:: Ord a => [a] -> [a] -package:hspec -package:Cabal -package:safe -package:vector-algorithms -package:statistics -package:Cabal-syntax -package:mono-traversable -is:exact -package:witherable -package:hedgehog -package:ghc 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.