Haskell unicode（UTF-8）字符上的Parsec输出

只需要理解一些与Parsec相关的东西

parseTest (many1 alphaNum) "re2re1Δ"
"re2re1\916"
:t parseTest (many1 alphaNum) 
parseTest (many1 alphaNum) :: Text.Parsec.Prim.Stream s Data.Functor.Identity.Identity Char =>
 s -> IO ()

所以，Unicode的输出应该是UTF-8，因为我在OSX上，十六进制代码应该是希腊的delta字符。 现在，putChar在同一ghci会话和同一终端内不进行相同的转换

Text.Parsec.Char> putChar 'Δ'
Δ

---

为什么？它们都应该只是“Char”类型…？

这里的原因与show和putChar的实现方式有关

λ> show "re2re1Δ"
"\"re2re1\\916\""
λ> mapM_ putChar "re2re1Δ"
re2re1Δ

从源代码中，您可以看到Char的Show实例定义如下：

instance  Show Char  where
    showsPrec _ '\'' = showString "'\\''"
    showsPrec _ c    = showChar '\'' . showLitChar c . showChar '\''

    showList cs = showChar '"' . showl cs
                 where showl ""       s = showChar '"' s
                       showl ('"':xs) s = showString "\\\"" (showl xs s)
                       showl (x:xs)   s = showLitChar x (showl xs s)

putChar         :: Char -> IO ()
putChar c       =  hPutChar stdout c

putChar的实现方式如下：

instance  Show Char  where
    showsPrec _ '\'' = showString "'\\''"
    showsPrec _ c    = showChar '\'' . showLitChar c . showChar '\''

    showList cs = showChar '"' . showl cs
                 where showl ""       s = showChar '"' s
                       showl ('"':xs) s = showString "\\\"" (showl xs s)
                       showl (x:xs)   s = showLitChar x (showl xs s)

putChar         :: Char -> IO ()
putChar c       =  hPutChar stdout c

---

parseTest函数在内部使用print函数，print函数本身在内部使用show，这就是为什么要获取delta的Unicode代码点值。

这里的原因与show和putChar的实现方式有关

λ> show "re2re1Δ"
"\"re2re1\\916\""
λ> mapM_ putChar "re2re1Δ"
re2re1Δ

从源代码中，您可以看到Char的Show实例定义如下：

instance  Show Char  where
    showsPrec _ '\'' = showString "'\\''"
    showsPrec _ c    = showChar '\'' . showLitChar c . showChar '\''

    showList cs = showChar '"' . showl cs
                 where showl ""       s = showChar '"' s
                       showl ('"':xs) s = showString "\\\"" (showl xs s)
                       showl (x:xs)   s = showLitChar x (showl xs s)

putChar         :: Char -> IO ()
putChar c       =  hPutChar stdout c

putChar的实现方式如下：

instance  Show Char  where
    showsPrec _ '\'' = showString "'\\''"
    showsPrec _ c    = showChar '\'' . showLitChar c . showChar '\''

    showList cs = showChar '"' . showl cs
                 where showl ""       s = showChar '"' s
                       showl ('"':xs) s = showString "\\\"" (showl xs s)
                       showl (x:xs)   s = showLitChar x (showl xs s)

putChar         :: Char -> IO ()
putChar c       =  hPutChar stdout c

parseTest函数在内部使用print函数，print函数本身在内部使用show，这就是为什么要获取delta的Unicode代码点值