Course of Raku / Functional, concurrent, reactive, and web programming / Concurrent programming / Promises / Exercises / Chain a promise

Solution: Chain a promise

Here is a possible solution to the task.

Code

my $p = start { 'raku' };
my $q = $p.then({ .result.uc });
my $r = $q.then({ .result ~ '!' });
say await $r;

🦋 You can find the source code in the file promise-result.raku.

Output

RAKU!

Comments

Each .then builds a new promise that runs once the previous one is done. Inside its block, .result is the value the previous promise produced.
The first follow-up upper-cases 'raku' into 'RAKU'; the second appends '!'. Awaiting the last promise, $r, walks the whole chain and yields 'RAKU!' — a small pipeline where each step transforms the result of the step before it.

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