Parser for Quoted string using Parsec

Question

I want to parse input strings like this: "this is \"test \" message \"sample\" text"

Now, I wrote a parser for parsing individual text without any quotes:

parseString :: Parser String
parseString = do
  char '"'
  x <- (many $ noneOf "\"")
  char '"'
  return x

This parses simple strings like this: "test message"

Then I wrote a parser for quoted strings:

quotedString :: Parser String
quotedString = do
  initial <- string "\\\""
  x <- many $ noneOf "\\\"" 
  end <- string "\\\""
  return $ initial ++ x ++ end

This parsers for strings like this: \"test message\"

Is there a way that I can combine both the parsers so that I obtain my desired objective ? What exactly is the idomatic way to tackle this problem ?

Answer 1

This is what I would do:

escape :: Parser String
escape = do
    d <- char '\\'
    c <- oneOf "\\\"0nrvtbf" -- all the characters which can be escaped
    return [d, c]

nonEscape :: Parser Char
nonEscape = noneOf "\\\"\0\n\r\v\t\b\f"

character :: Parser String
character = fmap return nonEscape <|> escape

parseString :: Parser String
parseString = do
    char '"'
    strings <- many character
    char '"'
    return $ concat strings

Now all you need to do is call it:

parse parseString "test" "\"this is \\\"test \\\" message \\\"sample\\\" text\""

Parser combinators are a bit difficult to understand at first, but once you get the hang of it they are easier than writing BNF grammars.