすると予測するなど。
●
#halts?
は永久にループして答えを返さないことがある。たとえば、
#evaluate
がruby
does_it_say_no.rb < does_it_say_no.rbでやったように。
したがって、完全に正しい
#halts ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.