November 2017
Beginner to intermediate
344 pages
7h 2m
Chinese
Content preview from 深入理解運算原理｜從簡單的機器到無所不能的程式
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第 2 章
意義的『意義』
語言學裡的
語意學
（
semantic
）專門在研究字詞及其意義之間的關聯，例如：『狗』這
個字是頁面上外形的約定，或者是某人聲帶造成的一組空氣震動；這些與實際的狗或一
般對狗的想法截然不同。語意關注的是這些具體的意符如何關聯到它們的抽象意義及抽
象意義本身的基本性質。
在電腦科學的領域，
形式語意
（
formal semantic
）涉及的是程式難以捉摸之意的尋求之
道，以及利用它們發現或證明程式語言的趣事。形式語意的用途廣泛，從像是指定新語
言和設計編譯器最佳化的具體應用，一直到諸如建構程式正確性的數學證明的抽象概
念。
要完全具體詳述某種程式語言，我們需要提供兩件事：一是描述程式外觀的
語法
（
syntax
），再者是描述程式意義的語意
1
。
許多語言並沒有官方的書面規格，只有能運作的直譯器或編譯器。Ruby 本身就屬於這
種『源自實作物的規格』（specification by implementation）的類型：雖然有很多 Ruby
應該如何運作的書籍和教程，但這些資訊的最終來源都是 Matz 的 Ruby Interpreter
（MRI，譯註：Matz 是 Ruby 的原始創造者），這是 Ruby 的參考實作物。如果有任
何 Ruby 文件的隻字片語不同意 MRI 實際的行為，這份就是錯的文件。諸如 JRuby、
Rubinius、MacRuby 之類的第三方 Ruby 實作物都必須竭力且完全模仿 MRI 的行為，
這樣它們才敢聲稱與 Ruby 語言相容。其他像是 PHP
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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.