isAlpha和isLetter有什么区别？

问题描述

在Haskell中，函数 Data.Char.isAlpha 检查字符是否为字母， Data.Char.isLetter 。

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?

推荐答案

查看，它们似乎是等同的。

Looking at the sources they appear to be equivalent.

以下是4.3.1.0中定义的 isLetter 的定义

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

并且 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

具有不同的实现，但是它们具有相同的效果。

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

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