:: Ord a => [a] -> [a] -package:statistics -package:ghc -package:imports -is:exact -package:lifted-base -package:Cabal -package:Cabal-syntax -package:vector -package:generic-deriving -package:base-prelude package:parsers is:exact
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.