Course of Raku / Objects, I/O, and exceptions / Exceptions / Soft failures / Exercises / Lookup or not found

Solution: Lookup or not found

Here is a possible solution to the task.

Code

sub lookup($key) {
    fail 'no such key' if $key ne 'a';
    return 100;
}

my $r = lookup('z');
if $r.defined {
    say $r;
}
else {
    say 'not found';
    say "reason: {$r.exception.message}";
}

🦋 You can find the source code in the file lookup.raku.

Output

not found
reason: no such key

Comments

1. lookup('z') calls fail, so it returns an undefined Failure.

2. Because the result is undefined, the program prints not found rather than trying to use the failed value.

3. A Failure still carries the exception that describes what went wrong. $r.exception retrieves it — which also marks the failure as handled, so it will not blow up later — and .message reads the text passed to fail, no such key.

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