:: Ord a => [a] -> [a] is:exact -package:ghc -package:imports -package:extra -package:witherable -package:containers -package:base-prelude -package:basement -package:hxt -package:mono-traversable -package:hedgehog -package:generic-deriving 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.