:: Ord a => [a] -> [a] -package:html-entities -package:incipit-base -package:basement -package:statistics -package:lens -package:extra -package:amazonka-core -package:safe -package:Cabal -package:Cabal-syntax -package:hxt -package:vector 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.