Function parser_combinators::token

pub fn token<I>(c: I::Item) -> Token<I> where
    I: Stream,
    I::Item: PartialEq, 

Parses a character and succeeds if the characther is equal to c

 let result = token('!')
     .parse("!")
     .map(|x| x.0);
 assert_eq!(result, Ok('!'));