Course of Raku / Functional, concurrent, reactive, and web programming / Reactive programming / await / Exercises / Await a failure

Solution: Await a failure

Here is a possible solution to the task.

Code

my $p = start { die 'boom' };

try {
    await $p;
    CATCH {
        default { say "caught: {.message}" }
    }
}

🦋 You can find the source code in the file await-failure.raku.

Output

caught: boom

Comments

1. The promise’s block throws, so the promise is broken. The exception is not lost — it is held until someone awaits the promise.

2. await $p rethrows it right there, where the CATCH phaser handles it like any ordinary exception. This is how errors in background work surface where you wait for the result.

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