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Fix tokenizer debugging trace for file tests
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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
938c8732 23
e50bb9a1 24
0bdfc961 25=head1 Tasks that only need Perl knowledge
e50bb9a1 26
0bdfc961 27=head2 common test code for timed bail out
e50bb9a1 28
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29Write portable self destruct code for tests to stop them burning CPU in
30infinite loops. This needs to avoid using alarm, as some of the tests are
31testing alarm/sleep or timers.
e50bb9a1 32
0bdfc961 33=head2 POD -> HTML conversion in the core still sucks
e50bb9a1 34
938c8732 35Which is crazy given just how simple POD purports to be, and how simple HTML
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36can be. It's not actually I<as> simple as it sounds, particularly with the
37flexibility POD allows for C<=item>, but it would be good to improve the
38visual appeal of the HTML generated, and to avoid it having any validation
39errors. See also L</make HTML install work>, as the layout of installation tree
40is needed to improve the cross-linking.
938c8732 41
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42=head2 Parallel testing
43
44The core regression test suite is getting ever more comprehensive, which has
45the side effect that it takes longer to run. This isn't so good. Investigate
46whether it would be feasible to give the harness script the B<option> of
47running sets of tests in parallel. This would be useful for tests in
48F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
49
50Questions to answer
51
52=over 4
53
54=item 1
55
56How does screen layout work when you're running more than one test?
57
58=item 2
59
60How does the caller of test specify how many tests to run in parallel?
61
62=item 3
63
64How do setup/teardown tests identify themselves?
65
66=back
67
68Pugs already does parallel testing - can their approach be re-used?
69
0bdfc961 70=head2 Make Schwern poorer
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72We should have for everything. When all the core's modules are tested,
73Schwern has promised to donate to $500 to TPF. We may need volunteers to
74hold him upside down and shake vigorously in order to actually extract the
75cash.
3958b146 76
0bdfc961 77See F<t/lib/1_compile.t> for the 3 remaining modules that need tests.
e50bb9a1 78
0bdfc961 79=head2 Improve the coverage of the core tests
e50bb9a1 80
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81Use Devel::Cover to ascertain the core's test coverage, then add tests that
82are currently missing.
30222c0f 83
0bdfc961 84=head2 test B
e50bb9a1 85
0bdfc961 86A full test suite for the B module would be nice.
e50bb9a1 87
0bdfc961 88=head2 A decent benchmark
e50bb9a1 89
617eabfa 90C<perlbench> seems impervious to any recent changes made to the perl core. It
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91would be useful to have a reasonable general benchmarking suite that roughly
92represented what current perl programs do, and measurably reported whether
93tweaks to the core improve, degrade or don't really affect performance, to
94guide people attempting to optimise the guts of perl. Gisle would welcome
95new tests for perlbench.
6168cf99 96
0bdfc961 97=head2 fix tainting bugs
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99Fix the bugs revealed by running the test suite with the C<-t> switch (via
100C<make test.taintwarn>).
e50bb9a1 101
0bdfc961 102=head2 Dual life everything
e50bb9a1 103
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104As part of the "dists" plan, anything that doesn't belong in the smallest perl
105distribution needs to be dual lifed. Anything else can be too. Figure out what
106changes would be needed to package that module and its tests up for CPAN, and
107do so. Test it with older perl releases, and fix the problems you find.
e50bb9a1 108
0bdfc961 109=head2 Improving C<threads::shared>
722d2a37 110
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111Investigate whether C<threads::shared> could share aggregates properly with
112only Perl level changes to shared.pm
722d2a37 113
0bdfc961 114=head2 POSIX memory footprint
e50bb9a1 115
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116Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
117various times worked to cut it down. There is probably still fat to cut out -
118for example POSIX passes Exporter some very memory hungry data structures.
e50bb9a1 119
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120=head2 Refactor C<xsubpp> to be a thin wrapper around C<ExtUtils::ParseXS>
121
122C<ExtUtils::ParseXS> encapsulates a version of the C<xsubpp> into a module.
123In effect this is a code fork, and it's likely that C<xsubpp> has had some
124bug fixes since the code from C<ExtUtils::ParseXS> was derived. It would be
125good to merge the differences in, reduce down to 1 canonical implementation,
126and convert C<xsubpp> to a very thin command line wrapper to
127C<ExtUtils::ParseXS>.
128
129In theory this needs no real C knowledge, as one way of approaching this task
130is to ensure that C<ExtUtils::ParseXS> generates identical output to C<xsubpp>
131for input XS files, which does not require understanding the contents of the
132output C file. However, some C knowledge is likely to help with testing, and
133locating/producing comprehensive test cases.
e50bb9a1 134
e50bb9a1 135
e50bb9a1 136
e50bb9a1 137
adebf063 138
adebf063 139
0bdfc961 140=head1 Tasks that need a little sysadmin-type knowledge
e50bb9a1 141
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142Or if you prefer, tasks that you would learn from, and broaden your skills
143base...
e50bb9a1 144
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145=head2 Relocatable perl
146
147The C level patches needed to create a relocatable perl binary are done, as
148is the work on F<Config.pm>. All that's left to do is the C<Configure> tweaking
149to let people specify how they want to do the install.
150
cd793d32 151=head2 make HTML install work
e50bb9a1 152
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153There is an C<installhtml> target in the Makefile. It's marked as
154"experimental". It would be good to get this tested, make it work reliably, and
155remove the "experimental" tag. This would include
156
157=over 4
158
159=item 1
160
161Checking that cross linking between various parts of the documentation works.
162In particular that links work between the modules (files with POD in F<lib/>)
163and the core documentation (files in F<pod/>)
164
165=item 2
166
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167Work out how to split C<perlfunc> into chunks, preferably one per function
168group, preferably with general case code that could be used elsewhere.
169Challenges here are correctly identifying the groups of functions that go
170together, and making the right named external cross-links point to the right
171page. Things to be aware of are C<-X>, groups such as C<getpwnam> to
172C<endservent>, two or more C<=items> giving the different parameter lists, such
173as
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174
175 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
176
177 =item substr EXPR,OFFSET,LENGTH
178
179 =item substr EXPR,OFFSET
180
181and different parameter lists having different meanings. (eg C<select>)
182
183=back
3a89a73c 184
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185=head2 compressed man pages
186
187Be able to install them. This would probably need a configure test to see how
188the system does compressed man pages (same directory/different directory?
189same filename/different filename), as well as tweaking the F<installman> script
190to compress as necessary.
191
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192=head2 Add a code coverage target to the Makefile
193
194Make it easy for anyone to run Devel::Cover on the core's tests. The steps
195to do this manually are roughly
196
197=over 4
198
199=item *
200
201do a normal C<Configure>, but include Devel::Cover as a module to install
202(see F<INSTALL> for how to do this)
203
204=item *
205
206 make perl
207
208=item *
209
210 cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
211
212=item *
213
214Process the resulting Devel::Cover database
215
216=back
217
218This just give you the coverage of the F<.pm>s. To also get the C level
219coverage you need to
220
221=over 4
222
223=item *
224
225Additionally tell C<Configure> to use the appropriate C compiler flags for
226C<gcov>
227
228=item *
229
230 make perl.gcov
231
232(instead of C<make perl>)
233
234=item *
235
236After running the tests run C<gcov> to generate all the F<.gcov> files.
237(Including down in the subdirectories of F<ext/>
238
239=item *
240
241(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
242to get their stats into the cover_db directory.
243
244=item *
245
246Then process the Devel::Cover database
247
248=back
249
250It would be good to add a single switch to C<Configure> to specify that you
251wanted to perform perl level coverage, and another to specify C level
252coverage, and have C<Configure> and the F<Makefile> do all the right things
253automatically.
254
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255=head2 Make Config.pm cope with differences between build and installed perl
256
257Quite often vendors ship a perl binary compiled with their (pay-for)
258compilers. People install a free compiler, such as gcc. To work out how to
259build extensions, Perl interrogates C<%Config>, so in this situation
260C<%Config> describes compilers that aren't there, and extension building
261fails. This forces people into choosing between re-compiling perl themselves
262using the compiler they have, or only using modules that the vendor ships.
263
264It would be good to find a way teach C<Config.pm> about the installation setup,
265possibly involving probing at install time or later, so that the C<%Config> in
266a binary distribution better describes the installed machine, when the
267installed machine differs from the build machine in some significant way.
268
46925299 269=head2 make parallel builds work
0bdfc961 270
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271Currently parallel builds (such as C<make -j3>) don't work reliably. We believe
272that this is due to incomplete dependency specification in the F<Makefile>.
273It would be good if someone were able to track down the causes of these
274problems, so that parallel builds worked properly.
0bdfc961 275
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276=head2 linker specification files
277
278Some platforms mandate that you provide a list of a shared library's external
279symbols to the linker, so the core already has the infrastructure in place to
280do this for generating shared perl libraries. My understanding is that the
281GNU toolchain can accept an optional linker specification file, and restrict
282visibility just to symbols declared in that file. It would be good to extend
283F<makedef.pl> to support this format, and to provide a means within
284C<Configure> to enable it. This would allow Unix users to test that the
285export list is correct, and to build a perl that does not pollute the global
286namespace with private symbols.
287
8523e164 288
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289
290
291=head1 Tasks that need a little C knowledge
292
293These tasks would need a little C knowledge, but don't need any specific
294background or experience with XS, or how the Perl interpreter works
295
296=head2 Make it clear from -v if this is the exact official release
89007cb3 297
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298Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
299usually defines one local patch, of the form "MAINT12345" or "RC1". The output
300of perl -v doesn't report that a perl isn't an official release, and this
89007cb3 301information can get lost in bugs reports. Because of this, the minor version
fa11829f 302isn't bumped up until RC time, to minimise the possibility of versions of perl
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303escaping that believe themselves to be newer than they actually are.
304
305It would be useful to find an elegant way to have the "this is an interim
306maintenance release" or "this is a release candidate" in the terse -v output,
307and have it so that it's easy for the pumpking to remove this just as the
308release tarball is rolled up. This way the version pulled out of rsync would
309always say "I'm a development release" and it would be safe to bump the
310reported minor version as soon as a release ships, which would aid perl
311developers.
312
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313This task is really about thinking of an elegant way to arrange the C source
314such that it's trivial for the Pumpking to flag "this is an official release"
315when making a tarball, yet leave the default source saying "I'm not the
316official release".
317
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318=head2 Tidy up global variables
319
320There's a note in F<intrpvar.h>
321
322 /* These two variables are needed to preserve 5.8.x bincompat because
323 we can't change function prototypes of two exported functions.
324 Probably should be taken out of blead soon, and relevant prototypes
325 changed. */
326
327So doing this, and removing any of the unused variables still present would
328be good.
329
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330=head2 Ordering of "global" variables.
331
332F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
333per-thread under ithreads, where the variables are actually elements in a
334structure. As C dictates, the variables must be laid out in order of
335declaration. There is a comment
336C</* Important ones in the first cache line (if alignment is done right) */>
337which implies that at some point in the past the ordering was carefully chosen
338(at least in part). However, it's clear that the ordering is less than perfect,
339as currently there are things such as 7 C<bool>s in a row, then something
340typically requiring 4 byte alignment, and then an odd C<bool> later on.
341(C<bool>s are typically defined as C<char>s). So it would be good for someone
342to review the ordering of the variables, to see how much alignment padding can
343be removed.
344
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345=head2 bincompat functions
346
347There are lots of functions which are retained for binary compatibility.
348Clean these up. Move them to mathom.c, and don't compile for blead?
349
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350=head2 am I hot or not?
351
352The idea of F<pp_hot.c> is that it contains the I<hot> ops, the ops that are
353most commonly used. The idea is that by grouping them, their object code will
354be adjacent in the executable, so they have a greater chance of already being
355in the CPU cache (or swapped in) due to being near another op already in use.
356
357Except that it's not clear if these really are the most commonly used ops. So
358anyone feeling like exercising their skill with coverage and profiling tools
359might want to determine what ops I<really> are the most commonly used. And in
360turn suggest evictions and promotions to achieve a better F<pp_hot.c>.
361
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362=head2 emulate the per-thread memory pool on Unix
363
364For Windows, ithreads allocates memory for each thread from a separate pool,
365which it discards at thread exit. It also checks that memory is free()d to
366the correct pool. Neither check is done on Unix, so code developed there won't
367be subject to such strictures, so can harbour bugs that only show up when the
368code reaches Windows.
369
370It would be good to be able to optionally emulate the Window pool system on
371Unix, to let developers who only have access to Unix, or want to use
372Unix-specific debugging tools, check for these problems. To do this would
373involve figuring out how the C<PerlMem_*> macros wrap C<malloc()> access, and
374providing a layer that records/checks the identity of the thread making the
375call, and recording all the memory allocated by each thread via this API so
376that it can be summarily free()d at thread exit. One implementation idea
377would be to increase the size of allocation, and store the C<my_perl> pointer
378(to identify the thread) at the start, along with pointers to make a linked
379list of blocks for this thread. To avoid alignment problems it would be
380necessary to do something like
381
382 union memory_header_padded {
383 struct memory_header {
384 void *thread_id; /* For my_perl */
385 void *next; /* Pointer to next block for this thread */
386 } data;
387 long double padding; /* whatever type has maximal alignment constraint */
388 };
389
390
391although C<long double> might not be the only type to add to the padding
392union.
62403a3c 393
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394=head2 reduce duplication in sv_setsv_flags
395
396C<Perl_sv_setsv_flags> has a comment
397C</* There's a lot of redundancy below but we're going for speed here */>
398
399Whilst this was true 10 years ago, the growing disparity between RAM and CPU
400speeds mean that the trade offs have changed. In addition, the duplicate code
401adds to the maintenance burden. It would be good to see how much of the
402redundancy can be pruned, particular in the less common paths. (Profiling
403tools at the ready...). For example, why does the test for
404"Can't redefine active sort subroutine" need to occur in two places?
405
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406
407
408
0bdfc961 409=head1 Tasks that need a knowledge of XS
e50bb9a1 410
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411These tasks would need C knowledge, and roughly the level of knowledge of
412the perl API that comes from writing modules that use XS to interface to
413C.
414
415=head2 IPv6
416
417Clean this up. Check everything in core works
418
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419=head2 shrink C<GV>s, C<CV>s
420
421By removing unused elements and careful re-ordering, the structures for C<AV>s
422and C<HV>s have recently been shrunk considerably. It's probable that the same
423approach would find savings in C<GV>s and C<CV>s, if not all the other
424larger-than-C<PVMG> types.
425
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426=head2 merge Perl_sv_2[inpu]v
427
428There's a lot of code shared between C<Perl_sv_2iv_flags>,
429C<Perl_sv_2uv_flags>, C<Perl_sv_2nv>, and C<Perl_sv_2pv_flags>. It would be
430interesting to see if some of it can be merged into common shared static
431functions. In particular, C<Perl_sv_2uv_flags> started out as a cut&paste
432from C<Perl_sv_2iv_flags> around 5.005_50 time, and it may be possible to
433replace both with a single function that returns a value or union which is
434split out by the macros in F<sv.h>
435
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436=head2 UTF8 caching code
437
438The string position/offset cache is not optional. It should be.
439
440=head2 Implicit Latin 1 => Unicode translation
441
442Conversions from byte strings to UTF-8 currently map high bit characters
443to Unicode without translation (or, depending on how you look at it, by
444implicitly assuming that the byte strings are in Latin-1). As perl assumes
445the C locale by default, upgrading a string to UTF-8 may change the
446meaning of its contents regarding character classes, case mapping, etc.
447This should probably emit a warning (at least).
448
449This task is incremental - even a little bit of work on it will help.
e50bb9a1 450
cd793d32 451=head2 autovivification
e50bb9a1 452
cd793d32 453Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
e50bb9a1 454
0bdfc961 455This task is incremental - even a little bit of work on it will help.
e50bb9a1 456
0bdfc961 457=head2 Unicode in Filenames
e50bb9a1 458
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459chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
460opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
461system, truncate, unlink, utime, -X. All these could potentially accept
462Unicode filenames either as input or output (and in the case of system
463and qx Unicode in general, as input or output to/from the shell).
464Whether a filesystem - an operating system pair understands Unicode in
465filenames varies.
e50bb9a1 466
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467Known combinations that have some level of understanding include
468Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
469OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
470create Unicode filenames, what forms of Unicode are accepted and used
471(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
472and so on, varies. Finding the right level of interfacing to Perl
473requires some thought. Remember that an OS does not implicate a
474filesystem.
e50bb9a1 475
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476(The Windows -C command flag "wide API support" has been at least
477temporarily retired in 5.8.1, and the -C has been repurposed, see
478L<perlrun>.)
969e704b 479
0bdfc961 480=head2 Unicode in %ENV
969e704b 481
0bdfc961 482Currently the %ENV entries are always byte strings.
e50bb9a1 483
0bdfc961 484=head2 use less 'memory'
e50bb9a1 485
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486Investigate trade offs to switch out perl's choices on memory usage.
487Particularly perl should be able to give memory back.
e50bb9a1 488
0bdfc961 489This task is incremental - even a little bit of work on it will help.
0abe3f7c 490
0bdfc961 491=head2 Re-implement C<:unique> in a way that is actually thread-safe
0abe3f7c 492
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493The old implementation made bad assumptions on several levels. A good 90%
494solution might be just to make C<:unique> work to share the string buffer
495of SvPVs. That way large constant strings can be shared between ithreads,
496such as the configuration information in F<Config>.
0abe3f7c 497
0bdfc961 498=head2 Make tainting consistent
0abe3f7c 499
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500Tainting would be easier to use if it didn't take documented shortcuts and
501allow taint to "leak" everywhere within an expression.
0abe3f7c 502
0bdfc961 503=head2 readpipe(LIST)
0abe3f7c 504
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505system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
506running a shell. readpipe() (the function behind qx//) could be similarly
507extended.
0abe3f7c 508
e50bb9a1 509
e50bb9a1 510
e50bb9a1 511
f86a8bc5 512
0bdfc961 513=head1 Tasks that need a knowledge of the interpreter
3298bd4d 514
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515These tasks would need C knowledge, and knowledge of how the interpreter works,
516or a willingness to learn.
3298bd4d 517
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518=head2 lexical pragmas
519
520Reimplement the mechanism of lexical pragmas to be more extensible. Fix
521current pragmas that don't work well (or at all) with lexical scopes or in
522run-time eval(STRING) (C<sort>, C<re>, C<encoding> for example). MJD has a
523preliminary patch that implements this.
0562c0e3 524
d10fc472 525=head2 Attach/detach debugger from running program
1626a787 526
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527The old perltodo notes "With C<gdb>, you can attach the debugger to a running
528program if you pass the process ID. It would be good to do this with the Perl
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529debugger on a running Perl program, although I'm not sure how it would be
530done." ssh and screen do this with named pipes in /tmp. Maybe we can too.
1626a787 531
0bdfc961 532=head2 inlining autoloaded constants
d10fc472 533
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534Currently the optimiser can inline constants when expressed as subroutines
535with prototype ($) that return a constant. Likewise, many packages wrapping
536C libraries export lots of constants as subroutines which are AUTOLOADed on
537demand. However, these have no prototypes, so can't be seen as constants by
538the optimiser. Some way of cheaply (low syntax, low memory overhead) to the
539perl compiler that a name is a constant would be great, so that it knows to
540call the AUTOLOAD routine at compile time, and then inline the constant.
80b46460 541
0bdfc961 542=head2 Constant folding
80b46460 543
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544The peephole optimiser should trap errors during constant folding, and give
545up on the folding, rather than bailing out at compile time. It is quite
546possible that the unfoldable constant is in unreachable code, eg something
547akin to C<$a = 0/0 if 0;>
548
549=head2 LVALUE functions for lists
550
551The old perltodo notes that lvalue functions don't work for list or hash
552slices. This would be good to fix.
553
554=head2 LVALUE functions in the debugger
555
556The old perltodo notes that lvalue functions don't work in the debugger. This
557would be good to fix.
558
559=head2 _ prototype character
560
561Study the possibility of adding a new prototype character, C<_>, meaning
562"this argument defaults to $_".
563
564=head2 @INC source filter to Filter::Simple
565
566The second return value from a sub in @INC can be a source filter. This isn't
567documented. It should be changed to use Filter::Simple, tested and documented.
568
569=head2 regexp optimiser optional
570
571The regexp optimiser is not optional. It should configurable to be, to allow
572its performance to be measured, and its bugs to be easily demonstrated.
573
574=head2 UNITCHECK
575
576Introduce a new special block, UNITCHECK, which is run at the end of a
577compilation unit (module, file, eval(STRING) block). This will correspond to
578the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
579O.pm/B.pm backend framework depends on it.
580
581=head2 optional optimizer
582
583Make the peephole optimizer optional. Currently it performs two tasks as
584it walks the optree - genuine peephole optimisations, and necessary fixups of
585ops. It would be good to find an efficient way to switch out the
586optimisations whilst keeping the fixups.
587
588=head2 You WANT *how* many
589
590Currently contexts are void, scalar and list. split has a special mechanism in
591place to pass in the number of return values wanted. It would be useful to
592have a general mechanism for this, backwards compatible and little speed hit.
593This would allow proposals such as short circuiting sort to be implemented
594as a module on CPAN.
595
596=head2 lexical aliases
597
598Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
599
600=head2 entersub XS vs Perl
601
602At the moment pp_entersub is huge, and has code to deal with entering both
603perl and XS subroutines. Subroutine implementations rarely change between
604perl and XS at run time, so investigate using 2 ops to enter subs (one for
605XS, one for perl) and swap between if a sub is redefined.
2810d901
NC
606
607=head2 Self ties
608
609self ties are currently illegal because they caused too many segfaults. Maybe
610the causes of these could be tracked down and self-ties on all types re-
611instated.
0bdfc961
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612
613=head2 Optimize away @_
614
615The old perltodo notes "Look at the "reification" code in C<av.c>".
616
617=head2 switch ops
618
619The old perltodo notes "Although we have C<Switch.pm> in core, Larry points to
620the dormant C<nswitch> and C<cswitch> ops in F<pp.c>; using these opcodes would
621be much faster."
622
623=head2 What hooks would assertions need?
624
625Assertions are in the core, and work. However, assertions needed to be added
626as a core patch, rather than an XS module in ext, or a CPAN module, because
627the core has no hooks in the necessary places. It would be useful to
628investigate what hooks would need to be added to make it possible to provide
629the full assertion support from a CPAN module, so that we aren't constraining
630the imagination of future CPAN authors.
631
632
633
634
635
636
637
638=head1 Big projects
639
640Tasks that will get your name mentioned in the description of the "Highlights
641of 5.10"
642
643=head2 make ithreads more robust
644
645Generally make ithreads more robust. See also L<iCOW>
646
647This task is incremental - even a little bit of work on it will help, and
648will be greatly appreciated.
649
650=head2 iCOW
651
652Sarathy and Arthur have a proposal for an improved Copy On Write which
653specifically will be able to COW new ithreads. If this can be implemented
654it would be a good thing.
655
656=head2 (?{...}) closures in regexps
657
658Fix (or rewrite) the implementation of the C</(?{...})/> closures.
659
660=head2 A re-entrant regexp engine
661
662This will allow the use of a regex from inside (?{ }), (??{ }) and
663(?(?{ })|) constructs.