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