Question

我尝试使用关键字之间的一系列数据解析以下文本文件：

many text many text  many text 

BEGIN
T   LISTE2
1   154
2   321
3   519
4   520
5   529
6   426
END

many text  many text  many text

使用以下haskell程序

import Text.Parsec
import Text.Parsec.String
import Text.Parsec.Char
import Text.Parsec.Combinator

endOfLine :: Parser String
endOfLine =     try (string "\n") 
            <|> try (string "\r\n") 

line = many $ noneOf "\n"

parseListing = do 
  spaces
  many $ noneOf "\n"
  spaces
  cont <- between (string "BEGIN\n") (string "END\n") $ endBy line endOfLine
  spaces
  many $ noneOf "\n"
  spaces
  eof
  return cont

main :: IO ()
main = do
    file <- readFile ("test_list.txt")
    case parse parseListing "(stdin)" file of
            Left err -> do putStrLn "!!! Error !!!"
                           print err
            Right resu -> do  putStrLn $  concat resu

当我解析我的文本文件时，我收到以下错误：

"(stdin)" (line 16, column 1):
unexpected end of input
expecting "\n", "\r\n" or "END\n"

我是解析新手，我不明白为什么会失败？我的序列介于BEGIN和END

之间

您知道我的解析器有什么问题以及如何纠正它吗？

Answer 1

between永远不会停止，因为endBy line endOfLine也消耗任何行和END\n，因此它会消耗越来越多的行，直到失败为止。然后你的解析器会尝试使用string "END\n"并且也会失败，这就是错误消息提到"END\n"的原因您必须在END\n上重写行解析器以使其失败。例如：

parseListing :: Parsec String () [String]
parseListing = do 
    spaces
    many $ noneOf "\n"
    spaces
    cont <- between begin end $ endBy (notFollowedBy end >> line) endOfLine
    spaces
    many $ noneOf "\n"
    spaces
    eof
    return cont
    where
        begin = string "BEGIN\n"
        end = string "END\n"

使用Parsec意外结束输入

1 个答案: