:: Ord a => [a] -> [a] -package:list-t -package:extra -package:ghc -package:statistics -package:incipit-base -package:vector-algorithms -package:lens -package:Cabal -package:errors is:exact -package:generic-deriving -package:integration 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.