1 TODO: perl591delta and further
5 perldelta - what is new for perl 5.10.0
9 This document describes the differences between the 5.8.8 release and
12 Many of the bug fixes in 5.10.0 were already seen in the 5.8.X maintenance
13 releases; they are not duplicated here and are documented in the set of
14 man pages named perl58[1-8]?delta.
16 =head1 Incompatible Changes
18 =head2 Packing and UTF-8 strings
22 The semantics of pack() and unpack() regarding UTF-8-encoded data has been
23 changed. Processing is now by default character per character instead of
24 byte per byte on the underlying encoding. Notably, code that used things
25 like C<pack("a*", $string)> to see through the encoding of string will now
26 simply get back the original $string. Packed strings can also get upgraded
27 during processing when you store upgraded characters. You can get the old
28 behaviour by using C<use bytes>.
30 To be consistent with pack(), the C<C0> in unpack() templates indicates
31 that the data is to be processed in character mode, i.e. character by
32 character; on the contrary, C<U0> in unpack() indicates UTF-8 mode, where
33 the packed string is processed in its UTF-8-encoded Unicode form on a byte
34 by byte basis. This is reversed with regard to perl 5.8.X.
36 Moreover, C<C0> and C<U0> can also be used in pack() templates to specify
37 respectively character and byte modes.
39 C<C0> and C<U0> in the middle of a pack or unpack format now switch to the
40 specified encoding mode, honoring parens grouping. Previously, parens were
43 Also, there is a new pack() character format, C<W>, which is intended to
44 replace the old C<C>. C<C> is kept for unsigned chars coded as bytes in
45 the strings internal representation. C<W> represents unsigned (logical)
46 character values, which can be greater than 255. It is therefore more
47 robust when dealing with potentially UTF-8-encoded data (as C<C> will wrap
48 values outside the range 0..255, and not respect the string encoding).
50 In practice, that means that pack formats are now encoding-neutral, except
53 For consistency, C<A> in unpack() format now trims all Unicode whitespace
54 from the end of the string. Before perl 5.9.2, it used to strip only the
55 classical ASCII space characters.
57 =head2 Byte/character count feature in unpack()
59 A new unpack() template character, C<".">, returns the number of bytes or
60 characters (depending on the selected encoding mode, see above) read so far.
62 =head2 The C<$*> and C<$#> variables have been removed
64 C<$*>, which was deprecated in favor of the C</s> and C</m> regexp
65 modifiers, has been removed.
67 The deprecated C<$#> variable (output format for numbers) has been
70 Two new warnings, C<$#/$* is no longer supported>, have been added.
72 =head2 substr() lvalues are no longer fixed-length
74 The lvalues returned by the three argument form of substr() used to be a
75 "fixed length window" on the original string. In some cases this could
76 cause surprising action at distance or other undefined behaviour. Now the
77 length of the window adjusts itself to the length of the string assigned to
80 =head2 Parsing of C<-f _>
82 The identifier C<_> is now forced to be a bareword after a filetest
83 operator. This solves a number of misparsing issues when a global C<_>
84 subroutine is defined.
88 The C<:unique> attribute has been made a no-op, since its current
89 implementation was fundamentally flawed and not threadsafe.
91 =head2 Scoping of the C<sort> pragma
93 The C<sort> pragma is now lexically scoped. Its effect used to be global.
95 =head2 Scoping of C<bignum>, C<bigint>, C<bigrat>
97 The three numeric pragmas C<bignum>, C<bigint> and C<bigrat> are now
98 lexically scoped. (Tels)
100 =head2 Effect of pragmas in eval
102 The compile-time value of the C<%^H> hint variable can now propagate into
103 eval("")uated code. This makes it more useful to implement lexical
106 As a side-effect of this, the overloaded-ness of constants now propagates
111 A bareword argument to chdir() is now recognized as a file handle.
112 Earlier releases interpreted the bareword as a directory name.
115 =head2 Handling of .pmc files
117 An old feature of perl was that before C<require> or C<use> look for a
118 file with a F<.pm> extension, they will first look for a similar filename
119 with a F<.pmc> extension. If this file is found, it will be loaded in
120 place of any potentially existing file ending in a F<.pm> extension.
122 Previously, F<.pmc> files were loaded only if more recent than the
123 matching F<.pm> file. Starting with 5.9.4, they'll be always loaded if
126 =head2 @- and @+ in patterns
128 The special arrays C<@-> and C<@+> are no longer interpolated in regular
129 expressions. (Sadahiro Tomoyuki)
131 =head2 $AUTOLOAD can now be tainted
133 If you call a subroutine by a tainted name, and if it defers to an
134 AUTOLOAD function, then $AUTOLOAD will be (correctly) tainted.
137 =head2 Tainting and printf
139 When perl is run under taint mode, C<printf()> and C<sprintf()> will now
140 reject any tainted format argument. (Rafael Garcia-Suarez)
142 =head2 undef and signal handlers
144 Undefining or deleting a signal handler via C<undef $SIG{FOO}> is now
145 equivalent to setting it to C<'DEFAULT'>. (Rafael Garcia-Suarez)
147 =head2 strictures and array/hash dereferencing in defined()
149 C<defined @$foo> and C<defined %$bar> are now subject to C<strict 'refs'>
150 (that is, C<$foo> and C<$bar> shall be proper references there.)
153 (However, C<defined(@foo)> and C<defined(%bar)> are discouraged constructs
156 =head2 C<(?p{})> has been removed
158 The regular expression construct C<(?p{})>, which was deprecated in perl
159 5.8, has been removed. Use C<(??{})> instead. (Rafael Garcia-Suarez)
161 =head2 Pseudo-hashes have been removed
163 Support for pseudo-hashes has been removed from Perl 5.9. (The C<fields>
164 pragma remains here, but uses an alternate implementation.)
166 =head2 Removal of the bytecode compiler and of perlcc
168 C<perlcc>, the byteloader and the supporting modules (B::C, B::CC,
169 B::Bytecode, etc.) are no longer distributed with the perl sources. Those
170 experimental tools have never worked reliably, and, due to the lack of
171 volunteers to keep them in line with the perl interpreter developments, it
172 was decided to remove them instead of shipping a broken version of those.
173 The last version of those modules can be found with perl 5.9.4.
175 However the B compiler framework stays supported in the perl core, as with
176 the more useful modules it has permitted (among others, B::Deparse and
179 =head2 Removal of the JPL
181 The JPL (Java-Perl Linguo) has been removed from the perl sources tarball.
183 =head2 Recursive inheritance detected earlier
185 Perl will now immediately throw an exception if you modify any package's
186 C<@ISA> in such a way that it would cause recursive inheritance.
188 Previously, the exception would not occur until Perl attempted to make
189 use of the recursive inheritance while resolving a method or doing a
190 C<$foo-E<gt>isa($bar)> lookup.
192 =head1 Core Enhancements
194 =head2 The C<feature> pragma
196 The C<feature> pragma is used to enable new syntax that would break Perl's
197 backwards-compatibility with older releases of the language. It's a lexical
198 pragma, like C<strict> or C<warnings>.
200 Currently the following new features are available: C<switch> (adds a
201 switch statement), C<say> (adds a C<say> built-in function), and C<state>
202 (adds an C<state> keyword for declaring "static" variables). Those
203 features are described in their own sections of this document.
205 The C<feature> pragma is also implicitly loaded when you require a minimal
206 perl version (with the C<use VERSION> construct) greater than, or equal
207 to, 5.9.5. See L<feature> for details.
209 =head2 New B<-E> command-line switch
211 B<-E> is equivalent to B<-e>, but it implicitly enables all
212 optional features (like C<use feature ":5.10">).
214 =head2 Defined-or operator
216 A new operator C<//> (defined-or) has been implemented.
217 The following statement:
221 is merely equivalent to
229 can now be used instead of
231 $c = $d unless defined $c;
233 The C<//> operator has the same precedence and associativity as C<||>.
234 Special care has been taken to ensure that this operator Do What You Mean
235 while not breaking old code, but some edge cases involving the empty
236 regular expression may now parse differently. See L<perlop> for
239 =head2 Switch and Smart Match operator
241 Perl 5 now has a switch statement. It's available when C<use feature
242 'switch'> is in effect. This feature introduces three new keywords,
243 C<given>, C<when>, and C<default>:
246 when (/^abc/) { $abc = 1; }
247 when (/^def/) { $def = 1; }
248 when (/^xyz/) { $xyz = 1; }
249 default { $nothing = 1; }
252 A more complete description of how Perl matches the switch variable
253 against the C<when> conditions is given in L<perlsyn/"Switch statements">.
255 This kind of match is called I<smart match>, and it's also possible to use
256 it outside of switch statements, via the new C<~~> operator. See
257 L<perlsyn/"Smart matching in detail">.
259 This feature was contributed by Robin Houston.
261 =head2 Regular expressions
265 =item Recursive Patterns
267 It is now possible to write recursive patterns without using the C<(??{})>
268 construct. This new way is more efficient, and in many cases easier to
271 Each capturing parenthesis can now be treated as an independent pattern
272 that can be entered by using the C<(?PARNO)> syntax (C<PARNO> standing for
273 "parenthesis number"). For example, the following pattern will match
274 nested balanced angle brackets:
278 ( # start capture buffer 1
279 < # match an opening angle bracket
281 (?> # don't backtrack over the inside of this group
282 [^<>]+ # one or more non angle brackets
283 ) # end non backtracking group
285 (?1) # recurse to bracket 1 and try it again
286 )* # 0 or more times.
287 > # match a closing angle bracket
288 ) # end capture buffer one
292 Note, users experienced with PCRE will find that the Perl implementation
293 of this feature differs from the PCRE one in that it is possible to
294 backtrack into a recursed pattern, whereas in PCRE the recursion is
295 atomic or "possessive" in nature. (Yves Orton)
297 =item Named Capture Buffers
299 It is now possible to name capturing parenthesis in a pattern and refer to
300 the captured contents by name. The naming syntax is C<< (?<NAME>....) >>.
301 It's possible to backreference to a named buffer with the C<< \k<NAME> >>
302 syntax. In code, the new magical hashes C<%+> and C<%-> can be used to
303 access the contents of the capture buffers.
305 Thus, to replace all doubled chars, one could write
307 s/(?<letter>.)\k<letter>/$+{letter}/g
309 Only buffers with defined contents will be "visible" in the C<%+> hash, so
310 it's possible to do something like
312 foreach my $name (keys %+) {
313 print "content of buffer '$name' is $+{$name}\n";
316 The C<%-> hash is a bit more complete, since it will contain array refs
317 holding values from all capture buffers similarly named, if there should
320 C<%+> and C<%-> are implemented as tied hashes through the new module
321 C<Tie::Hash::NamedCapture>.
323 Users exposed to the .NET regex engine will find that the perl
324 implementation differs in that the numerical ordering of the buffers
325 is sequential, and not "unnamed first, then named". Thus in the pattern
327 /(A)(?<B>B)(C)(?<D>D)/
329 $1 will be 'A', $2 will be 'B', $3 will be 'C' and $4 will be 'D' and not
330 $1 is 'A', $2 is 'C' and $3 is 'B' and $4 is 'D' that a .NET programmer
331 would expect. This is considered a feature. :-) (Yves Orton)
333 =item Possessive Quantifiers
335 Perl now supports the "possessive quantifier" syntax of the "atomic match"
336 pattern. Basically a possessive quantifier matches as much as it can and never
337 gives any back. Thus it can be used to control backtracking. The syntax is
338 similar to non-greedy matching, except instead of using a '?' as the modifier
339 the '+' is used. Thus C<?+>, C<*+>, C<++>, C<{min,max}+> are now legal
340 quantifiers. (Yves Orton)
342 =item Backtracking control verbs
344 The regex engine now supports a number of special-purpose backtrack
345 control verbs: (*THEN), (*PRUNE), (*MARK), (*SKIP), (*COMMIT), (*FAIL)
346 and (*ACCEPT). See L<perlre> for their descriptions. (Yves Orton)
348 =item Relative backreferences
350 A new syntax C<\g{N}> or C<\gN> where "N" is a decimal integer allows a
351 safer form of back-reference notation as well as allowing relative
352 backreferences. This should make it easier to generate and embed patterns
353 that contain backreferences. See L<perlre/"Capture buffers">. (Yves Orton)
357 The functionality of Jeff Pinyan's module Regexp::Keep has been added to
358 the core. You can now use in regular expressions the special escape C<\K>
359 as a way to do something like floating length positive lookbehind. It is
360 also useful in substitutions like:
364 that can now be converted to
368 which is much more efficient. (Yves Orton)
370 =item Vertical and horizontal whitespace, and linebreak
372 Regular expressions now recognize the C<\v> and C<\h> escapes, that match
373 vertical and horizontal whitespace, respectively. C<\V> and C<\H>
374 logically match their complements.
376 C<\R> matches a generic linebreak, that is, vertical whitespace, plus
377 the multi-character sequence C<"\x0D\x0A">.
379 =item Unicode Character Classes
381 Perl's regular expression engine now contains support for matching on the
382 intersection of two Unicode character classes. You can also now refer to
383 user-defined character classes from within other user defined character
390 say() is a new built-in, only available when C<use feature 'say'> is in
391 effect, that is similar to print(), but that implicitly appends a newline
392 to the printed string. See L<perlfunc/say>. (Robin Houston)
396 The default variable C<$_> can now be lexicalized, by declaring it like
397 any other lexical variable, with a simple
401 The operations that default on C<$_> will use the lexically-scoped
402 version of C<$_> when it exists, instead of the global C<$_>.
404 In a C<map> or a C<grep> block, if C<$_> was previously my'ed, then the
405 C<$_> inside the block is lexical as well (and scoped to the block).
407 In a scope where C<$_> has been lexicalized, you can still have access to
408 the global version of C<$_> by using C<$::_>, or, more simply, by
409 overriding the lexical declaration with C<our $_>.
411 =head2 The C<_> prototype
413 A new prototype character has been added. C<_> is equivalent to C<$> (it
414 denotes a scalar), but defaults to C<$_> if the corresponding argument
415 isn't supplied. Due to the optional nature of the argument, you can only
416 use it at the end of a prototype, or before a semicolon.
418 This has a small incompatible consequence: the prototype() function has
419 been adjusted to return C<_> for some built-ins in appropriate cases (for
420 example, C<prototype('CORE::rmdir')>). (Rafael Garcia-Suarez)
422 =head2 UNITCHECK blocks
424 C<UNITCHECK>, a new special code block has been introduced, in addition to
425 C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
427 C<CHECK> and C<INIT> blocks, while useful for some specialized purposes,
428 are always executed at the transition between the compilation and the
429 execution of the main program, and thus are useless whenever code is
430 loaded at runtime. On the other hand, C<UNITCHECK> blocks are executed
431 just after the unit which defined them has been compiled. See L<perlmod>
432 for more information. (Alex Gough)
434 =head2 New Pragma, C<mro>
436 A new pragma, C<mro> (for Method Resolution Order) has been added. It
437 permits to switch, on a per-class basis, the algorithm that perl uses to
438 find inherited methods in case of a mutiple inheritance hierachy. The
439 default MRO hasn't changed (DFS, for Depth First Search). Another MRO is
440 available: the C3 algorithm. See L<mro> for more information.
443 Note that, due to changes in the implentation of class hierarchy search,
444 code that used to undef the C<*ISA> glob will most probably break. Anyway,
445 undef'ing C<*ISA> had the side-effect of removing the magic on the @ISA
446 array and should not have been done in the first place.
448 =head2 readpipe() is now overridable
450 The built-in function readpipe() is now overridable. Overriding it permits
451 also to override its operator counterpart, C<qx//> (a.k.a. C<``>).
452 Moreover, it now defaults to C<$_> if no argument is provided. (Rafael
455 =head2 default argument for readline()
457 readline() now defaults to C<*ARGV> if no argument is provided. (Rafael
460 =head2 state() variables
462 A new class of variables has been introduced. State variables are similar
463 to C<my> variables, but are declared with the C<state> keyword in place of
464 C<my>. They're visible only in their lexical scope, but their value is
465 persistent: unlike C<my> variables, they're not undefined at scope entry,
466 but retain their previous value. (Rafael Garcia-Suarez, Nicholas Clark)
468 To use state variables, one needs to enable them by using
472 or by using the C<-E> command-line switch in one-liners.
473 See L<perlsub/"Persistent variables via state()">.
475 =head2 Stacked filetest operators
477 As a new form of syntactic sugar, it's now possible to stack up filetest
478 operators. You can now write C<-f -w -x $file> in a row to mean
479 C<-x $file && -w _ && -f _>. See L<perlfunc/-X>.
481 =head2 UNIVERSAL::DOES()
483 The C<UNIVERSAL> class has a new method, C<DOES()>. It has been added to
484 solve semantic problems with the C<isa()> method. C<isa()> checks for
485 inheritance, while C<DOES()> has been designed to be overridden when
486 module authors use other types of relations between classes (in addition
487 to inheritance). (chromatic)
489 See L<< UNIVERSAL/"$obj->DOES( ROLE )" >>.
491 =head2 C<CLONE_SKIP()>
493 Perl has now support for the C<CLONE_SKIP> special subroutine. Like
494 C<CLONE>, C<CLONE_SKIP> is called once per package; however, it is called
495 just before cloning starts, and in the context of the parent thread. If it
496 returns a true value, then no objects of that class will be cloned. See
497 L<perlmod> for details. (Contributed by Dave Mitchell.)
501 Formats were improved in several ways. A new field, C<^*>, can be used for
502 variable-width, one-line-at-a-time text. Null characters are now handled
503 correctly in picture lines. Using C<@#> and C<~~> together will now
504 produce a compile-time error, as those format fields are incompatible.
505 L<perlform> has been improved, and miscellaneous bugs fixed.
507 =head2 Byte-order modifiers for pack() and unpack()
509 There are two new byte-order modifiers, C<E<gt>> (big-endian) and C<E<lt>>
510 (little-endian), that can be appended to most pack() and unpack() template
511 characters and groups to force a certain byte-order for that type or group.
512 See L<perlfunc/pack> and L<perlpacktut> for details.
516 You can now use C<no> followed by a version number to specify that you
517 want to use a version of perl older than the specified one.
519 =head2 C<chdir>, C<chmod> and C<chown> on filehandles
521 C<chdir>, C<chmod> and C<chown> can now work on filehandles as well as
522 filenames, if the system supports respectively C<fchdir>, C<fchmod> and
523 C<fchown>, thanks to a patch provided by Gisle Aas.
527 C<$(> and C<$)> now return groups in the order where the OS returns them,
528 thanks to Gisle Aas. This wasn't previously the case.
530 =head2 Recursive sort subs
532 You can now use recursive subroutines with sort(), thanks to Robin Houston.
534 =head2 Exceptions in constant folding
536 The constant folding routine is now wrapped in an exception handler, and
537 if folding throws an exception (such as attempting to evaluate 0/0), perl
538 now retains the current optree, rather than aborting the whole program.
539 (Nicholas Clark, Dave Mitchell)
541 =head2 Source filters in @INC
543 It's possible to enhance the mechanism of subroutine hooks in @INC by
544 adding a source filter on top of the filehandle opened and returned by the
545 hook. This feature was planned a long time ago, but wasn't quite working
546 until now. See L<perlfunc/require> for details. (Nicholas Clark)
548 =head2 New internal variables
552 =item C<${^RE_DEBUG_FLAGS}>
554 This variable controls what debug flags are in effect for the regular
555 expression engine when running under C<use re "debug">. See L<re> for
558 =item C<${^CHILD_ERROR_NATIVE}>
560 This variable gives the native status returned by the last pipe close,
561 backtick command, successful call to wait() or waitpid(), or from the
562 system() operator. See L<perlrun> for details. (Contributed by Gisle Aas.)
568 C<unpack()> now defaults to unpacking the C<$_> variable.
570 C<mkdir()> without arguments now defaults to C<$_>.
572 The internal dump output has been improved, so that non-printable characters
573 such as newline and backspace are output in C<\x> notation, rather than
576 The B<-C> option can no longer be used on the C<#!> line. It wasn't
577 working there anyway.
581 The C<PERLIO_DEBUG> environment variable has no longer any effect for
582 setuid scripts and for scripts run with B<-T>.
584 Moreover, with a thread-enabled perl, using C<PERLIO_DEBUG> could lead to
585 an internal buffer overflow. This has been fixed.
589 The copy of the Unicode Character Database included in Perl 5 has
590 been updated to version 5.0.0.
594 MAD, which stands for I<Misc Attribute Decoration>, is a
595 still-in-development work leading to a Perl 5 to Perl 6 converter. To
596 enable it, it's necessary to pass the argument C<-Dmad> to Configure. The
597 obtained perl isn't binary compatible with a regular perl 5.9.4, and has
598 space and speed penalties; moreover not all regression tests still pass
599 with it. (Larry Wall, Nicholas Clark)
601 =head1 Modules and Pragmata
609 C<encoding::warnings>, by Audrey Tang, is a module to emit warnings
610 whenever an ASCII character string containing high-bit bytes is implicitly
611 converted into UTF-8.
615 C<Module::CoreList>, by Richard Clamp, is a small handy module that tells
616 you what versions of core modules ship with any versions of Perl 5. It
617 comes with a command-line frontend, C<corelist>.
621 =head1 Utility Changes
627 The Perl debugger can now save all debugger commands for sourcing later;
628 notably, it can now emulate stepping backwards, by restarting and
629 rerunning all bar the last command from a saved command history.
631 It can also display the parent inheritance tree of a given class, with the
634 Perl has a new -dt command-line flag, which enables threads support in the
639 The C<corelist> utility is now installed with perl (see L</"New modules">
644 C<h2ph> and C<h2xs> have been made a bit more robust with regard to
649 C<find2perl> now assumes C<-print> as a default action. Previously, it
650 needed to be specified explicitly.
652 Several bugs have been fixed in C<find2perl>, regarding C<-exec> and
653 C<-eval>. Also the options C<-path>, C<-ipath> and C<-iname> have been
658 =head1 New Documentation
660 The long-existing feature of C</(?{...})/> regexps setting C<$_> and pos()
663 =head1 Performance Enhancements
669 Sorting arrays in place (C<@a = sort @a>) is now optimized to avoid
670 making a temporary copy of the array.
672 Likewise, C<reverse sort ...> is now optimized to sort in reverse,
673 avoiding the generation of a temporary intermediate list.
677 Access to elements of lexical arrays via a numeric constant between 0 and
678 255 is now faster. (This used to be only the case for global arrays.)
682 The regexp engine now implements the trie optimization : it's able to
683 factorize common prefixes and suffixes in regular expressions. A new
684 special variable, ${^RE_TRIE_MAXBUF}, has been added to fine-tune this
689 =head1 Installation and Configuration Improvements
691 Run-time customization of @INC can be enabled by passing the
692 C<-Dusesitecustomize> flag to configure. When enabled, this will make perl
693 run F<$sitelibexp/sitecustomize.pl> before anything else. This script can
694 then be set up to add additional entries to @INC.
696 There is alpha support for relocatable @INC entries.
698 =head1 Selected Bug Fixes
700 C<strict> wasn't in effect in regexp-eval blocks (C</(?{...})/>).
702 C<$Foo::_> was wrongly forced as C<$main::_>.
704 =head1 New or Changed Diagnostics
706 A new deprecation warning, I<Deprecated use of my() in false conditional>,
707 has been added, to warn against the use of the dubious and deprecated
712 See L<perldiag>. Use C<state> variables instead.
714 A new warning, C<!=~ should be !~>, is emitted to prevent this misspelling
715 of the non-matching operator.
717 The warning I<Newline in left-justified string> has been removed.
719 The error I<Too late for "-T" option> has been reformulated to be more
722 C<perl -V> has several improvements, making it more useable from shell
723 scripts to get the value of configuration variables. See L<perlrun> for
726 =head1 Changed Internals
728 =head2 Reordering of SVt_* constants
730 The relative ordering of constants that define the various types of C<SV>
731 have changed; in particular, C<SVt_PVGV> has been moved before C<SVt_PVLV>,
732 C<SVt_PVAV>, C<SVt_PVHV> and C<SVt_PVCV>. This is unlikely to make any
733 difference unless you have code that explicitly makes assumptions about that
734 ordering. (The inheritance hierarchy of C<B::*> objects has been changed
737 =head2 Removal of CPP symbols
739 The C preprocessor symbols C<PERL_PM_APIVERSION> and
740 C<PERL_XS_APIVERSION>, which were supposed to give the version number of
741 the oldest perl binary-compatible (resp. source-compatible) with the
742 present one, were not used, and sometimes had misleading values. They have
745 =head2 Less space is used by ops
747 The C<BASEOP> structure now uses less space. The C<op_seq> field has been
748 removed and replaced by the one-bit fields C<op_opt>. C<op_type> is now 9
749 bits long. (Consequently, the C<B::OP> class doesn't provide an C<seq>
754 perl's parser is now generated by bison (it used to be generated by
755 byacc.) As a result, it seems to be a bit more robust.
759 =head1 Known Problems
761 There's still a remaining problem in the implementation of the lexical
762 C<$_>: it doesn't work inside C</(?{...})/> blocks. (See the TODO test in
765 =head1 Platform Specific Problems
767 =head1 Reporting Bugs
771 The F<Changes> file and the perl590delta to perl595delta man pages for
772 exhaustive details on what changed.
774 The F<INSTALL> file for how to build Perl.
776 The F<README> file for general stuff.
778 The F<Artistic> and F<Copying> files for copyright information.