:: Ord a => [a] -> [a] -package:stm-containers -package:safe -package:Cabal -package:extra -package:incipit-base -package:lifted-base -package:Cabal-syntax -is:exact -package:base-prelude -package:statistics -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.