is

mech_syntax::parser

Function is 

Source 
pub fn is<'a, F, O>(
    parser: F,
) -> impl FnMut(ParseString<'a>) -> ParseResult<'_, O>
where
    F: FnMut(ParseString<'a>) -> ParseResult<'_, O>,
Expand description

For parser p, return the !!p peek parsing expression.