Sonic Spin

Declares a macro that turns the ::() postfix operator into a general postfix operator.
Mostly by re-defining structures from the syn for parsing.

Example

#![feature(proc_macro_hygiene)]
use sonic_spin::sonic_spin;

sonic_spin! {
    let res = 0::(match) {
        x => x + 2
    }::(match)  {
        x => x + 10
    };
    assert_eq!(res, 12);


    let mut acc = 0;
    (0..3)::(for _ in) {
        acc += 1;
    };
    assert_eq!(acc, 3);
}

See tests/ for further examples.

Motivation

Given some of the many discussions regarding the await syntax and the resulting possibility of general postfix operators, this crate explores such possibility with the "sonic-spin" operator (::()).
If the await syntax turned out to be "prefix await" await expr, then this crate would enable the syntax expr::(await) similarly to the ? postfix operator.

Some of the mentioned discussions:

• https://internals.rust-lang.org/t/idea-universal-pipelining-a-k-a-making-await-generic/9973

• https://github.com/rust-lang/rfcs/pull/2442

Further work

• Explore if/how postfix macros could work.
• Test with the await case (even if it's already a postfix operator).
• Explore auto bracing addition.

Pipe operations

For piped operations, see the tests/common.rs::Pipe trait and it's usage in tests/if.rs::if_pipe function. ie. sonic-spin is not required for such operations.

Notes

This is a draft and is based on this suggestion:
https://github.com/rust-lang/rfcs/issues/2698