Macro try_flow

macro_rules! try_flow {
    (log $n:ident: $x:expr) => { ... };
    ($x:expr) => { ... };
}

Breaks the control-flow if the block returns a value for which ConsumedEvent::is_consumed is true.

It does the classic into()-conversion and returns the result.

The difference to flow is that this one Ok-wraps the result.

Extras: If you add a marker as in try_flow!(log ident: {...}); the result of the operation is written to the log.