Extracting line / column numbers from a failed parse

[statusfailed]

Is it possible to get the position of an error from a failed parse? I see that "Result" is either

Success a    
Failure Doc

But it doesn't seem like I'd be able to extract the line number from the Doc
The docs for Err also indicate that position isn't included, but not the reason why.

Is there a way to get this information?

[statusfailed]

So I've got the workings of a patch for this: https://github.com/statusfailed/trifecta/tree/failed-parse-locations

It works OK (although I'm not sure if there are any bugs - I basically just changed some types and fixed errors until it compiled). here's an example of what output you get:

GHCi> parseString (liftM2 (,) stringLiteral natural) mempty "\"Hi there\"\n\nBADPARSE" :: Result (String, Integer)
Failure (ErrInfo {_errDoc = (interactive):3:1: error: expected: natural
BADPARSE<EOF> 
^             , _errDeltas = [Lines 2 0 12 0]})

Unfortunately I've had to change the "Result" type, which breaks backwards compatibility. I'm not sure what the minimally-breaking way to write this would be - maybe add some IntermediateResult type which can be used to build a Result by the existing functions (parseString, parseByteString, etc.).
Then I could add more (different) parse functions, like "parseStringWithLocations".

@ekmett any thoughts?

[ekmett]

We need to change the Result and error types a bit anyways to support a race combinator, so I expect a non-backwards compatible release eventually anyways. =)

Put that into a pull request, and I can merge it, forcing me to remember to deal with this when I fix race.

[statusfailed]

Will do, but it's pretty messy! Let me know if you've any preferences for tidying before merging!