isAlpha和isLetter有什么区别？(What is the difference between isAlpha and isLetter?)

在Haskell中，函数Data.Char.isAlpha检查一个字符是否是字母，但Data.Char.isLetter也是如此。这些功能之间有没有真正的区别，还是可以互换？

In Haskell, the function Data.Char.isAlpha checks if a character is a letter, but so does Data.Char.isLetter. Is there any real difference between these functions, or are they interchangeable?

最满意答案

看他们似乎是相同的来源。

这是isLetter中定义的isLetter的定义

-- derived character classifiers -- | Selects alphabetic Unicode characters (lower-case, upper-case and -- title-case letters, plus letters of caseless scripts and modifiers letters). -- This function is equivalent to 'Data.Char.isAlpha'. isLetter :: Char -> Bool isLetter c = case generalCategory c of UppercaseLetter -> True LowercaseLetter -> True TitlecaseLetter -> True ModifierLetter -> True OtherLetter -> True _ -> False

而isAlpha的定义是：

-- | Selects alphabetic Unicode characters (lower-case, upper-case and -- title-case letters, plus letters of caseless scripts and modifiers letters). -- This function is equivalent to 'Data.Char.isLetter'. isAlpha :: Char -> Bool isAlpha c = iswalpha (fromIntegral (ord c)) /= 0

他们似乎有不同的实现，但它们被记录为具有相同的效果。

Looking at the sources they appear to be equivalent.

Here is the definition of isLetter as defined in 4.3.1.0

-- derived character classifiers -- | Selects alphabetic Unicode characters (lower-case, upper-case and -- title-case letters, plus letters of caseless scripts and modifiers letters). -- This function is equivalent to 'Data.Char.isAlpha'. isLetter :: Char -> Bool isLetter c = case generalCategory c of UppercaseLetter -> True LowercaseLetter -> True TitlecaseLetter -> True ModifierLetter -> True OtherLetter -> True _ -> False

And the definition of isAlpha:

-- | Selects alphabetic Unicode characters (lower-case, upper-case and -- title-case letters, plus letters of caseless scripts and modifiers letters). -- This function is equivalent to 'Data.Char.isLetter'. isAlpha :: Char -> Bool isAlpha c = iswalpha (fromIntegral (ord c)) /= 0

They appear to have different implementations, but they are documented to have the same effect.

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