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From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: More ** weirdness
Message-ID: <109199@convex.convex.com>
Date: 24 Nov 90 02:38:04 GMT
References: <109161@convex.convex.com> <9077@cognos.UUCP>
Sender: news@convex.com
Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
Lines: 37

In article <9077@cognos.UUCP> alanm@cognos.UUCP (Alan Myrvold) writes:
> (quoting a posting of mine)
>well for me (on a Sun), it is exactly opposite (as I would expect).

You're right -- I got the signs switched.  Sorry.  What I wanted to know
was why the Sun version seemed to be able to take the log of a negative
number, and moreover do the right thing.  I always expected perl to be
checking first to make sure it never called the log of a negative number,
and remembering to restore the sign on odd integral exponents.

>What surprises me is the need for parentheses when using '**' with 'print'.  
>On both PL 36 and 41,

That's because it looked like a function to perl.  The list operators
(like print, unlink, sort, chown, ...) are peculiar creatures at best.
They normally gobble up all their operands, as in
	func x, b, c, d;
but if they see a paren as the first token, they consider it the start 
of the argument list.  Because they're lowest in precedence (kind of),
	func x op y;	#	 like func(x op y);
	func(x) op y;	#	 like func(x) op y;
	func (x) op y;	#	 like func(x) op y;
It's that last case that bites you.  It may make some sense if you let
func==rand, but when func==print and op==+ or the like, it's a surprise
that 
	print  -2  + 2;
	print (-2) + 2;
should do such different things.  It's also when what you thought was a 
list separating comma becomes a scalar arithmetic comma and throws 
always returns the value of its RHS operand.  So beware that
    print i+2,3,4,5;	#	like print(i+2,3,4,5);
and
    print (i+2),3,4,5;	#	like print(i+2),3,4,5;
are different.


--tom