:: Ord a => [a] -> [a] -package:html-entities -package:incipit-base -package:lens -package:statistics -package:safe -is:exact -is:exact -package:lifted-base -package:errors -package:integration -package:extra 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.