:: Ord a => [a] -> [a] -package:witherable -package:extra -package:ghc is:exact -package:lifted-base -package:containers -package:base -package:lens -package:Cabal-syntax -package:base-prelude -package:Cabal 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.