:: Ord a => [a] -> [a] -package:list-t -package:base-prelude -package:ghc -is:exact -package:containers -package:extra -package:incipit-base -package:errors -package:base -package:lens -package:hxt -package:lifted-base 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.