在Haskell中解析字符（-）时出错

Question

I'm writing a parser to parse huge chunks of English text using attoparsec. Everything has been great so far, except for parsing this char "――" . I know it is just 2 dashes together "--" . The weird thing is, the parser catches it in this code:

wordSeparator :: Parser ()
wordSeparator = many1 (space <|> satisfy (inClass "――?!,:")) >> pure () 

but not in this case:

specialChars = ['――', '?', '!', ',', ':']
wordSeparator :: Parser ()
wordSeparator = many1 (space <|> satisfy (inClass specialChars)) >> pure ()

The reason I'm using the list specialChars is because I have a lot of characters to consider and I apply it multiple cases. And for the input consider: "I am ――Walt Whitman._" and the output is supposed to be {"I", "am", "Walt", "Whiteman."} I believe it's mostly because "――" is not a Char? How do I fix this?

Answer 1

A Char is one character, full stop. ―― is two characters, so it is two Char s. You can fit as many Char s as you want into a String , but you certainly cannot fit two Char s into one Char .

Since satisfy considers individual characters at a time, it probably isn't what you want if you need to parse a sequence of two characters as a single unit. The inClass function just produces a predicate on characters ( inClass partially applied to one argument produces a function of type Char -> Bool ), so inClass "――" is the same as inClass ['―', '―'] , which is just the same as inClass ['―'] since duplicates are irrelevant. That won't help you much.

Consider using string instead of or in combination with inClass , since it is designed to handle sequences of characters. For example, something like this might better suit your needs:

wordSeparator :: Parser ()
wordSeparator = many1 (space <|> string "――" <|> satisfy (inClass "?!,:")) >> pure ()