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 6 章
雖然這對 FizzBuzz 問題依然是有意義的解決方案，但現在這是我們只使用 proc 來實作
的機會。
儘管它很簡單，但如果我們沒有程式語言的任何功能，這會是非常具有野心、抱負
的程式：它建立範圍、映射到它、估算大條件、以模數運算子完成算術運算、使用
Fixnum#zero?
述語、使用一些字串常值，而且會以
Fixnum#to_s
將數值轉換成字串。
這是相當大量的 Ruby 內建功能，我們不得不全數刪除，並且重新以 proc 實作。
數值
我們首先將焦點放在出現在 FizzBuzz 的數值。怎麼做可以不使用 Fixnums 或 Ruby 提
供的任何其他資料型別而能表示數值？
如果想要試著從頭開始實作數值
3
， 最好對自己正在實作的內容能有充分的瞭解。不管
如何，究竟何謂
數值
？這實在很難從我們剛好正在定義的某些假設觀點給個具體的解
釋；例如，『告訴我們有多少…』就不是很實用，因為『多少』真的只是另一種『數值』
說法。
這裡有一種描述數值特徵的方式：想像我們有一袋蘋果和一袋橘子。我們從某個袋子裡
拿出一個蘋果，也從另一個袋子裡拿出一個橘子，並且將它們放在一邊，然後我們持續
拿出蘋果和橘子，一直到至少其中某個袋子是空的。
如果兩個袋子同時變空，我們就能學到一些有趣的東西：儘管包含的東西不同，但這些
袋子具有一些意謂著它們同時變空的共用特性；每次在反覆從每個袋子移出物品的過
程，兩個袋子都不是空的，或者兩個袋子都是空的。我們可以將這些袋子共用的抽象特
性稱為數值（雖然我們不知道
哪個
號碼！），而且我們可以將這些袋子與世界上其他任 ...
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