:: Ord a => [a] -> [a] -package:ghc -package:witherable -package:base -package:containers -package:safe -package:lifted-base -package:extra package:parsers -is:exact

try :: Parsing m => m a -> m a
parsers Text.Parser.Combinators
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.