Macro one_of 

macro_rules! one_of {
    ($tokens:ident; $( $e:expr ),+ $(,)?) => { ... };
    ($alias:ident from $tokens:expr; $( $e:expr ),+ $(,)?) => { ... };
}

Pass the provided tokens into each expression, one after the other. All of the expressions provided must return something implementing [crate::one_of::IsMatch], ie Option<T> or bool. It will try each expression until a match is found, consuming no tokens for any expressions that to not match.

• If expressions return Option<T>, then Some(T) denotes that we’ve found a match and can return it, and None means that one_of should try the next expression.
• If expressions return bool, then returning true denotes that we’ve found a match and returning false means to try the next expression.

Examples

A basic example:

use yap::{ Tokens, IntoTokens };

let mut tokens = "hello world".into_tokens();

// The macro expects a mutable reference to your tokens:
let ts = &mut tokens;
let res = yap::one_of!(ts;
    ts.tokens("bye".chars()).then(|| 1),
    ts.tokens("hi".chars()).then(|| 2),
    ts.tokens("hello".chars()).then(|| 3),
    ts.tokens("world".chars()).then(|| 4),
);

assert_eq!(res, Some(3));
assert_eq!(tokens.remaining(), " world");

You can declare an alias from some expression that’s passed in, too. Handy for abbreviating, or in this case, adding the required mut reference:

use yap::{ Tokens, IntoTokens };

let mut tokens = "hello world".into_tokens();

let res = yap::one_of!(ts from &mut tokens;
    ts.tokens("bye".chars()).then(|| 1),
    ts.tokens("hi".chars()).then(|| 2),
    ts.tokens("hello".chars()).then(|| 3),
    ts.tokens("world".chars()).then(|| 4),
);

assert_eq!(res, Some(3));
assert_eq!(tokens.remaining(), " world");

We can return bools too, for when we want to find out whether something matches but don’t care what exactly has been matched:

use yap::{ Tokens, IntoTokens };

let mut tokens = "hello world".into_tokens();

let res: bool = yap::one_of!(ts from &mut tokens;
    ts.tokens("howdy".chars()),
    ts.tokens("bye".chars()),
    ts.tokens("hello".chars()),
);

assert_eq!(res, true);
assert_eq!(tokens.remaining(), " world");

Expressions can return Results inside the Option too (or anything else that they wish), allowing for parsers to propagate errors out through this macro however you prefer.