:: Ord a => [a] -> [a] is:exact -package:Glob -package:basement -package:statistics -package:vector-algorithms -package:witherable -package:base-prelude -package:ghc -package:lifted-base -package:lens -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.