How about exploiting that two numbers have the same sign when their product is positive?

sub same_sign {
    $_[0]*$_[1] > 0
};
[download]

The above version will treat 0 as a singularity which never has the same sign with anything, not even with itself. If you don't want that, you can make 0 have the same sign as a positive and a negative number:

sub same_sign {
    $_[0]*$_[1] >= 0
};
[download]

... but you can't say "0 is always positive" or "0 always is negative" with my method.

Update: After thinking about it a bit, I think the <=>-trick is the following:

sub same_sign {
   ($_[0] <=> 0) == ($_[1] <=> 0)
};
[download]

because shift <=> 0 is the sign function. It has different properties again - 0 has no sign, and compares as the same sign as 0, but it's different from any positive and any negative number.

---

---

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.