:: Ord a => [a] -> [a] -package:list-t -package:base-prelude -package:basement -package:statistics -package:extra -package:base -is:exact -is:exact -package:lifted-base -package:ghc -package:lens -package:hxt package:parsers
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.