Macro yap::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. Return the first not-None result.

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");

If an expression returns None, no tokens will be consumed:

use yap::{ Tokens, IntoTokens };

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

let res: Option<()> = yap::one_of!(ts from &mut tokens;
    // This explicit iteration will be rewound if None is returned:
    { ts.next(); ts.next(); None },
);

assert_eq!(tokens.remaining(), "hello world");