Why does the block use $^a in one place (the automatic parameter) and $a in another place? Shouldn't that be a different (undeclared) variable? (Likewise for b).

No, the ^ twigil is only necessary in the first occurrence. That was introduced because things like this:

my $block = {
      my $v = %hash{$^key};
      say "The lookup {%hash{$^key}} yields $v";
};
[download]

Would complain about the closure inside the string getting no argument, because $^key was interpreted as a formal parameter to the inner-most closure, which in this case was the one inside the string.

Or more general, you couldn't refer to outer lexicals that happened to be self-declaring formal parameters.

So it was decided that after $^foo occurred once, you could refer to it as $foo to, disambiguating it in inner blocks.

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.