:: Ord a => [a] -> [a] -package:html-entities -package:basement -is:exact -package:base -package:lens -package:safe -package:extra -is:exact -package:errors -package:imports -package:Cabal-syntax -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.