:: Ord a => [a] -> [a] -package:list-t is:exact -package:incipit-base -package:vector-algorithms -package:Cabal-syntax -package:Cabal -package:safe -package:mono-traversable -package:statistics -package:lens -package:base -package:extra 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.