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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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18What can we offer you in return? Fame, fortune, and everlasting glory? Maybe
19not, but if your patch is incorporated, then we'll add your name to the
20F<AUTHORS> file, which ships in the official distribution. How many other
21programming languages offer you 1 line of immortality?
938c8732 22
4e577f8b 23=head1 The roadmap to 5.10
938c8732 24
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25The roadmap to 5.10 envisages feature based releases, as various items in this
26TODO are completed.
27
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28=head2 Needed for a 5.9.4 release
29
30=over
31
32=item *
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33
34Review assertions. Review syntax to combine assertions. Assertions could take
35advantage of the lexical pragmas work. L</What hooks would assertions need?>
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36
37=back
38
39=head2 Needed for a 5.9.5 release
40
41=over
42
43=item *
44Implement L</_ prototype character>
45
46=item *
47Implement L</state variables>
48
49=back
50
51=head2 Needed for a 5.9.6 release
52
53Stabilisation. If all goes well, this will be the equivalent of a 5.10-beta.
e50bb9a1 54
0bdfc961 55=head1 Tasks that only need Perl knowledge
e50bb9a1 56
0bdfc961 57=head2 common test code for timed bail out
e50bb9a1 58
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59Write portable self destruct code for tests to stop them burning CPU in
60infinite loops. This needs to avoid using alarm, as some of the tests are
61testing alarm/sleep or timers.
e50bb9a1 62
0bdfc961 63=head2 POD -> HTML conversion in the core still sucks
e50bb9a1 64
938c8732 65Which is crazy given just how simple POD purports to be, and how simple HTML
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66can be. It's not actually I<as> simple as it sounds, particularly with the
67flexibility POD allows for C<=item>, but it would be good to improve the
68visual appeal of the HTML generated, and to avoid it having any validation
69errors. See also L</make HTML install work>, as the layout of installation tree
70is needed to improve the cross-linking.
938c8732 71
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72The addition of C<Pod::Simple> and its related modules may make this task
73easier to complete.
74
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75=head2 Parallel testing
76
77The core regression test suite is getting ever more comprehensive, which has
78the side effect that it takes longer to run. This isn't so good. Investigate
79whether it would be feasible to give the harness script the B<option> of
80running sets of tests in parallel. This would be useful for tests in
81F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
82
83Questions to answer
84
85=over 4
86
87=item 1
88
89How does screen layout work when you're running more than one test?
90
91=item 2
92
93How does the caller of test specify how many tests to run in parallel?
94
95=item 3
96
97How do setup/teardown tests identify themselves?
98
99=back
100
101Pugs already does parallel testing - can their approach be re-used?
102
0bdfc961 103=head2 Make Schwern poorer
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105We should have for everything. When all the core's modules are tested,
106Schwern has promised to donate to $500 to TPF. We may need volunteers to
107hold him upside down and shake vigorously in order to actually extract the
108cash.
3958b146 109
0bdfc961 110See F<t/lib/1_compile.t> for the 3 remaining modules that need tests.
e50bb9a1 111
0bdfc961 112=head2 Improve the coverage of the core tests
e50bb9a1 113
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114Use Devel::Cover to ascertain the core's test coverage, then add tests that
115are currently missing.
30222c0f 116
0bdfc961 117=head2 test B
e50bb9a1 118
0bdfc961 119A full test suite for the B module would be nice.
e50bb9a1 120
0bdfc961 121=head2 A decent benchmark
e50bb9a1 122
617eabfa 123C<perlbench> seems impervious to any recent changes made to the perl core. It
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124would be useful to have a reasonable general benchmarking suite that roughly
125represented what current perl programs do, and measurably reported whether
126tweaks to the core improve, degrade or don't really affect performance, to
127guide people attempting to optimise the guts of perl. Gisle would welcome
128new tests for perlbench.
6168cf99 129
0bdfc961 130=head2 fix tainting bugs
6168cf99 131
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132Fix the bugs revealed by running the test suite with the C<-t> switch (via
133C<make test.taintwarn>).
e50bb9a1 134
0bdfc961 135=head2 Dual life everything
e50bb9a1 136
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137As part of the "dists" plan, anything that doesn't belong in the smallest perl
138distribution needs to be dual lifed. Anything else can be too. Figure out what
139changes would be needed to package that module and its tests up for CPAN, and
140do so. Test it with older perl releases, and fix the problems you find.
e50bb9a1 141
0bdfc961 142=head2 Improving C<threads::shared>
722d2a37 143
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144Investigate whether C<threads::shared> could share aggregates properly with
145only Perl level changes to shared.pm
722d2a37 146
0bdfc961 147=head2 POSIX memory footprint
e50bb9a1 148
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149Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
150various times worked to cut it down. There is probably still fat to cut out -
151for example POSIX passes Exporter some very memory hungry data structures.
e50bb9a1 152
e50bb9a1 153
e50bb9a1 154
e50bb9a1 155
e50bb9a1 156
adebf063 157
adebf063 158
0bdfc961 159=head1 Tasks that need a little sysadmin-type knowledge
e50bb9a1 160
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161Or if you prefer, tasks that you would learn from, and broaden your skills
162base...
e50bb9a1 163
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164=head2 Relocatable perl
165
166The C level patches needed to create a relocatable perl binary are done, as
167is the work on F<Config.pm>. All that's left to do is the C<Configure> tweaking
168to let people specify how they want to do the install.
169
cd793d32 170=head2 make HTML install work
e50bb9a1 171
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172There is an C<installhtml> target in the Makefile. It's marked as
173"experimental". It would be good to get this tested, make it work reliably, and
174remove the "experimental" tag. This would include
175
176=over 4
177
178=item 1
179
180Checking that cross linking between various parts of the documentation works.
181In particular that links work between the modules (files with POD in F<lib/>)
182and the core documentation (files in F<pod/>)
183
184=item 2
185
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186Work out how to split C<perlfunc> into chunks, preferably one per function
187group, preferably with general case code that could be used elsewhere.
188Challenges here are correctly identifying the groups of functions that go
189together, and making the right named external cross-links point to the right
190page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
191C<endservent>, two or more C<=items> giving the different parameter lists, such
192as
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193
194 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
195
196 =item substr EXPR,OFFSET,LENGTH
197
198 =item substr EXPR,OFFSET
199
200and different parameter lists having different meanings. (eg C<select>)
201
202=back
3a89a73c 203
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204=head2 compressed man pages
205
206Be able to install them. This would probably need a configure test to see how
207the system does compressed man pages (same directory/different directory?
208same filename/different filename), as well as tweaking the F<installman> script
209to compress as necessary.
210
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211=head2 Add a code coverage target to the Makefile
212
213Make it easy for anyone to run Devel::Cover on the core's tests. The steps
214to do this manually are roughly
215
216=over 4
217
218=item *
219
220do a normal C<Configure>, but include Devel::Cover as a module to install
221(see F<INSTALL> for how to do this)
222
223=item *
224
225 make perl
226
227=item *
228
229 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
230
231=item *
232
233Process the resulting Devel::Cover database
234
235=back
236
237This just give you the coverage of the F<.pm>s. To also get the C level
238coverage you need to
239
240=over 4
241
242=item *
243
244Additionally tell C<Configure> to use the appropriate C compiler flags for
245C<gcov>
246
247=item *
248
249 make perl.gcov
250
251(instead of C<make perl>)
252
253=item *
254
255After running the tests run C<gcov> to generate all the F<.gcov> files.
256(Including down in the subdirectories of F<ext/>
257
258=item *
259
260(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
261to get their stats into the cover_db directory.
262
263=item *
264
265Then process the Devel::Cover database
266
267=back
268
269It would be good to add a single switch to C<Configure> to specify that you
270wanted to perform perl level coverage, and another to specify C level
271coverage, and have C<Configure> and the F<Makefile> do all the right things
272automatically.
273
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274=head2 Make Config.pm cope with differences between build and installed perl
275
276Quite often vendors ship a perl binary compiled with their (pay-for)
277compilers. People install a free compiler, such as gcc. To work out how to
278build extensions, Perl interrogates C<%Config>, so in this situation
279C<%Config> describes compilers that aren't there, and extension building
280fails. This forces people into choosing between re-compiling perl themselves
281using the compiler they have, or only using modules that the vendor ships.
282
283It would be good to find a way teach C<Config.pm> about the installation setup,
284possibly involving probing at install time or later, so that the C<%Config> in
285a binary distribution better describes the installed machine, when the
286installed machine differs from the build machine in some significant way.
287
46925299 288=head2 make parallel builds work
0bdfc961 289
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290Currently parallel builds (such as C<make -j3>) don't work reliably. We believe
291that this is due to incomplete dependency specification in the F<Makefile>.
292It would be good if someone were able to track down the causes of these
293problems, so that parallel builds worked properly.
0bdfc961 294
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295=head2 linker specification files
296
297Some platforms mandate that you provide a list of a shared library's external
298symbols to the linker, so the core already has the infrastructure in place to
299do this for generating shared perl libraries. My understanding is that the
300GNU toolchain can accept an optional linker specification file, and restrict
301visibility just to symbols declared in that file. It would be good to extend
302F<makedef.pl> to support this format, and to provide a means within
303C<Configure> to enable it. This would allow Unix users to test that the
304export list is correct, and to build a perl that does not pollute the global
305namespace with private symbols.
306
8523e164 307
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308
309
310=head1 Tasks that need a little C knowledge
311
312These tasks would need a little C knowledge, but don't need any specific
313background or experience with XS, or how the Perl interpreter works
314
315=head2 Make it clear from -v if this is the exact official release
89007cb3 316
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317Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
318usually defines one local patch, of the form "MAINT12345" or "RC1". The output
319of perl -v doesn't report that a perl isn't an official release, and this
89007cb3 320information can get lost in bugs reports. Because of this, the minor version
fa11829f 321isn't bumped up until RC time, to minimise the possibility of versions of perl
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322escaping that believe themselves to be newer than they actually are.
323
324It would be useful to find an elegant way to have the "this is an interim
325maintenance release" or "this is a release candidate" in the terse -v output,
326and have it so that it's easy for the pumpking to remove this just as the
327release tarball is rolled up. This way the version pulled out of rsync would
328always say "I'm a development release" and it would be safe to bump the
329reported minor version as soon as a release ships, which would aid perl
330developers.
331
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332This task is really about thinking of an elegant way to arrange the C source
333such that it's trivial for the Pumpking to flag "this is an official release"
334when making a tarball, yet leave the default source saying "I'm not the
335official release".
336
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337=head2 Ordering of "global" variables.
338
339F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
340per-thread under ithreads, where the variables are actually elements in a
341structure. As C dictates, the variables must be laid out in order of
342declaration. There is a comment
343C</* Important ones in the first cache line (if alignment is done right) */>
344which implies that at some point in the past the ordering was carefully chosen
345(at least in part). However, it's clear that the ordering is less than perfect,
346as currently there are things such as 7 C<bool>s in a row, then something
347typically requiring 4 byte alignment, and then an odd C<bool> later on.
348(C<bool>s are typically defined as C<char>s). So it would be good for someone
349to review the ordering of the variables, to see how much alignment padding can
350be removed.
351
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352It's also worth checking that all variables are actually used. Perl 5.8.0
353shipped with C<PL_nrs> still defined in F<thrdvar.h>, despite it being unused
354since a change over a year earlier. Had this been spotted before release, it
355could have been removed, but now it has to remain in the 5.8.x releases to
356keep the structure the same size, to retain binary compatibility.
357
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358=head2 am I hot or not?
359
360The idea of F<pp_hot.c> is that it contains the I<hot> ops, the ops that are
361most commonly used. The idea is that by grouping them, their object code will
362be adjacent in the executable, so they have a greater chance of already being
363in the CPU cache (or swapped in) due to being near another op already in use.
364
365Except that it's not clear if these really are the most commonly used ops. So
366anyone feeling like exercising their skill with coverage and profiling tools
367might want to determine what ops I<really> are the most commonly used. And in
368turn suggest evictions and promotions to achieve a better F<pp_hot.c>.
369
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370=head2 reduce duplication in sv_setsv_flags
371
372C<Perl_sv_setsv_flags> has a comment
373C</* There's a lot of redundancy below but we're going for speed here */>
374
375Whilst this was true 10 years ago, the growing disparity between RAM and CPU
376speeds mean that the trade offs have changed. In addition, the duplicate code
377adds to the maintenance burden. It would be good to see how much of the
378redundancy can be pruned, particular in the less common paths. (Profiling
379tools at the ready...). For example, why does the test for
380"Can't redefine active sort subroutine" need to occur in two places?
381
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382
383
384
0bdfc961 385=head1 Tasks that need a knowledge of XS
e50bb9a1 386
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387These tasks would need C knowledge, and roughly the level of knowledge of
388the perl API that comes from writing modules that use XS to interface to
389C.
390
391=head2 IPv6
392
393Clean this up. Check everything in core works
394
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395=head2 shrink C<GV>s, C<CV>s
396
397By removing unused elements and careful re-ordering, the structures for C<AV>s
398and C<HV>s have recently been shrunk considerably. It's probable that the same
399approach would find savings in C<GV>s and C<CV>s, if not all the other
400larger-than-C<PVMG> types.
401
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402=head2 merge Perl_sv_2[inpu]v
403
404There's a lot of code shared between C<Perl_sv_2iv_flags>,
405C<Perl_sv_2uv_flags>, C<Perl_sv_2nv>, and C<Perl_sv_2pv_flags>. It would be
406interesting to see if some of it can be merged into common shared static
407functions. In particular, C<Perl_sv_2uv_flags> started out as a cut&paste
408from C<Perl_sv_2iv_flags> around 5.005_50 time, and it may be possible to
409replace both with a single function that returns a value or union which is
410split out by the macros in F<sv.h>
411
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412=head2 UTF8 caching code
413
414The string position/offset cache is not optional. It should be.
415
416=head2 Implicit Latin 1 => Unicode translation
417
418Conversions from byte strings to UTF-8 currently map high bit characters
419to Unicode without translation (or, depending on how you look at it, by
420implicitly assuming that the byte strings are in Latin-1). As perl assumes
421the C locale by default, upgrading a string to UTF-8 may change the
422meaning of its contents regarding character classes, case mapping, etc.
423This should probably emit a warning (at least).
424
425This task is incremental - even a little bit of work on it will help.
e50bb9a1 426
cd793d32 427=head2 autovivification
e50bb9a1 428
cd793d32 429Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
e50bb9a1 430
0bdfc961 431This task is incremental - even a little bit of work on it will help.
e50bb9a1 432
0bdfc961 433=head2 Unicode in Filenames
e50bb9a1 434
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435chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
436opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
437system, truncate, unlink, utime, -X. All these could potentially accept
438Unicode filenames either as input or output (and in the case of system
439and qx Unicode in general, as input or output to/from the shell).
440Whether a filesystem - an operating system pair understands Unicode in
441filenames varies.
e50bb9a1 442
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443Known combinations that have some level of understanding include
444Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
445OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
446create Unicode filenames, what forms of Unicode are accepted and used
447(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
448and so on, varies. Finding the right level of interfacing to Perl
449requires some thought. Remember that an OS does not implicate a
450filesystem.
e50bb9a1 451
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452(The Windows -C command flag "wide API support" has been at least
453temporarily retired in 5.8.1, and the -C has been repurposed, see
454L<perlrun>.)
969e704b 455
0bdfc961 456=head2 Unicode in %ENV
969e704b 457
0bdfc961 458Currently the %ENV entries are always byte strings.
e50bb9a1 459
0bdfc961 460=head2 use less 'memory'
e50bb9a1 461
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462Investigate trade offs to switch out perl's choices on memory usage.
463Particularly perl should be able to give memory back.
e50bb9a1 464
0bdfc961 465This task is incremental - even a little bit of work on it will help.
0abe3f7c 466
0bdfc961 467=head2 Re-implement C<:unique> in a way that is actually thread-safe
0abe3f7c 468
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469The old implementation made bad assumptions on several levels. A good 90%
470solution might be just to make C<:unique> work to share the string buffer
471of SvPVs. That way large constant strings can be shared between ithreads,
472such as the configuration information in F<Config>.
0abe3f7c 473
0bdfc961 474=head2 Make tainting consistent
0abe3f7c 475
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476Tainting would be easier to use if it didn't take documented shortcuts and
477allow taint to "leak" everywhere within an expression.
0abe3f7c 478
0bdfc961 479=head2 readpipe(LIST)
0abe3f7c 480
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481system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
482running a shell. readpipe() (the function behind qx//) could be similarly
483extended.
0abe3f7c 484
e50bb9a1 485
e50bb9a1 486
e50bb9a1 487
f86a8bc5 488
0bdfc961 489=head1 Tasks that need a knowledge of the interpreter
3298bd4d 490
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491These tasks would need C knowledge, and knowledge of how the interpreter works,
492or a willingness to learn.
3298bd4d 493
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494=head2 lexical pragmas
495
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496Document the new support for lexical pragmas in 5.9.3 and how %^H works.
497Maybe C<re>, C<encoding>, maybe other pragmas could be made lexical.
0562c0e3 498
d10fc472 499=head2 Attach/detach debugger from running program
1626a787 500
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501The old perltodo notes "With C<gdb>, you can attach the debugger to a running
502program if you pass the process ID. It would be good to do this with the Perl
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503debugger on a running Perl program, although I'm not sure how it would be
504done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
1626a787 505
0bdfc961 506=head2 Constant folding
80b46460 507
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508The peephole optimiser should trap errors during constant folding, and give
509up on the folding, rather than bailing out at compile time. It is quite
510possible that the unfoldable constant is in unreachable code, eg something
511akin to C<$a = 0/0 if 0;>
512
513=head2 LVALUE functions for lists
514
515The old perltodo notes that lvalue functions don't work for list or hash
516slices. This would be good to fix.
517
518=head2 LVALUE functions in the debugger
519
520The old perltodo notes that lvalue functions don't work in the debugger. This
521would be good to fix.
522
523=head2 _ prototype character
524
525Study the possibility of adding a new prototype character, C<_>, meaning
526"this argument defaults to $_".
527
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528=head2 state variables
529
530C<my $foo if 0;> is deprecated, and should be replaced with
531C<state $x = "initial value\n";> the syntax from Perl 6.
532
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533=head2 @INC source filter to Filter::Simple
534
535The second return value from a sub in @INC can be a source filter. This isn't
536documented. It should be changed to use Filter::Simple, tested and documented.
537
538=head2 regexp optimiser optional
539
540The regexp optimiser is not optional. It should configurable to be, to allow
541its performance to be measured, and its bugs to be easily demonstrated.
542
543=head2 UNITCHECK
544
545Introduce a new special block, UNITCHECK, which is run at the end of a
546compilation unit (module, file, eval(STRING) block). This will correspond to
547the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
548O.pm/B.pm backend framework depends on it.
549
550=head2 optional optimizer
551
552Make the peephole optimizer optional. Currently it performs two tasks as
553it walks the optree - genuine peephole optimisations, and necessary fixups of
554ops. It would be good to find an efficient way to switch out the
555optimisations whilst keeping the fixups.
556
557=head2 You WANT *how* many
558
559Currently contexts are void, scalar and list. split has a special mechanism in
560place to pass in the number of return values wanted. It would be useful to
561have a general mechanism for this, backwards compatible and little speed hit.
562This would allow proposals such as short circuiting sort to be implemented
563as a module on CPAN.
564
565=head2 lexical aliases
566
567Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
568
569=head2 entersub XS vs Perl
570
571At the moment pp_entersub is huge, and has code to deal with entering both
572perl and XS subroutines. Subroutine implementations rarely change between
573perl and XS at run time, so investigate using 2 ops to enter subs (one for
574XS, one for perl) and swap between if a sub is redefined.
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575
576=head2 Self ties
577
578self ties are currently illegal because they caused too many segfaults. Maybe
579the causes of these could be tracked down and self-ties on all types re-
580instated.
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581
582=head2 Optimize away @_
583
584The old perltodo notes "Look at the "reification" code in C<av.c>".
585
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586=head2 What hooks would assertions need?
587
588Assertions are in the core, and work. However, assertions needed to be added
589as a core patch, rather than an XS module in ext, or a CPAN module, because
590the core has no hooks in the necessary places. It would be useful to
591investigate what hooks would need to be added to make it possible to provide
592the full assertion support from a CPAN module, so that we aren't constraining
593the imagination of future CPAN authors.
594
595
596
597
598
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599=head1 Big projects
600
601Tasks that will get your name mentioned in the description of the "Highlights
602of 5.10"
603
604=head2 make ithreads more robust
605
4e577f8b 606Generally make ithreads more robust. See also L</iCOW>
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607
608This task is incremental - even a little bit of work on it will help, and
609will be greatly appreciated.
610
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611One bit would be to write the missing code in sv.c:Perl_dirp_dup.
612
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613=head2 iCOW
614
615Sarathy and Arthur have a proposal for an improved Copy On Write which
616specifically will be able to COW new ithreads. If this can be implemented
617it would be a good thing.
618
619=head2 (?{...}) closures in regexps
620
621Fix (or rewrite) the implementation of the C</(?{...})/> closures.
622
623=head2 A re-entrant regexp engine
624
625This will allow the use of a regex from inside (?{ }), (??{ }) and
626(?(?{ })|) constructs.