Errata

http://tpj.com/tpj.com/tpj/contest

should read

http://tpj.com/tpj/contest

http://www.ioccc.org/

The Perl Journal's Obfuscated Perl Contest URL has a duplicate "tpj.com", but
there seem to be other problems. It *appears* to now be at

http://fahrenheit-451.media.mit.edu/tpj/contest/

The cd-command should end in "advanced_perl", not "advanced.perl", shouldn't
it?

I tested it on AIX and perl5.004_01.

- The BEGIN block does not work as expected. It seems that $blocking_supported
in this block is some other value as the my $blocking_supported = 0; defined
in the program. I also don't understand this, (it should work ??)

- The function calls $conn->set_non_blocking(), $conn->set_blocking() will
not work as intended; in these functions fcntl is called with the hash
reference. It should be:

fcntl($_[0]->{sock} , ...

- On AIX when syswrite blocks, $! will be set to "Resource temporarily
unavailable" instead of EAGAIN. So _err_will_block() will not work as expected.
This is not a bug of course but a machine dependency.

{example archive} There are a couple of things in the tetris.pl example which
are in the examples archive for Advanced Perl Programming that don't seem to
work quite right.

My perl : 5.005_02
My Tk.pm : Tk800.012

At line 482 (the first statement in sub create_screen{}), the program as
shipped does:

$w_top= MainWindow->new('Tetris - Perl/Tk') ;

which dies with

"Odd number of argsMainWindow->new(Tetris - Perl/Tk)"

This one can be fixed by:

$w_top = MainWindow->new() ;
$w_top->title('Tetris - Perl/Tk') ;


The second one is little more subtle. On line 154, the comparison "$new_col >
$MAX_COLS" isn't right--there *are* ten columns, but they're numbered starting
from zero. You can demonstrate the problem with this by moving pieces to the
right edge and rotating them. Depending on the shape of the piece, you can
get the piece to run off the edge of the playfield and stick.

To fix this, all you have to do is change the comparison to:

($new_col >= $MAX_COLS)

{EXAMPLES}
ftp://ftp.oreilly.com/published/oreilly/nutshell/advanced_perl/examples.tar.gz

The file "examples/Jeeves/lib/Ast.pm":

sub get_prop_value {
my ($this, $prop_name) = $_[0];
return $this->{$prop_name};
}

should be

sub get_prop_value {
my ($this, $prop_name) = @_;
return $this->{$prop_name};
}

Tetris Bug Fix:

Bug = when object is on the right
wall and you rotate - the object can be frozen before it hits bottom and
the object will partially go outside the right boundry.

sub rotate {
# rotates the block counter_clockwise
return if (!@cells);
my $cell;
# Calculate the pivot position around which to turn
# The pivot is at (average x, average y) of all cells
my $row_total = 0; my $col_total = 0;
my ($row, $col);
my @cols = map {$_ % $MAX_COLS} @cells;
my @rows = map {int($_ / $MAX_COLS)} @cells;
foreach (0 .. $#cols) {
$row_total += $rows[$_];
$col_total += $cols[$_];
}
my $pivot_row = int ($row_total / @cols + 0.5); # pivot row
my $pivot_col = int ($col_total / @cols + 0.5); # pivot col
# To position each cell counter_clockwise, we need to do a small
# transformation. A row offset from the pivot becomes an equivalent
# column offset, and a column offset becomes a negative row offset.
my @new_cells = ();
my @new_rows = ();
my @new_cols = ();
my ($new_row, $new_col);
while (@rows) {
$row = shift @rows;
$col = shift @cols;
# Calculate new $row and $col
$new_col = $pivot_col + ($row - $pivot_row);
$new_row = $pivot_row - ($col - $pivot_col);
$cell = $new_row * $MAX_COLS + $new_col;
# Check if the new row and col are invalid (is outside or
#something
# is already occupying that cell)
# If valid, then no-one should be occupying it.
if (($new_row < 0) || ($new_row > $MAX_ROWS) ||
($new_col < 0) || ($new_col > $MAX_COLS -1 ) ||
$heap[$cell]) {
return 0;
}
push (@new_rows, $new_row);
push (@new_cols, $new_col);
push (@new_cells, $cell);
}
# Move the UI tiles to the appropriate coordinates
my $i= @new_rows-1;
while ($i >= 0) {
$new_row = $new_rows[$i];
$new_col = $new_cols[$i];
$w_heap->coords($tile_ids[$i],
$new_col * $TILE_WIDTH, #x0
$new_row * $TILE_HEIGHT, #y0
($new_col+1) * $TILE_WIDTH, #x1
($new_row+1) * $TILE_HEIGHT);
$i--;
}
@cells = @new_cells;
1; # Success
}

Apostrophes around /bin/rm * should be back ticks.

last line of C shaded box on left side of diagram should read

} foo = {10, "good" };

push (@{$matrix_name}, @row;) # insert the row-array into

should read

push (@{$matrix_name}, @row); # insert the row-array into

The sample data files on 28 list student Garibaldi as id 52003; the sample
code on 29 lists Garibaldi as id 42343.

The example student structure doesn't list any courses, but the following text
discusses foreign keys versus references as though courses were listed in the
sample. The text also refers to HS201 as a course taken by Garibaldi; in
fact, it's listed in the data files as a course taught by Schumacher and not
taken by Garibaldi.

The file F is opened but is not closed.

/(A-Za-z]+).*(d+)-(d+)/

This won't work for Starting-Hours >= 10, because the .* in front of the first
(d+) will get the first digit. The d+ will only get the second digit. Make
.* non-greedy (.*?) or change it to [^0-9]* to prevent it from "eating" digits.

course_get_hours: sub course_get_hours{...} is missing.

... $course_taught
";

should be

... $r1_courses->[$i]
";

The line "$to = 19 if $to == 7;" is not needed. It is handled by the next line
that tests for $to <= 7.

What you have:
for $j ($i+1 .. etc.)
What it should be:
foreach $j ($i+1 .. etc.)

There is no variable

$course_taught

even through is it referenced in this print statement. Should be

$r_courses->[$i].

die "..." should terminate with $! instead of $:.

} elseif ($ref_type eq "SCALAR") {

should read

} elsif ($ref_type =~ /SCALAR/) {

Example 14-4 does not, as stated, invoke the "cascade" method.

comment should be: # Prints "Batman and Robin
"

comment should read: # prints "foo called
"

I could not get the reference call to the "default" subroutine to work in the
dispatch table example:

&{$rhOptions{"_default_"}};

Nor could I get the reader's (unofficial) correction to work.

Copying the example code given in the book's code a block above the
aforementioned line did, however, work:

i.e.

else {
if(exists $rhOptions->{"_default_"}) {
$rsub = $rhOptions->{_default_};
&$rsub();
}
}

print $random_iter1(), " ", $random_iter2(), "
"

should be

print $random_iter1->(), " ", $random_iter2->(), "
"

or

print &$random_iter1(), " ", &$random_iter2(), "
"

Lines 1 and 2 of the figure should be swapped to match the code on page 67.

It says:

"If @patterns contains the three strings "^abc", "ghi", "efg$",
for example, the code supplied to eval looks like this:

while (<>) {if (/^foo/ && /bar$/ && /ghi/) {print $_;}}"

The Perl code line should read:

"while (<>) {if (/^abc/ && /ghi/ && /efg$/) {print $_;}}"

$tmp .= " " x (7 - length($tmp));

extends $tmp to its size of 7 characters. Of course, that is only necessary if
$tmp might be shorter than 7 characters. But that is impossible, as $s is
extended (in line 9) enough to guarantee the length of 7 characters for $tmp.

The same applies to lines 13/15 and to the generating sourcecode on page 79.

the www links and papers by Don Pardo:

http://www.cs.washington.edu/homes/pardo/rtcg.d/index.html
should be ...
http://www.cs.washington.edu/research/compiler/rtcg.html

"Perl first looks for the file given to use() or require()
in the current directory and then looks up the @INC built-in
array to search the include paths."

This sentence is incorrect. Perl searches for used or require'd files in @INC.
By default, the current directory is in @INC, but it is at the end, so it is
searched *after* all the other paths in @INC.

"The double colon gets translated to a filename separator,
because the colon has a special significance for DOS
filenames."

Well...no. The double colon gets translated to a filename separator so that
the package name becomes a valid path. Consider:

OS Package -> Path
Unix Foo::Bar -> Foo/Bar.pm
DOS Foo::Bar -> FooBar.pm

Saying that the double colon is translated in order to accommodate DOS
misapprehends both the translation mechanism and the history of Perl, which
was originally developed for Unix, not DOS.

The entries "hours_worked" and "overtime_hours_worked" are being used in
"compute_ytd_income," but are nowhere defined.

indirect notation. See the Camel book, p295.

"allocate uses this to bless the object directly into
the inherited class."

Derived classes "inherit" things from base classes. You can reasonably say
that a derived classes "inherits" its base class. But even granting some abuse
of notation, it is wrong to refer to a derived class as the "inherited" class.

This is particularly unfortunate in this paragraph, because it is essential
that the user clearly understand the inheritance relationships in order to
understand why allocate() shouldn't hardcode the class name.

The sentence might be better written as

"allocate uses this to bless the object directly into
the HourlyEmployee class."

want to rely on my own scant Perl knowledge. -efm)

use StoreItem;

before

@ISA = qw(StoreItem);

comp.object FAQ. The URL given brings one to an empty directory; it appears
that comp.object no longer has a FAQL.

comp.object FAQ apparently is now archived at:

http://www.faqs.org/faqs/by-newsgroup/comp/comp.object.html

Delete line 4: "my (@retcal);".

data-structure in a way that uses an object in the class that you want to
inherit from. (That is, use containment.) Do not include that package in
@ISA. Use an AUTOLOAD subroutine for unknown calls that passes the base
object to the class that you inherit from. BINGO! You have a module that
inherits an interface even if the base class changes.

with a:

my $obj = shift;
$obj->get_temp();

and the STORE:

my ($obj, $t) = @_;
$obj->set_temp($t);

At the moment there's a mix of $obj and $ac.

last if $last_index > $index;

Perhaps it should read

last if $last_index >= $index;

so it does not overshoot the line.

syswrite(F, $msg, length($msg)); # can also use write() or print()

This is bizarre and/or wrong. The ordinary way to code this is

print F $msg;

Using syswrite() might make the code run a bit faster, but it also invites
bugs from programmers who forget (or don't know) that mixing syswrite() and
print() is treacherous.

write() is for outputting formats: it won't work at all.

Is "B+Tree" correct? (Shouldn't the "+" be a "-"?)

$sth = $dbh->prepare('insert into emptable (name, age)
values (?, ?)');

and

$sth->execute($id, $name, $age);

These two lines seem inconsistent. There are 2 question marks in the prepare()
call, but 3 parameters in the execute() call.

$query =~ s/\[# Hopefully 200 and 201 aren't being
$query =~ s/\["]/201/g; # being used.

The first line is not correct. It should probably appear as follows:

$query =~ s/\[']/200/g; # Hopefully 200 and 201 aren't
$query =~ s/\["]/201/g; # being used.

$main_socket.

print "Server created. Waiting for events";

should be

print "Server created. Waiting for events.
";

$image = $label->Bitmap(file => 'face.xbm'); etc

Each of these lines must read

$image = $label->Bitmap(-file => 'face.xbm'); etc....

ie, must have a hyphen before the word "file" (also on the CD).

Change "explicitly using the add method" to "explicitly using the insert
method."

"[N$widget]" should be "[$widget]".

Basically, the named parameters to the hlist methods should all start with a
hyphen: "image =>" should be "-image =>", "text =>" should be "-text =>",
"imagetext" should be "-imagetext", etc.

} elsif ($line =~ /^s*@FOREACHs*(w*)s*(.*)s*/i {

The last s* is useless, because .* will "eat" all whitespace. Why not write
(w+) instead od (w*) to ensure that at least one word-char. is present?

Near the end of the example, there are these lines:

for (num = 1; num <= 7; num++) {
char buf[20];*buf = '';

that should be

for (num = 1; num <= 7; num++) {
char buf[20];
*buf = '';

I believe.

There are also a lot of tabs in code (that's how I found this) that should be
cleaned up.

The URL might need to be changed to:

"http://perl.apache.org/"

In Figure 20-2 I can see only one of the two mentioned pointers to "add's
children. But maybe I didn't understand it.

APP 1st edition (aug 97)

The listing for the fifth macro on page 330, table 20-1, reads as follows:

'sv_setpv (SV*, char *,
int len'

It is missing the terminating paren (and possibly a semi-colan).

An additional, though probably more stylistic inconsistancy is that only some of the listings in this
table are semi-colan terminated.

only produce useful output if you have DEBUGGING #DEFINED when you compile
Perl. If you do not have DEBUGGING defined, then the call will produce no
output.

"So if xhv_keys exceeds xhv_fill, Perl takes it ..."

xhv_fill should be xhv_max (source: perl-5.6.1/hv.c:423)

APP - first edition (aug. '97)

In the second code listing on page 355 (Ch 20, section 'The Called Side: Hand-Coding an XSUB, subsection
'Returning a variable list of results') has the following statement:

sv_setpv(ST(i), "hello", 0); /* Like modifying $_[i] */

I'm not certain of the error here, but this call is inconsistant with the definition given in table 20-1

In Appendix B, paragraph 22, the line

${"i"} = 10; # sets $foo to 10

should read either (most likely)

${"$i"} = 10; # sets $foo to 10

or (unlikely)

${"i"} = 10; # sets $i to 10