:: Ord a => [a] -> [a] -package:html-entities -package:statistics -package:extra -package:Cabal-syntax -is:exact -package:integration -package:basement -package:Cabal -package:ghc -package:safe -package:containers 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.