Re: x, xx, and negative counts
On 29 May 2007, at 19:21, Mark J. Reed wrote:
My expectation before reading the delta was that negative counts
would do a reversal:
123 x -1 = 321
('a', 'b', 'c') xx -3 = ('c', 'b', 'a', 'c', 'b', 'a', 'c', 'b', 'a');
I don't know why I think that makes sense, but it was honestly my
first thought. Does it make sense to anyone else? Is there a
compelling reason I'm missing for having negative values behave as if
they were zero rather than adding some other potentially useful
functionality?
You're going to surprise people who use x to create padding strings
if a negative count produces a padding string of the same length.
--
Andy Armstrong, hexten.net
Re: x, xx, and negative counts
On Tue, May 29, 2007 at 02:21:37PM -0400, Mark J. Reed wrote:
: My expectation before reading the delta was that negative counts
: would do a reversal:
:
: 123 x -1 = 321
:
: ('a', 'b', 'c') xx -3 = ('c', 'b', 'a', 'c', 'b', 'a', 'c', 'b', 'a');
:
: I don't know why I think that makes sense, but it was honestly my
: first thought. Does it make sense to anyone else? Is there a
: compelling reason I'm missing for having negative values behave as if
: they were zero rather than adding some other potentially useful
: functionality?
The main rationale for going with null return is that the biggest use of
replication has generally been something like:
say $foo, ' ' x (20 - $foo.width), $bar
and it would be counterproductive to degrade to negative spaces in
such a case. (This is also the rationale for not returning failure
on negative counts.)
Note, however, that these are just multimethods, so if you defined a
variant that accepted a count of type Int where *..-1, it would come
earlier in the candidate list than the normal count of type Int.
So you could give it different semantics if you like.
Arguably, in Perl 6 people might instead write
say $foo.fmt(%20s), $bar
but just because people can write it that way doesn't mean they will.
(Plus that approach doesn't work if you want to count tabs.)
And generally, I think
@list xx -1
is less readable than
@list.reverse
so I don't feel inclined to include it as another Way To Do It.
Larry
Re: x, xx, and negative counts
On 5/29/07, Larry Wall [EMAIL PROTECTED] wrote: The main rationale for going with null return is that the biggest use of replication has generally been something like: say $foo, ' ' x (20 - $foo.width), $bar and it would be counterproductive to degrade to negative spaces in such a case. (This is also the rationale for not returning failure on negative counts.) OK. That makes sense. Thanks. And generally, I think @list xx -1 is less readable than @list.reverse so I don't feel inclined to include it as another Way To Do It. I wholeheartedly agree on the readability issue. Nor was I setting out to add a new Way To Do anything; it's just that my automatic expectation for what would happen (which I'm not trying to defend as particularly logical) was being violated, and P6 hasn't done that too often. So I prodded to see what was going on in @larry.brain. Your explanation is all I needed to shush the little grumbles in my head. Thanks again! -- Mark J. Reed [EMAIL PROTECTED]
Re: x, xx, and negative counts
On 5/29/07, Mark J. Reed [EMAIL PROTECTED] wrote:
My expectation before reading the delta was that negative counts
would do a reversal:
123 x -1 = 321
('a', 'b', 'c') xx -3 = ('c', 'b', 'a', 'c', 'b', 'a', 'c', 'b', 'a');
I don't know why I think that makes sense, but it was honestly my
first thought. Does it make sense to anyone else? Is there a
compelling reason I'm missing for having negative values behave as if
they were zero rather than adding some other potentially useful
functionality?
snip
In Perl 5 I commonly say things like
sub zeropad (
my ($len, $s) = @_;
my $slen = length $s;
carp the string $s is longer than the specified length $len if
$slen $len;
return = 0 x ($len - length($str)) . $str;
);
Which is roughly equivalent to doing a sprintf with the format %0${len}d.
