[Haskell-cafe] A simple attoparsec question

Robert Clausecker fuzxxl at gmail.com
Tue Mar 1 22:15:38 CET 2011

Hi Haskellers!

I'm currently trying to write an assembler for Knuths MMIXAL language.
Currently, I'm writing the parser using attoparsec, and have one

In MMIXAL, a string literal starts with a ", followed by an arbitrary
amount of arbitrary characters excluding the newline character and
finished with another ". For example: "Hello, World!" is a string, "ſ"
is a string too, but "\n" (\n is a newline) isn't. Here's the parser,
which parses a s tring and other kinds of constants:

  parseConstant = Reference <$> try parseLocLabel
              <|> PlainNum <$> decimal
              <|> char '#' *> fmap PlainNum hexadecimal
              <|> char '\'' *> (CharLit <$> notChar '\n') <* char '\''
              <|> try $ (char '"' *> (StringLit . B.pack <$>
                    manyTill (notChar '\n') (char '"')))
              <?> "constant"

The problem is, that attoparsec just silently fails on this kind of
strings and tries other parsers afterwards, which leads to strange
results. Is there a way to force the whole parser to fail, even if
there's an alternative parser afterwards?

I hope, you understand my question.

Yours, Robert Clausecker
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