I didn't realise that the function vs. variable "declaration" happens in different stages.

Function and variable declarations both happen at compile time. You wouldn't have been able to compile the function if that wasn't the case. How can it use a variable that doesn't exist?

Assignments, on the other hand, happen at run-time. That's why the following code works:

>perl -E"for (qw( a b )) { my $x = $_; say $x }"
a
b
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