:: Ord a => [a] -> [a] -package:html-entities -package:extra -package:ghc -package:containers is:exact -package:integration -package:lens -package:Cabal -package:Cabal-syntax -package:base-prelude -package:hxt -package:lifted-base 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.