Hi, Robert Clausecker wrote:

Each instruction has up to three operands, looking like this:

@+4 (Jump for bytes forward) "foo" (the string foo" '0'>>(1+2)

etc. A string literal may contain anything but a newline, (there are no escape codes or similar). But when I add a check for a newline, the parser just fails and the next one is tried. This is undesired, as I want to return an error like "unexpected newline" instead. How is this handled in other parsers?

I would expect that the other parsers are tried, but fail, because they do not accept an initial quotation mark. You get two errors messages then: 1. Unexpected newline after quotation mark 2. Unexpected quotation mark These two error messages reflect the two ways to solve the problem: Either delete the first quotation mark, or add a second one. Tillmann PS. Please use "Reply" to answer posts, so that they can be put into the same thread.

Apologies if this has been answered already (I've got a bit lost with this thread), but the *try* here seems to be giving you precisely the behaviour you don't want. *try* means backtrack on failure, and try the next parser. So if you want ill formed strings to throw an error if they aren't properly enclosed in double quotes don't use try. <|> try $ (char '"' *> (StringLit . B.pack <$> manyTill (notChar '\n') (char '"')))