Right. I'd like a no-copy combinator for the same reasons, but I think it's impossible to do without some low-level support.

 

Not very easily. Internally, attoparsec maintains just three pieces of data for its state:

• The current input
• Any input we received via continuations, in case we need to backtrack
• A flag that denotes whether we were fed EOF by a continuation

There are no line numbers, no "bytes consumed" counters, nothing else. If there was a "bytes consumed" counter, it would be possible to write a "try"-like combinator that would hold onto the current input, run a parser, tack on any input received via continuations to the original input, and then use the counter to slice off a portion of that bytestring without copying. I can't think of another way to do it. Adding that counter would be a moderate amount of work, and would presumably have a negative effect on performance.