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Holding a mutex then croak()ing strikes me as deadlock.
[perl5.git] / pod / perltodo.pod
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1=head1 NAME
2
3perltodo - Perl TO-DO List
4
5=head1 DESCRIPTION
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7This is a list of wishes for Perl. The tasks we think are smaller or easier
8are listed first. Anyone is welcome to work on any of these, but it's a good
9idea to first contact I<perl5-porters@perl.org> to avoid duplication of
10effort. By all means contact a pumpking privately first if you prefer.
e50bb9a1 11
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12Whilst patches to make the list shorter are most welcome, ideas to add to
13the list are also encouraged. Check the perl5-porters archives for past
14ideas, and any discussion about them. One set of archives may be found at:
e50bb9a1 15
0bdfc961 16 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
938c8732 17
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938c8732 19
938c8732 20
e50bb9a1 21
0bdfc961 22=head1 Tasks that only need Perl knowledge
e50bb9a1 23
0bdfc961 24=head2 common test code for timed bail out
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26Write portable self destruct code for tests to stop them burning CPU in
27infinite loops. This needs to avoid using alarm, as some of the tests are
28testing alarm/sleep or timers.
e50bb9a1 29
0bdfc961 30=head2 POD -> HTML conversion in the core still sucks
e50bb9a1 31
938c8732 32Which is crazy given just how simple POD purports to be, and how simple HTML
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33can be. It's not actually I<as> simple as it sounds, particularly with the
34flexibility POD allows for C<=item>, but it would be good to improve the
35visual appeal of the HTML generated, and to avoid it having any validation
36errors. See also L</make HTML install work>, as the layout of installation tree
37is needed to improve the cross-linking.
938c8732 38
0bdfc961 39=head2 Make Schwern poorer
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41We should have for everything. When all the core's modules are tested,
42Schwern has promised to donate to $500 to TPF. We may need volunteers to
43hold him upside down and shake vigorously in order to actually extract the
44cash.
3958b146 45
0bdfc961 46See F<t/lib/1_compile.t> for the 3 remaining modules that need tests.
e50bb9a1 47
0bdfc961 48=head2 Improve the coverage of the core tests
e50bb9a1 49
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50Use Devel::Cover to ascertain the core's test coverage, then add tests that
51are currently missing.
30222c0f 52
0bdfc961 53=head2 test B
e50bb9a1 54
0bdfc961 55A full test suite for the B module would be nice.
e50bb9a1 56
0bdfc961 57=head2 A decent benchmark
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59perlbench seems impervious to any recent changes made to the perl core. It
60would be useful to have a reasonable general benchmarking suite that roughly
61represented what current perl programs do, and measurably reported whether
62tweaks to the core improve, degrade or don't really affect performance, to
63guide people attempting to optimise the guts of perl. Gisle would welcome
64new tests for perlbench.
6168cf99 65
0bdfc961 66=head2 fix tainting bugs
6168cf99 67
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68Fix the bugs revealed by running the test suite with the C<-t> switch (via
69C<make test.taintwarn>).
e50bb9a1 70
0bdfc961 71=head2 Dual life everything
e50bb9a1 72
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73As part of the "dists" plan, anything that doesn't belong in the smallest perl
74distribution needs to be dual lifed. Anything else can be too. Figure out what
75changes would be needed to package that module and its tests up for CPAN, and
76do so. Test it with older perl releases, and fix the problems you find.
e50bb9a1 77
0bdfc961 78=head2 Improving C<threads::shared>
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80Investigate whether C<threads::shared> could share aggregates properly with
81only Perl level changes to shared.pm
722d2a37 82
0bdfc961 83=head2 POSIX memory footprint
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85Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
86various times worked to cut it down. There is probably still fat to cut out -
87for example POSIX passes Exporter some very memory hungry data structures.
e50bb9a1 88
e50bb9a1 89
e50bb9a1 90
e50bb9a1 91
e50bb9a1 92
adebf063 93
adebf063 94
0bdfc961 95=head1 Tasks that need a little sysadmin-type knowledge
e50bb9a1 96
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97Or if you prefer, tasks that you would learn from, and broaden your skills
98base...
e50bb9a1 99
cd793d32 100=head2 make HTML install work
e50bb9a1 101
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102There is an C<installhtml> target in the Makefile. It's marked as
103"experimental". It would be good to get this tested, make it work reliably, and
104remove the "experimental" tag. This would include
105
106=over 4
107
108=item 1
109
110Checking that cross linking between various parts of the documentation works.
111In particular that links work between the modules (files with POD in F<lib/>)
112and the core documentation (files in F<pod/>)
113
114=item 2
115
116Work out how to split perlfunc into chunks, preferably one per function group,
117preferably with general case code that could be used elsewhere. Challenges
118here are correctly identifying the groups of functions that go together, and
119making the right named external cross-links point to the right page. Things to
120be aware of are C<-X>, groups such as C<getpwnam> to C<endservent>, two or
121more C<=items> giving the different parameter lists, such as
122
123 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
124
125 =item substr EXPR,OFFSET,LENGTH
126
127 =item substr EXPR,OFFSET
128
129and different parameter lists having different meanings. (eg C<select>)
130
131=back
3a89a73c 132
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133=head2 compressed man pages
134
135Be able to install them. This would probably need a configure test to see how
136the system does compressed man pages (same directory/different directory?
137same filename/different filename), as well as tweaking the F<installman> script
138to compress as necessary.
139
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140=head2 Add a code coverage target to the Makefile
141
142Make it easy for anyone to run Devel::Cover on the core's tests. The steps
143to do this manually are roughly
144
145=over 4
146
147=item *
148
149do a normal C<Configure>, but include Devel::Cover as a module to install
150(see F<INSTALL> for how to do this)
151
152=item *
153
154 make perl
155
156=item *
157
158 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
159
160=item *
161
162Process the resulting Devel::Cover database
163
164=back
165
166This just give you the coverage of the F<.pm>s. To also get the C level
167coverage you need to
168
169=over 4
170
171=item *
172
173Additionally tell C<Configure> to use the appropriate C compiler flags for
174C<gcov>
175
176=item *
177
178 make perl.gcov
179
180(instead of C<make perl>)
181
182=item *
183
184After running the tests run C<gcov> to generate all the F<.gcov> files.
185(Including down in the subdirectories of F<ext/>
186
187=item *
188
189(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
190to get their stats into the cover_db directory.
191
192=item *
193
194Then process the Devel::Cover database
195
196=back
197
198It would be good to add a single switch to C<Configure> to specify that you
199wanted to perform perl level coverage, and another to specify C level
200coverage, and have C<Configure> and the F<Makefile> do all the right things
201automatically.
202
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203=head2 Make Config.pm cope with differences between build and installed perl
204
205Quite often vendors ship a perl binary compiled with their (pay-for)
206compilers. People install a free compiler, such as gcc. To work out how to
207build extensions, Perl interrogates C<%Config>, so in this situation
208C<%Config> describes compilers that aren't there, and extension building
209fails. This forces people into choosing between re-compiling perl themselves
210using the compiler they have, or only using modules that the vendor ships.
211
212It would be good to find a way teach C<Config.pm> about the installation setup,
213possibly involving probing at install time or later, so that the C<%Config> in
214a binary distribution better describes the installed machine, when the
215installed machine differs from the build machine in some significant way.
216
217=head2 Relocatable perl
218
219The C level patches needed to create a relocatable perl binary are done, as
220is the work on Config.pm. All that's left to do is the C<Configure> tweaking
221to let people specify how they want to do the install.
222
46925299 223=head2 make parallel builds work
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225Currently parallel builds (such as C<make -j3>) don't work reliably. We believe
226that this is due to incomplete dependency specification in the F<Makefile>.
227It would be good if someone were able to track down the causes of these
228problems, so that parallel builds worked properly.
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229
230
231
232=head1 Tasks that need a little C knowledge
233
234These tasks would need a little C knowledge, but don't need any specific
235background or experience with XS, or how the Perl interpreter works
236
237=head2 Make it clear from -v if this is the exact official release
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238
239Currently perl from p4/rsync ships with a patchlevel.h file that usually
240defines one local patch, of the form "MAINT12345" or "RC1". The output of
241perl -v doesn't report that a perl isn't an official release, and this
242information can get lost in bugs reports. Because of this, the minor version
fa11829f 243isn't bumped up until RC time, to minimise the possibility of versions of perl
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244escaping that believe themselves to be newer than they actually are.
245
246It would be useful to find an elegant way to have the "this is an interim
247maintenance release" or "this is a release candidate" in the terse -v output,
248and have it so that it's easy for the pumpking to remove this just as the
249release tarball is rolled up. This way the version pulled out of rsync would
250always say "I'm a development release" and it would be safe to bump the
251reported minor version as soon as a release ships, which would aid perl
252developers.
253
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254This task is really about thinking of an elegant way to arrange the C source
255such that it's trivial for the Pumpking to flag "this is an official release"
256when making a tarball, yet leave the default source saying "I'm not the
257official release".
258
259=head2 bincompat functions
260
261There are lots of functions which are retained for binary compatibility.
262Clean these up. Move them to mathom.c, and don't compile for blead?
263
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264=head2 am I hot or not?
265
266The idea of F<pp_hot.c> is that it contains the I<hot> ops, the ops that are
267most commonly used. The idea is that by grouping them, their object code will
268be adjacent in the executable, so they have a greater chance of already being
269in the CPU cache (or swapped in) due to being near another op already in use.
270
271Except that it's not clear if these really are the most commonly used ops. So
272anyone feeling like exercising their skill with coverage and profiling tools
273might want to determine what ops I<really> are the most commonly used. And in
274turn suggest evictions and promotions to achieve a better F<pp_hot.c>.
275
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276=head2 emulate the per-thread memory pool on Unix
277
278For Windows, ithreads allocates memory for each thread from a separate pool,
279which it discards at thread exit. It also checks that memory is free()d to
280the correct pool. Neither check is done on Unix, so code developed there won't
281be subject to such strictures, so can harbour bugs that only show up when the
282code reaches Windows.
283
284It would be good to be able to optionally emulate the Window pool system on
285Unix, to let developers who only have access to Unix, or want to use
286Unix-specific debugging tools, check for these problems. To do this would
287involve figuring out how the C<PerlMem_*> macros wrap C<malloc()> access, and
288providing a layer that records/checks the identity of the thread making the
289call, and recording all the memory allocated by each thread via this API so
290that it can be summarily free()d at thread exit. One implementation idea
291would be to increase the size of allocation, and store the C<my_perl> pointer
292(to identify the thread) at the start, along with pointers to make a linked
293list of blocks for this thread. To avoid alignment problems it would be
294necessary to do something like
295
296 union memory_header_padded {
297 struct memory_header {
298 void *thread_id; /* For my_perl */
299 void *next; /* Pointer to next block for this thread */
300 } data;
301 long double padding; /* whatever type has maximal alignment constraint */
302 };
303
304
305although C<long double> might not be the only type to add to the padding
306union.
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308
309
310
0bdfc961 311=head1 Tasks that need a knowledge of XS
e50bb9a1 312
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313These tasks would need C knowledge, and roughly the level of knowledge of
314the perl API that comes from writing modules that use XS to interface to
315C.
316
317=head2 IPv6
318
319Clean this up. Check everything in core works
320
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321=head2 merge Perl_sv_2[inpu]v
322
323There's a lot of code shared between C<Perl_sv_2iv_flags>,
324C<Perl_sv_2uv_flags>, C<Perl_sv_2nv>, and C<Perl_sv_2pv_flags>. It would be
325interesting to see if some of it can be merged into common shared static
326functions. In particular, C<Perl_sv_2uv_flags> started out as a cut&paste
327from C<Perl_sv_2iv_flags> around 5.005_50 time, and it may be possible to
328replace both with a single function that returns a value or union which is
329split out by the macros in F<sv.h>
330
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331=head2 UTF8 caching code
332
333The string position/offset cache is not optional. It should be.
334
335=head2 Implicit Latin 1 => Unicode translation
336
337Conversions from byte strings to UTF-8 currently map high bit characters
338to Unicode without translation (or, depending on how you look at it, by
339implicitly assuming that the byte strings are in Latin-1). As perl assumes
340the C locale by default, upgrading a string to UTF-8 may change the
341meaning of its contents regarding character classes, case mapping, etc.
342This should probably emit a warning (at least).
343
344This task is incremental - even a little bit of work on it will help.
e50bb9a1 345
cd793d32 346=head2 autovivification
e50bb9a1 347
cd793d32 348Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
e50bb9a1 349
0bdfc961 350This task is incremental - even a little bit of work on it will help.
e50bb9a1 351
0bdfc961 352=head2 Unicode in Filenames
e50bb9a1 353
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354chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
355opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
356system, truncate, unlink, utime, -X. All these could potentially accept
357Unicode filenames either as input or output (and in the case of system
358and qx Unicode in general, as input or output to/from the shell).
359Whether a filesystem - an operating system pair understands Unicode in
360filenames varies.
e50bb9a1 361
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362Known combinations that have some level of understanding include
363Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
364OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
365create Unicode filenames, what forms of Unicode are accepted and used
366(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
367and so on, varies. Finding the right level of interfacing to Perl
368requires some thought. Remember that an OS does not implicate a
369filesystem.
e50bb9a1 370
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371(The Windows -C command flag "wide API support" has been at least
372temporarily retired in 5.8.1, and the -C has been repurposed, see
373L<perlrun>.)
969e704b 374
0bdfc961 375=head2 Unicode in %ENV
969e704b 376
0bdfc961 377Currently the %ENV entries are always byte strings.
e50bb9a1 378
0bdfc961 379=head2 use less 'memory'
e50bb9a1 380
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381Investigate trade offs to switch out perl's choices on memory usage.
382Particularly perl should be able to give memory back.
e50bb9a1 383
0bdfc961 384This task is incremental - even a little bit of work on it will help.
0abe3f7c 385
0bdfc961 386=head2 Re-implement C<:unique> in a way that is actually thread-safe
0abe3f7c 387
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388The old implementation made bad assumptions on several levels. A good 90%
389solution might be just to make C<:unique> work to share the string buffer
390of SvPVs. That way large constant strings can be shared between ithreads,
391such as the configuration information in F<Config>.
0abe3f7c 392
0bdfc961 393=head2 Make tainting consistent
0abe3f7c 394
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395Tainting would be easier to use if it didn't take documented shortcuts and
396allow taint to "leak" everywhere within an expression.
0abe3f7c 397
0bdfc961 398=head2 readpipe(LIST)
0abe3f7c 399
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400system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
401running a shell. readpipe() (the function behind qx//) could be similarly
402extended.
0abe3f7c 403
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e50bb9a1 405
e50bb9a1 406
f86a8bc5 407
0bdfc961 408=head1 Tasks that need a knowledge of the interpreter
3298bd4d 409
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410These tasks would need C knowledge, and knowledge of how the interpreter works,
411or a willingness to learn.
3298bd4d 412
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413=head2 lexical pragmas
414
415Reimplement the mechanism of lexical pragmas to be more extensible. Fix
416current pragmas that don't work well (or at all) with lexical scopes or in
417run-time eval(STRING) (C<sort>, C<re>, C<encoding> for example). MJD has a
418preliminary patch that implements this.
0562c0e3 419
d10fc472 420=head2 Attach/detach debugger from running program
1626a787 421
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422The old perltodo notes "With C<gdb>, you can attach the debugger to a running
423program if you pass the process ID. It would be good to do this with the Perl
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424debugger on a running Perl program, although I'm not sure how it would be
425done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
1626a787 426
0bdfc961 427=head2 inlining autoloaded constants
d10fc472 428
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429Currently the optimiser can inline constants when expressed as subroutines
430with prototype ($) that return a constant. Likewise, many packages wrapping
431C libraries export lots of constants as subroutines which are AUTOLOADed on
432demand. However, these have no prototypes, so can't be seen as constants by
433the optimiser. Some way of cheaply (low syntax, low memory overhead) to the
434perl compiler that a name is a constant would be great, so that it knows to
435call the AUTOLOAD routine at compile time, and then inline the constant.
80b46460 436
0bdfc961 437=head2 Constant folding
80b46460 438
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439The peephole optimiser should trap errors during constant folding, and give
440up on the folding, rather than bailing out at compile time. It is quite
441possible that the unfoldable constant is in unreachable code, eg something
442akin to C<$a = 0/0 if 0;>
443
444=head2 LVALUE functions for lists
445
446The old perltodo notes that lvalue functions don't work for list or hash
447slices. This would be good to fix.
448
449=head2 LVALUE functions in the debugger
450
451The old perltodo notes that lvalue functions don't work in the debugger. This
452would be good to fix.
453
454=head2 _ prototype character
455
456Study the possibility of adding a new prototype character, C<_>, meaning
457"this argument defaults to $_".
458
459=head2 @INC source filter to Filter::Simple
460
461The second return value from a sub in @INC can be a source filter. This isn't
462documented. It should be changed to use Filter::Simple, tested and documented.
463
464=head2 regexp optimiser optional
465
466The regexp optimiser is not optional. It should configurable to be, to allow
467its performance to be measured, and its bugs to be easily demonstrated.
468
469=head2 UNITCHECK
470
471Introduce a new special block, UNITCHECK, which is run at the end of a
472compilation unit (module, file, eval(STRING) block). This will correspond to
473the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
474O.pm/B.pm backend framework depends on it.
475
476=head2 optional optimizer
477
478Make the peephole optimizer optional. Currently it performs two tasks as
479it walks the optree - genuine peephole optimisations, and necessary fixups of
480ops. It would be good to find an efficient way to switch out the
481optimisations whilst keeping the fixups.
482
483=head2 You WANT *how* many
484
485Currently contexts are void, scalar and list. split has a special mechanism in
486place to pass in the number of return values wanted. It would be useful to
487have a general mechanism for this, backwards compatible and little speed hit.
488This would allow proposals such as short circuiting sort to be implemented
489as a module on CPAN.
490
491=head2 lexical aliases
492
493Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
494
495=head2 entersub XS vs Perl
496
497At the moment pp_entersub is huge, and has code to deal with entering both
498perl and XS subroutines. Subroutine implementations rarely change between
499perl and XS at run time, so investigate using 2 ops to enter subs (one for
500XS, one for perl) and swap between if a sub is redefined.
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501
502=head2 Self ties
503
504self ties are currently illegal because they caused too many segfaults. Maybe
505the causes of these could be tracked down and self-ties on all types re-
506instated.
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507
508=head2 Optimize away @_
509
510The old perltodo notes "Look at the "reification" code in C<av.c>".
511
512=head2 switch ops
513
514The old perltodo notes "Although we have C<Switch.pm> in core, Larry points to
515the dormant C<nswitch> and C<cswitch> ops in F<pp.c>; using these opcodes would
516be much faster."
517
518=head2 What hooks would assertions need?
519
520Assertions are in the core, and work. However, assertions needed to be added
521as a core patch, rather than an XS module in ext, or a CPAN module, because
522the core has no hooks in the necessary places. It would be useful to
523investigate what hooks would need to be added to make it possible to provide
524the full assertion support from a CPAN module, so that we aren't constraining
525the imagination of future CPAN authors.
526
527
528
529
530
531
532
533=head1 Big projects
534
535Tasks that will get your name mentioned in the description of the "Highlights
536of 5.10"
537
538=head2 make ithreads more robust
539
540Generally make ithreads more robust. See also L<iCOW>
541
542This task is incremental - even a little bit of work on it will help, and
543will be greatly appreciated.
544
545=head2 iCOW
546
547Sarathy and Arthur have a proposal for an improved Copy On Write which
548specifically will be able to COW new ithreads. If this can be implemented
549it would be a good thing.
550
551=head2 (?{...}) closures in regexps
552
553Fix (or rewrite) the implementation of the C</(?{...})/> closures.
554
555=head2 A re-entrant regexp engine
556
557This will allow the use of a regex from inside (?{ }), (??{ }) and
558(?(?{ })|) constructs.