1 package Attribute::Handlers;
10 my ($pkg, $ref, $type) = @_;
11 return $symcache{$pkg,$ref} if $symcache{$pkg,$ref};
14 foreach my $sym ( values %{$pkg."::"} ) {
15 return $symcache{$pkg,$ref} = \$sym
16 if *{$sym}{$type} && *{$sym}{$type} == $ref;
21 VAR => [qw[SCALAR ARRAY HASH]],
22 ANY => [qw[SCALAR ARRAY HASH CODE]],
23 "" => [qw[SCALAR ARRAY HASH CODE]],
24 SCALAR => [qw[SCALAR]],
33 my %sigil = (SCALAR=>'$', ARRAY=>'@', HASH=>'%');
41 my @global_phases = qw(BEGIN CHECK INIT END);
44 croak "Usage: use $_[0] autotie => {AttrName => TieClassName,...}";
47 my $qual_id = qr/^[_a-z]\w*(::[_a-z]\w*)*$/i;
51 return unless $class eq "Attribute::Handlers";
54 if ($cmd =~ /^autotie((?:ref)?)$/) {
55 my $tiedata = ($1 ? '$ref, ' : '') . '@$data';
57 _usage_AH_ $class unless ref($mapping) eq 'HASH';
58 while (my($attr, $tieclass) = each %$mapping) {
59 $tieclass =~ s/^([_a-z]\w*(::[_a-z]\w*)*)(.*)/$1/is;
61 _usage_AH_ $class unless $attr =~ $qual_id
62 && $tieclass =~ $qual_id
63 && eval "use base $tieclass; 1";
64 if ($tieclass->isa('Exporter')) {
65 local $Exporter::ExportLevel = 2;
66 $tieclass->import(eval $args);
68 $attr =~ s/__CALLER__/caller(1)/e;
69 $attr = caller()."::".$attr unless $attr =~ /::/;
71 sub $attr : ATTR(VAR) {
72 my (\$ref, \$data) = \@_[2,4];
73 my \$was_arrayref = ref \$data eq 'ARRAY';
74 \$data = [ \$data ] unless \$was_arrayref;
75 my \$type = ref(\$ref)||"value (".(\$ref||"<undef>").")";
76 (\$type eq 'SCALAR')? tie \$\$ref,'$tieclass',$tiedata
77 :(\$type eq 'ARRAY') ? tie \@\$ref,'$tieclass',$tiedata
78 :(\$type eq 'HASH') ? tie \%\$ref,'$tieclass',$tiedata
79 : die "Can't autotie a \$type\n"
81 } or die "Internal error: $@";
85 croak "Can't understand $_";
89 sub _resolve_lastattr {
90 return unless $lastattr{ref};
91 my $sym = findsym @lastattr{'pkg','ref'}
92 or die "Internal error: $lastattr{pkg} symbol went missing";
93 my $name = *{$sym}{NAME};
94 warn "Declaration of $name attribute in package $lastattr{pkg} may clash with future reserved word\n"
95 if $^W and $name !~ /[A-Z]/;
96 foreach ( @{$validtype{$lastattr{type}}} ) {
97 *{"$lastattr{pkg}::_ATTR_${_}_${name}"} = $lastattr{ref};
103 my ($class) = $AUTOLOAD =~ m/(.*)::/g;
104 $AUTOLOAD =~ m/_ATTR_(.*?)_(.*)/ or
105 croak "Can't locate class method '$AUTOLOAD' via package '$class'";
106 croak "Attribute handler '$3' doesn't handle $2 attributes";
111 my $builtin = qr/lvalue|method|locked/;
113 sub _gen_handler_AH_() {
116 my ($pkg, $ref, @attrs) = @_;
118 my ($attr, $data) = /^([a-z_]\w*)(?:[(](.*)[)])?$/is or next;
119 if ($attr eq 'ATTR') {
121 $raw{$ref} = $data =~ s/\s*,?\s*RAWDATA\s*,?\s*//;
122 $phase{$ref}{BEGIN} = 1
123 if $data =~ s/\s*,?\s*(BEGIN)\s*,?\s*//;
124 $phase{$ref}{INIT} = 1
125 if $data =~ s/\s*,?\s*(INIT)\s*,?\s*//;
126 $phase{$ref}{END} = 1
127 if $data =~ s/\s*,?\s*(END)\s*,?\s*//;
128 $phase{$ref}{CHECK} = 1
129 if $data =~ s/\s*,?\s*(CHECK)\s*,?\s*//
130 || ! keys %{$phase{$ref}};
131 # Added for cleanup to not pollute next call.
133 croak "Can't have two ATTR specifiers on one subroutine"
135 croak "Bad attribute type: ATTR($data)"
136 unless $validtype{$data};
137 %lastattr=(pkg=>$pkg,ref=>$ref,type=>$data);
140 my $handler = $pkg->can($attr);
141 next unless $handler;
142 my $decl = [$pkg, $ref, $attr, $data,
143 $raw{$handler}, $phase{$handler}];
144 foreach my $gphase (@global_phases) {
145 _apply_handler_AH_($decl,$gphase)
146 if $global_phases{$gphase} <= $global_phase;
148 if ($global_phase != 0) {
149 # if _gen_handler_AH_ is being called after
150 # CHECK it's for a lexical, so make sure
151 # it didn't want to run anything later
153 local $Carp::CarpLevel = 2;
154 carp "Won't be able to apply END handler"
155 if $phase{$handler}{END};
158 push @declarations, $decl
163 return grep {defined && !/$builtin/} @attrs;
167 *{"MODIFY_${_}_ATTRIBUTES"} = _gen_handler_AH_ foreach @{$validtype{ANY}};
168 push @UNIVERSAL::ISA, 'Attribute::Handlers'
169 unless grep /^Attribute::Handlers$/, @UNIVERSAL::ISA;
171 sub _apply_handler_AH_ {
172 my ($declaration, $phase) = @_;
173 my ($pkg, $ref, $attr, $data, $raw, $handlerphase) = @$declaration;
174 return unless $handlerphase->{$phase};
175 # print STDERR "Handling $attr on $ref in $phase with [$data]\n";
177 my $handler = "_ATTR_${type}_${attr}";
178 my $sym = findsym($pkg, $ref);
179 $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL';
181 my $evaled = !$raw && eval("package $pkg; no warnings;
182 local \$SIG{__WARN__}=sub{die}; [$data]");
183 $data = ($evaled && $data =~ /^\s*\[/) ? [$evaled]
184 : ($evaled) ? $evaled
187 (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref),
189 (@$data>1? $data : $data->[0]),
200 _apply_handler_AH_($_,'CHECK') foreach @declarations;
205 _apply_handler_AH_($_,'INIT') foreach @declarations
209 END { $global_phase++; _apply_handler_AH_($_,'END') foreach @declarations }
216 Attribute::Handlers - Simpler definition of attribute handlers
220 This document describes version 0.77 of Attribute::Handlers,
221 released June 8, 2002.
227 use Attribute::Handlers;
228 no warnings 'redefine';
231 sub Good : ATTR(SCALAR) {
232 my ($package, $symbol, $referent, $attr, $data) = @_;
234 # Invoked for any scalar variable with a :Good attribute,
235 # provided the variable was declared in MyClass (or
236 # a derived class) or typed to MyClass.
238 # Do whatever to $referent here (executed in CHECK phase).
242 sub Bad : ATTR(SCALAR) {
243 # Invoked for any scalar variable with a :Bad attribute,
244 # provided the variable was declared in MyClass (or
245 # a derived class) or typed to MyClass.
249 sub Good : ATTR(ARRAY) {
250 # Invoked for any array variable with a :Good attribute,
251 # provided the variable was declared in MyClass (or
252 # a derived class) or typed to MyClass.
256 sub Good : ATTR(HASH) {
257 # Invoked for any hash variable with a :Good attribute,
258 # provided the variable was declared in MyClass (or
259 # a derived class) or typed to MyClass.
263 sub Ugly : ATTR(CODE) {
264 # Invoked for any subroutine declared in MyClass (or a
265 # derived class) with an :Ugly attribute.
270 # Invoked for any scalar, array, hash, or subroutine
271 # with an :Omni attribute, provided the variable or
272 # subroutine was declared in MyClass (or a derived class)
273 # or the variable was typed to MyClass.
274 # Use ref($_[2]) to determine what kind of referent it was.
279 use Attribute::Handlers autotie => { Cycle => Tie::Cycle };
281 my $next : Cycle(['A'..'Z']);
286 This module, when inherited by a package, allows that package's class to
287 define attribute handler subroutines for specific attributes. Variables
288 and subroutines subsequently defined in that package, or in packages
289 derived from that package may be given attributes with the same names as
290 the attribute handler subroutines, which will then be called in one of
291 the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END>
294 To create a handler, define it as a subroutine with the same name as
295 the desired attribute, and declare the subroutine itself with the
296 attribute C<:ATTR>. For example:
299 use Attribute::Handlers;
302 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
305 *{$symbol}{NAME}, " ",
306 "($referent) ", "was just declared ",
307 "and ascribed the ${attr} attribute ",
308 "with data ($data)\n",
312 This creates a handler for the attribute C<:Loud> in the class LoudDecl.
313 Thereafter, any subroutine declared with a C<:Loud> attribute in the class
320 causes the above handler to be invoked, and passed:
326 the name of the package into which it was declared;
330 a reference to the symbol table entry (typeglob) containing the subroutine;
334 a reference to the subroutine;
338 the name of the attribute;
342 any data associated with that attribute;
346 the name of the phase in which the handler is being invoked.
350 Likewise, declaring any variables with the C<:Loud> attribute within the
359 will cause the handler to be called with a similar argument list (except,
360 of course, that C<$_[2]> will be a reference to the variable).
362 The package name argument will typically be the name of the class into
363 which the subroutine was declared, but it may also be the name of a derived
364 class (since handlers are inherited).
366 If a lexical variable is given an attribute, there is no symbol table to
367 which it belongs, so the symbol table argument (C<$_[1]>) is set to the
368 string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to
369 an anonymous subroutine results in a symbol table argument of C<'ANON'>.
371 The data argument passes in the value (if any) associated with the
372 attribute. For example, if C<&foo> had been declared:
374 sub foo :Loud("turn it up to 11, man!") {...}
376 then the string C<"turn it up to 11, man!"> would be passed as the
379 Attribute::Handlers makes strenuous efforts to convert
380 the data argument (C<$_[4]>) to a useable form before passing it to
381 the handler (but see L<"Non-interpretive attribute handlers">).
382 For example, all of these:
384 sub foo :Loud(till=>ears=>are=>bleeding) {...}
385 sub foo :Loud(['till','ears','are','bleeding']) {...}
386 sub foo :Loud(qw/till ears are bleeding/) {...}
387 sub foo :Loud(qw/my, ears, are, bleeding/) {...}
388 sub foo :Loud(till,ears,are,bleeding) {...}
390 causes it to pass C<['till','ears','are','bleeding']> as the handler's
391 data argument. However, if the data can't be parsed as valid Perl, then
392 it is passed as an uninterpreted string. For example:
394 sub foo :Loud(my,ears,are,bleeding) {...}
395 sub foo :Loud(qw/my ears are bleeding) {...}
397 cause the strings C<'my,ears,are,bleeding'> and C<'qw/my ears are bleeding'>
398 respectively to be passed as the data argument.
400 If the attribute has only a single associated scalar data value, that value is
401 passed as a scalar. If multiple values are associated, they are passed as an
402 array reference. If no value is associated with the attribute, C<undef> is
406 =head2 Typed lexicals
408 Regardless of the package in which it is declared, if a lexical variable is
409 ascribed an attribute, the handler that is invoked is the one belonging to
410 the package to which it is typed. For example, the following declarations:
414 my LoudDecl $loudobj : Loud;
415 my LoudDecl @loudobjs : Loud;
416 my LoudDecl %loudobjex : Loud;
418 causes the LoudDecl::Loud handler to be invoked (even if OtherClass also
419 defines a handler for C<:Loud> attributes).
422 =head2 Type-specific attribute handlers
424 If an attribute handler is declared and the C<:ATTR> specifier is
425 given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>),
426 the handler is only applied to declarations of that type. For example,
427 the following definition:
431 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
433 creates an attribute handler that applies only to scalars:
439 my $metal : RealLoud; # invokes &LoudDecl::RealLoud
440 my @metal : RealLoud; # error: unknown attribute
441 my %metal : RealLoud; # error: unknown attribute
442 sub metal : RealLoud {...} # error: unknown attribute
444 You can, of course, declare separate handlers for these types as well
445 (but you'll need to specify C<no warnings 'redefine'> to do it quietly):
448 use Attribute::Handlers;
449 no warnings 'redefine';
451 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
452 sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" }
453 sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" }
454 sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" }
456 You can also explicitly indicate that a single handler is meant to be
457 used for all types of referents like so:
460 use Attribute::Handlers;
462 sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" }
464 (I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>).
467 =head2 Non-interpretive attribute handlers
469 Occasionally the strenuous efforts Attribute::Handlers makes to convert
470 the data argument (C<$_[4]>) to a useable form before passing it to
471 the handler get in the way.
473 You can turn off that eagerness-to-help by declaring
474 an attribute handler with the keyword C<RAWDATA>. For example:
476 sub Raw : ATTR(RAWDATA) {...}
477 sub Nekkid : ATTR(SCALAR,RAWDATA) {...}
478 sub Au::Naturale : ATTR(RAWDATA,ANY) {...}
480 Then the handler makes absolutely no attempt to interpret the data it
481 receives and simply passes it as a string:
483 my $power : Raw(1..100); # handlers receives "1..100"
485 =head2 Phase-specific attribute handlers
487 By default, attribute handlers are called at the end of the compilation
488 phase (in a C<CHECK> block). This seems to be optimal in most cases because
489 most things that can be defined are defined by that point but nothing has
492 However, it is possible to set up attribute handlers that are called at
493 other points in the program's compilation or execution, by explicitly
494 stating the phase (or phases) in which you wish the attribute handler to
495 be called. For example:
497 sub Early :ATTR(SCALAR,BEGIN) {...}
498 sub Normal :ATTR(SCALAR,CHECK) {...}
499 sub Late :ATTR(SCALAR,INIT) {...}
500 sub Final :ATTR(SCALAR,END) {...}
501 sub Bookends :ATTR(SCALAR,BEGIN,END) {...}
503 As the last example indicates, a handler may be set up to be (re)called in
504 two or more phases. The phase name is passed as the handler's final argument.
506 Note that attribute handlers that are scheduled for the C<BEGIN> phase
507 are handled as soon as the attribute is detected (i.e. before any
508 subsequently defined C<BEGIN> blocks are executed).
511 =head2 Attributes as C<tie> interfaces
513 Attributes make an excellent and intuitive interface through which to tie
514 variables. For example:
516 use Attribute::Handlers;
519 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
520 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
521 $data = [ $data ] unless ref $data eq 'ARRAY';
522 tie $$referent, 'Tie::Cycle', $data;
529 my $next : Cycle('A'..'Z'); # $next is now a tied variable
535 Note that, because the C<Cycle> attribute receives its arguments in the
536 C<$data> variable, if the attribute is given a list of arguments, C<$data>
537 will consist of a single array reference; otherwise, it will consist of the
538 single argument directly. Since Tie::Cycle requires its cycling values to
539 be passed as an array reference, this means that we need to wrap
540 non-array-reference arguments in an array constructor:
542 $data = [ $data ] unless ref $data eq 'ARRAY';
544 Typically, however, things are the other way around: the tieable class expects
545 its arguments as a flattened list, so the attribute looks like:
547 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
548 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
549 my @data = ref $data eq 'ARRAY' ? @$data : $data;
550 tie $$referent, 'Tie::Whatever', @data;
554 This software pattern is so widely applicable that Attribute::Handlers
555 provides a way to automate it: specifying C<'autotie'> in the
556 C<use Attribute::Handlers> statement. So, the cycling example,
557 could also be written:
559 use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' };
565 my $next : Cycle(['A'..'Z']); # $next is now a tied variable
570 Note that we now have to pass the cycling values as an array reference,
571 since the C<autotie> mechanism passes C<tie> a list of arguments as a list
572 (as in the Tie::Whatever example), I<not> as an array reference (as in
573 the original Tie::Cycle example at the start of this section).
575 The argument after C<'autotie'> is a reference to a hash in which each key is
576 the name of an attribute to be created, and each value is the class to which
577 variables ascribed that attribute should be tied.
579 Note that there is no longer any need to import the Tie::Cycle module --
580 Attribute::Handlers takes care of that automagically. You can even pass
581 arguments to the module's C<import> subroutine, by appending them to the
582 class name. For example:
584 use Attribute::Handlers
585 autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' };
587 If the attribute name is unqualified, the attribute is installed in the
588 current package. Otherwise it is installed in the qualifier's package:
592 use Attribute::Handlers autotie => {
593 Other::Good => Tie::SecureHash, # tie attr installed in Other::
594 Bad => Tie::Taxes, # tie attr installed in Here::
595 UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere
598 Autoties are most commonly used in the module to which they actually tie,
599 and need to export their attributes to any module that calls them. To
600 facilitiate this, Attribute::Handlers recognizes a special "pseudo-class" --
601 C<__CALLER__>, which may be specified as the qualifier of an attribute:
603 package Tie::Me::Kangaroo:Down::Sport;
605 use Attribute::Handlers autotie => { __CALLER__::Roo => __PACKAGE__ };
607 This causes Attribute::Handlers to define the C<Roo> attribute in the package
608 that imports the Tie::Me::Kangaroo:Down::Sport module.
610 =head3 Passing the tied object to C<tie>
612 Occasionally it is important to pass a reference to the object being tied
613 to the TIESCALAR, TIEHASH, etc. that ties it.
615 The C<autotie> mechanism supports this too. The following code:
617 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
618 my $var : Selfish(@args);
620 has the same effect as:
622 tie my $var, 'Tie::Selfish', @args;
624 But when C<"autotieref"> is used instead of C<"autotie">:
626 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
627 my $var : Selfish(@args);
629 the effect is to pass the C<tie> call an extra reference to the variable
632 tie my $var, 'Tie::Selfish', \$var, @args;
638 If the class shown in L<SYNOPSIS> were placed in the MyClass.pm
639 module, then the following code:
644 my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
646 package SomeOtherClass;
651 sub fn :Ugly(sister) :Omni('po',tent()) {...}
652 my @arr :Good :Omni(s/cie/nt/);
653 my %hsh :Good(q/bye) :Omni(q/bus/);
656 would cause the following handlers to be invoked:
658 # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
660 MyClass::Good:ATTR(SCALAR)( 'MyClass', # class
661 'LEXICAL', # no typeglob
665 'CHECK', # compiler phase
668 MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class
669 'LEXICAL', # no typeglob
673 'CHECK', # compiler phase
676 MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class
677 'LEXICAL', # no typeglob
680 '-vorous' # eval'd attr data
681 'CHECK', # compiler phase
685 # sub fn :Ugly(sister) :Omni('po',tent()) {...}
687 MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class
688 \*SomeOtherClass::fn, # typeglob
689 \&SomeOtherClass::fn, # referent
691 'sister' # eval'd attr data
692 'CHECK', # compiler phase
695 MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class
696 \*SomeOtherClass::fn, # typeglob
697 \&SomeOtherClass::fn, # referent
699 ['po','acle'] # eval'd attr data
700 'CHECK', # compiler phase
704 # my @arr :Good :Omni(s/cie/nt/);
706 MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class
707 'LEXICAL', # no typeglob
711 'CHECK', # compiler phase
714 MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class
715 'LEXICAL', # no typeglob
718 "" # eval'd attr data
719 'CHECK', # compiler phase
723 # my %hsh :Good(q/bye) :Omni(q/bus/);
725 MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class
726 'LEXICAL', # no typeglob
729 'q/bye' # raw attr data
730 'CHECK', # compiler phase
733 MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class
734 'LEXICAL', # no typeglob
737 'bus' # eval'd attr data
738 'CHECK', # compiler phase
742 Installing handlers into UNIVERSAL, makes them...err..universal.
745 package Descriptions;
746 use Attribute::Handlers;
749 sub name { return $name{$_[2]}||*{$_[1]}{NAME} }
751 sub UNIVERSAL::Name :ATTR {
752 $name{$_[2]} = $_[4];
755 sub UNIVERSAL::Purpose :ATTR {
756 print STDERR "Purpose of ", &name, " is $_[4]\n";
759 sub UNIVERSAL::Unit :ATTR {
760 print STDERR &name, " measured in $_[4]\n";
767 my $capacity : Name(capacity)
768 : Purpose(to store max storage capacity for files)
774 sub foo : Purpose(to foo all data before barring it) { }
783 =item C<Bad attribute type: ATTR(%s)>
785 An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the
786 type of referent it was defined to handle wasn't one of the five permitted:
787 C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>.
789 =item C<Attribute handler %s doesn't handle %s attributes>
791 A handler for attributes of the specified name I<was> defined, but not
792 for the specified type of declaration. Typically encountered whe trying
793 to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR>
794 attribute handler to some other type of variable.
796 =item C<Declaration of %s attribute in package %s may clash with future reserved word>
798 A handler for an attributes with an all-lowercase name was declared. An
799 attribute with an all-lowercase name might have a meaning to Perl
800 itself some day, even though most don't yet. Use a mixed-case attribute
803 =item C<Can't have two ATTR specifiers on one subroutine>
805 You just can't, okay?
806 Instead, put all the specifications together with commas between them
807 in a single C<ATTR(I<specification>)>.
809 =item C<Can't autotie a %s>
811 You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and
812 C<"HASH">. They're the only things (apart from typeglobs -- which are
813 not declarable) that Perl can tie.
815 =item C<Internal error: %s symbol went missing>
817 Something is rotten in the state of the program. An attributed
818 subroutine ceased to exist between the point it was declared and the point
819 at which its attribute handler(s) would have been called.
821 =item C<Won't be able to apply END handler>
823 You have defined an END handler for an attribute that is being applied
824 to a lexical variable. Since the variable may not be available during END
831 Damian Conway (damian@conway.org)
835 There are undoubtedly serious bugs lurking somewhere in code this funky :-)
836 Bug reports and other feedback are most welcome.
840 Copyright (c) 2001, Damian Conway. All Rights Reserved.
841 This module is free software. It may be used, redistributed
842 and/or modified under the same terms as Perl itself.