This is the nature of the execution flow of perl - my @r hasn't been 'executed' yet, so you'll want something along the lines of a BEGIN block if you want it to be initialized and have it after the subroutine call e.g

foo();

BEGIN {
  my $str = 'a string';
  sub foo { print "\$str is $str\n" }
}

__output__

$str is a string
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