:: Ord a => [a] -> [a] -package:focus -package:imports -package:base-prelude -package:statistics -package:containers -package:ghc -package:safe -package:lifted-base -package:generic-deriving -package:errors package:parsers -is:exact
Take a parser that may consume input, and on failure, go back to where
we started and fail as if we didn't consume input.