:: Ord a => [a] -> [a] -package:statistics -package:witherable -package:errors -package:imports -package:extra -package:basement -package:base-prelude -package:mono-traversable -package:ghc -package:hxt 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.