Input in @a, output in $last[-1].

use Data::Dumper;
$Data::Dumper::Deepcopy = 1;

my @a = qw/foo bar baz/;
my @last = (1);
push @last, { $_ => $last[-1] } foreach reverse @a;
print Dumper( $last[-1] ); # result
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I use Data::Dumper just to print the output. It is not required to obtain the result. Output:

$VAR1 = {
          'foo' => {
                     'bar' => {
                                'baz' => 1
                              }
                   }
        };
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