:: Ord a => [a] -> [a] -package:html-entities -package:safe -is:exact -is:exact -package:errors -package:mono-traversable -package:Cabal-syntax -package:ghc -package:lens -package:base-prelude -package:extra is:exact 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.