:: Ord a => [a] -> [a] -package:list-t -package:Cabal-syntax -package:safe -package:incipit-base -package:base -package:errors -package:mono-traversable -package:vector-algorithms -package:ghc -package:integration -package:vector package:parsers is:exact
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.