如何用“。”分隔字符串 在Haskell中，但是如果周期在两个数字之间，例如：（2.5），则不拆分？

您可以通过多种方法来执行此操作。这是一些。

与Text.Regex：

import Text.Regex.TDFA -- I think this will work with the other regex backends too

getAllTextMatches ("One. Two. a 3.5 b. cde." =~ "([0-9]\\.[0-9]|[^.])+" :: AllTextMatches [] String)
-- ["One"," Two"," a 3.5 b"," cde"]

使用Text.ParserCombinators.ReadP（在中base，因此不需要第三方库）：

import Data.Char
import Text.ParserCombinators.ReadP

parseDigitsWithDecimalPoint = (\a b c -> [a,b,c]) <$> satisfy isDigit <*> char '.' <*> satisfy isDigit
parseNonDot = (:[]) <$> satisfy ('.' /=)
parseSentence = fmap concat . many $ parseDigitsWithDecimalPoint <++ parseNonDot
readP_to_S (sepBy parseSentence (char '.') <* eof) "One. Two. a 3.5 b. cde."
-- [(["One"," Two"," a 3.5 b"," cde",""],"")]

与Text.Regex.Applicative：

import Control.Applicative.Combinators
import Data.Char
import Text.Regex.Applicative

parseDigitsWithDecimalPoint = (\a b c -> [a,b,c]) <$> psym isDigit <*> sym '.' <*> psym isDigit
parseNonDot = (:[]) <$> psym ('.' /=)
parseSentence = fmap concat . many $ parseDigitsWithDecimalPoint <|> parseNonDot
match (sepBy parseSentence (sym '.')) "One. Two. a 3.5 b. cde."
-- Just ["One"," Two"," a 3.5 b"," cde",""]

与Text.Megaparsec：

{-# LANGUAGE FlexibleContexts, TypeFamilies #-}
import Data.Char
import Text.Megaparsec

parseDigitsWithDecimalPoint = (\a b c -> [a,b,c]) <$> satisfy isDigit <*> single '.' <*> satisfy isDigit
parseNonDot = (:[]) <$> anySingleBut '.'
parseSentence = fmap concat . many $ try parseDigitsWithDecimalPoint <|> parseNonDot
parseMaybe (sepBy parseSentence (single '.')) "One. Two. a 3.5 b. cde."
-- Just ["One"," Two"," a 3.5 b"," cde",""]

完全手工完成：

import Data.Char
import Data.List.NonEmpty

foo = go id where
  go f "" = f "" :| []
  go f ('.':xs) = f "" <| go id xs
  go f (x1:'.':x2:xs) | isDigit x1 && isDigit x2 = go (f . (x1:) . ('.':) . (x2:)) xs
  go f (x:xs) = go (f . (x:)) xs
foo "One. Two. a 3.5 b. cde."
-- "One" :| [" Two"," a 3.5 b"," cde",""]