Course of Raku / Advanced / Control flow / given and when / Exercises / Life stage from age

Solution: Life stage from age

Here is a possible solution to the task.

Code

my $age = 30;

given $age {
    when $_ < 0 { say 'invalid' }
    when 0..12  { say 'child' }
    when 13..19 { say 'teenager' }
    when 20..64 { say 'adult' }
    default     { say 'senior' }
}

🦋 You can find the source code in the file grade-the-score.raku.

Output

adult

Comments

1. This solution mixes two kinds of when. The first is a condition, $_ < 0 (where $_ is the topic set by given), which weeds out invalid ages; the rest are ranges that group the valid ages into stages.

2. Order matters. The negative-age guard comes first, so it runs before any range is tried. The value 30 falls into 20..64, so the program prints adult.

3. The default block covers every age of 65 and above, which is not captured by any of the listed ranges.

You could turn this around and let default catch the invalid input instead. List every recognised stage — including senior as the condition $_ >= 65 — and treat anything left over (such as a negative age) as invalid:

given $age {
    when 0..12    { say 'child' }
    when 13..19   { say 'teenager' }
    when 20..64   { say 'adult' }
    when $_ >= 65 { say 'senior' }
    default       { say 'invalid' }
}

Here default is a genuine “none of the above” branch. Which version reads better is a matter of taste: put the guard first when the invalid case is the exception, or make it the fallback when the valid stages are all clearly enumerated.

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