:: Ord a => [a] -> [a] -package:focus -package:witherable -package:imports -package:base -package:safe -package:vector-algorithms -package:ghc -package:lifted-base -package:integration -package:Cabal-syntax -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.