Monadic parseOnly

[zudov]

Often it's necessary to run a parser inside another parser. It's usually done with something like this:

captureAndParse = do
    raw <- capture
    case parseOnly parse raw where
        Left err -> fail err
        Right res -> return res 

It would be nice to have a function parseOnlyM which runs a parser and calls fail on Left result. It can be implemented in this way:

parseOnlyM :: Monad m => Parser a -> Text -> m a
parseOnlyM parser input = either fail return $ parseOnly parser input

Which would allow to simplify the first example to following:

captureAndParse = capture >>= parseOnlyM parse

What do you think about such addition? I would be happy to make a PR.

[solatis]

Perhaps what we're really looking for here is a combinator that wraps this ? It looks like a pattern that should be captured (pun intended :)) on a higher level.

[bos]

fail is definitely not the right function to be using here, sorry.