haskell - 为什么 "++"功能比 ":"贵得多？-6ren

haskell - 为什么 "++"功能比 ":"贵得多？

转载作者：行者123 更新时间：2023-12-01 22:05:15

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以下这段话来自Learn You a Haskell for Great Good!

"Watch out when repeatedly using the ++ operator on long strings. When you put together two lists (even if you append a singleton list to a list, for instance: [1,2,3] ++ [4]), internally, Haskell has to walk through the whole list on the left side of ++. That's not a problem when dealing with lists that aren't too big. But putting something at the end of a list that's fifty million entries long is going to take a while. However, putting something at the beginning of a list using the : operator (also called the cons operator) is instantaneous."

我不知道为什么 Haskell 必须遍历++ 左侧的整个列表。