In that case, the question was "How do I get the output format I want?" This is a case of "Why doesn't Perl interpolate hashes in strings?" I only shamelessly plug my previous posts when it's justified.

Of course, with the right syntax, Perl will interpolate anything in a string.

my %hash = ( foo => 1, bar => 2, baz => 3 );
print "@{[%hash]}";
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But here's another reducing scheme that doesn't involve strenuous exercise or counting calories:

print((reduce { $a . ($$...$$ ? ' => ' : ',') . $b } %hash), $/);
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The flip-flop doesn't maintain state between calls because in this case, it's not the same flip-flop on each call! Each entry into a subroutine gets a "different" flip-flop.