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PERLTODO(1)			 Perl Programmers Reference Guide		      PERLTODO(1)

NAME
       perltodo - Perl TO-DO List

DESCRIPTION
       This is a list of wishes for Perl. The tasks we think are smaller or easier are listed
       first. Anyone is welcome to work on any of these, but it's a good idea to first contact
       perl5-porters@perl.org to avoid duplication of effort, and to learn from any previous
       attempts.  By all means contact a pumpking privately first if you prefer.

       Whilst patches to make the list shorter are most welcome, ideas to add to the list are
       also encouraged. Check the perl5-porters archives for past ideas, and any discussion about
       them. One set of archives may be found at:

	   http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/

       What can we offer you in return? Fame, fortune, and everlasting glory? Maybe not, but if
       your patch is incorporated, then we'll add your name to the AUTHORS file, which ships in
       the official distribution. How many other programming languages offer you 1 line of immor-
       tality?

Tasks that only need Perl knowledge
       Smartmatch design issues

       In 5.10.0 the smartmatch operator "~~" isn't working quite "right". But before we can fix
       the implementation, we need to define what "right" is.  The first problem is that Robin
       Houston implemented the Perl 6 smart match spec as of February 2006, when smart match was
       axiomatically symmetrical: <http://groups.google.com/group/perl.perl6.lan-
       guage/msg/bf2b486f089ad021>

       Since then the Perl 6 target moved, but the Perl 5 implementation did not.

       So it would be useful for someone to compare the Perl 6 smartmatch table as of February
       2006
       <http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=markup&pathrev=7615>
       and the current table <http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?revi-
       sion=14556&view=markup> and tabulate the differences in Perl 6. The annotated view of
       changes is <http://svn.perl.org/viewvc/perl6/doc/trunk/design/syn/S03.pod?view=annotate>
       and the diff is "svn diff -r7615:14556
       http://svn.perl.org/perl6/doc/trunk/design/syn/S03.pod" -- search for "=head1 Smart match-
       ing". (In theory viewvc can generate that, but in practice when I tried it hung forever, I
       assume "thinking")

       With that done and published, someone (else) can then map any changed Perl 6 semantics
       back to Perl 5, based on how the existing semantics map to Perl 5:
       <http://search.cpan.org/~rgarcia/perl-5.10.0/pod/perlsyn.pod#Smart_matching_in_detail>

       There are also some questions that need answering:

       o   How do you negate one?  (documentation issue) http://www.xray.mpe.mpg.de/mail-
	   ing-lists/perl5-porters/2008-01/msg00071.html

       o   Array behaviors http://www.xray.mpe.mpg.de/mail-
	   ing-lists/perl5-porters/2007-12/msg00799.html

	   * Should smart matches be symmetrical? (Perl 6 says no)

	   * Other differences between Perl 5 and Perl 6 smart match?

       o   Objects and smart match http://www.xray.mpe.mpg.de/mail-
	   ing-lists/perl5-porters/2007-12/msg00865.html

       Remove duplication of test setup.

       Schwern notes, that there's duplication of code - lots and lots of tests have some varia-
       tion on the big block of $Is_Foo checks.  We can safely put this into a file, change it to
       build an %Is hash and require it.  Maybe just put it into test.pl. Throw in the handy
       tainting subroutines.

       POD -> HTML conversion in the core still sucks

       Which is crazy given just how simple POD purports to be, and how simple HTML can be. It's
       not actually as simple as it sounds, particularly with the flexibility POD allows for
       "=item", but it would be good to improve the visual appeal of the HTML generated, and to
       avoid it having any validation errors. See also "make HTML install work", as the layout of
       installation tree is needed to improve the cross-linking.

       The addition of "Pod::Simple" and its related modules may make this task easier to com-
       plete.

       merge checkpods and podchecker

       pod/checkpods.PL (and "make check" in the pod/ subdirectory) implements a very basic check
       for pod files, but the errors it discovers aren't found by podchecker. Add this check to
       podchecker, get rid of checkpods and have "make check" use podchecker.

       Parallel testing

       (This probably impacts much more than the core: also the Test::Harness and TAP::* modules
       on CPAN.)

       All of the tests in t/ can now be run in parallel, if $ENV{TEST_JOBS} is set. However,
       tests within each directory in ext and lib are still run in series, with directories run
       in parallel. This is an adequate heuristic, but it might be possible to relax it further,
       and get more throughput. Specifically, it would be good to audit all of lib/*.t, and make
       them use "File::Temp".

       Make Schwern poorer

       We should have tests for everything. When all the core's modules are tested, Schwern has
       promised to donate to $500 to TPF. We may need volunteers to hold him upside down and
       shake vigorously in order to actually extract the cash.

       Improve the coverage of the core tests

       Use Devel::Cover to ascertain the core modules's test coverage, then add tests that are
       currently missing.

       test B

       A full test suite for the B module would be nice.

       Deparse inlined constants

       Code such as this

	   use constant PI => 4;
	   warn PI

       will currently deparse as

	   use constant ('PI', 4);
	   warn 4;

       because the tokenizer inlines the value of the constant subroutine "PI".  This allows var-
       ious compile time optimisations, such as constant folding and dead code elimination. Where
       these haven't happened (such as the example above) it ought be possible to make B::Deparse
       work out the name of the original constant, because just enough information survives in
       the symbol table to do this. Specifically, the same scalar is used for the constant in the
       optree as is used for the constant subroutine, so by iterating over all symbol tables and
       generating a mapping of SV address to constant name, it would be possible to provide
       B::Deparse with this functionality.

       A decent benchmark

       "perlbench" seems impervious to any recent changes made to the perl core. It would be use-
       ful to have a reasonable general benchmarking suite that roughly represented what current
       perl programs do, and measurably reported whether tweaks to the core improve, degrade or
       don't really affect performance, to guide people attempting to optimise the guts of perl.
       Gisle would welcome new tests for perlbench.

       fix tainting bugs

       Fix the bugs revealed by running the test suite with the "-t" switch (via "make
       test.taintwarn").

       Dual life everything

       As part of the "dists" plan, anything that doesn't belong in the smallest perl distribu-
       tion needs to be dual lifed. Anything else can be too. Figure out what changes would be
       needed to package that module and its tests up for CPAN, and do so. Test it with older
       perl releases, and fix the problems you find.

       To make a minimal perl distribution, it's useful to look at t/lib/commonsense.t.

       Bundle dual life modules in ext/

       For maintenance (and branch merging) reasons, it would be useful to move some architec-
       ture-independent dual-life modules from lib/ to ext/, if this has no negative impact on
       the build of perl itself.

       POSIX memory footprint

       Ilya observed that use POSIX; eats memory like there's no tomorrow, and at various times
       worked to cut it down. There is probably still fat to cut out - for example POSIX passes
       Exporter some very memory hungry data structures.

       embed.pl/makedef.pl

       There is a script embed.pl that generates several header files to prefix all of Perl's
       symbols in a consistent way, to provide some semblance of namespace support in "C". Func-
       tions are declared in embed.fnc, variables in interpvar.h. Quite a few of the functions
       and variables are conditionally declared there, using "#ifdef". However, embed.pl doesn't
       understand the C macros, so the rules about which symbols are present when is duplicated
       in makedef.pl. Writing things twice is bad, m'kay.  It would be good to teach "embed.pl"
       to understand the conditional compilation, and hence remove the duplication, and the mis-
       takes it has caused.

       use strict; and AutoLoad

       Currently if you write

	   package Whack;
	   use AutoLoader 'AUTOLOAD';
	   use strict;
	   1;
	   __END__
	   sub bloop {
	       print join (' ', No, strict, here), "!\n";
	   }

       then "use strict;" isn't in force within the autoloaded subroutines. It would be more con-
       sistent (and less surprising) to arrange for all lexical pragmas in force at the __END__
       block to be in force within each autoloaded subroutine.

       There's a similar problem with SelfLoader.

       profile installman

       The installman script is slow. All it is doing text processing, which we're told is some-
       thing Perl is good at. So it would be nice to know what it is doing that is taking so much
       CPU, and where possible address it.

Tasks that need a little sysadmin-type knowledge
       Or if you prefer, tasks that you would learn from, and broaden your skills base...

       make HTML install work

       There is an "installhtml" target in the Makefile. It's marked as "experimental". It would
       be good to get this tested, make it work reliably, and remove the "experimental" tag. This
       would include

       1   Checking that cross linking between various parts of the documentation works.  In par-
	   ticular that links work between the modules (files with POD in lib/) and the core doc-
	   umentation (files in pod/)

       2   Work out how to split "perlfunc" into chunks, preferably one per function group,
	   preferably with general case code that could be used elsewhere.  Challenges here are
	   correctly identifying the groups of functions that go together, and making the right
	   named external cross-links point to the right page. Things to be aware of are "-X",
	   groups such as "getpwnam" to "endservent", two or more "=items" giving the different
	   parameter lists, such as

	       =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
	       =item substr EXPR,OFFSET,LENGTH
	       =item substr EXPR,OFFSET

	   and different parameter lists having different meanings. (eg "select")

       compressed man pages

       Be able to install them. This would probably need a configure test to see how the system
       does compressed man pages (same directory/different directory?  same filename/different
       filename), as well as tweaking the installman script to compress as necessary.

       Add a code coverage target to the Makefile

       Make it easy for anyone to run Devel::Cover on the core's tests. The steps to do this man-
       ually are roughly

       o   do a normal "Configure", but include Devel::Cover as a module to install (see INSTALL
	   for how to do this)

       o
	       make perl

       o
	       cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness

       o   Process the resulting Devel::Cover database

       This just give you the coverage of the .pms. To also get the C level coverage you need to

       o   Additionally tell "Configure" to use the appropriate C compiler flags for "gcov"

       o
	       make perl.gcov

	   (instead of "make perl")

       o   After running the tests run "gcov" to generate all the .gcov files.	(Including down
	   in the subdirectories of ext/

       o   (From the top level perl directory) run "gcov2perl" on all the ".gcov" files to get
	   their stats into the cover_db directory.

       o   Then process the Devel::Cover database

       It would be good to add a single switch to "Configure" to specify that you wanted to per-
       form perl level coverage, and another to specify C level coverage, and have "Configure"
       and the Makefile do all the right things automatically.

       Make Config.pm cope with differences between built and installed perl

       Quite often vendors ship a perl binary compiled with their (pay-for) compilers.	People
       install a free compiler, such as gcc. To work out how to build extensions, Perl interro-
       gates %Config, so in this situation %Config describes compilers that aren't there, and
       extension building fails. This forces people into choosing between re-compiling perl them-
       selves using the compiler they have, or only using modules that the vendor ships.

       It would be good to find a way teach "Config.pm" about the installation setup, possibly
       involving probing at install time or later, so that the %Config in a binary distribution
       better describes the installed machine, when the installed machine differs from the build
       machine in some significant way.

       linker specification files

       Some platforms mandate that you provide a list of a shared library's external symbols to
       the linker, so the core already has the infrastructure in place to do this for generating
       shared perl libraries. My understanding is that the GNU toolchain can accept an optional
       linker specification file, and restrict visibility just to symbols declared in that file.
       It would be good to extend makedef.pl to support this format, and to provide a means
       within "Configure" to enable it. This would allow Unix users to test that the export list
       is correct, and to build a perl that does not pollute the global namespace with private
       symbols.

       Cross-compile support

       Currently "Configure" understands "-Dusecrosscompile" option. This option arranges for
       building "miniperl" for TARGET machine, so this "miniperl" is assumed then to be copied to
       TARGET machine and used as a replacement of full "perl" executable.

       This could be done little differently. Namely "miniperl" should be built for HOST and then
       full "perl" with extensions should be compiled for TARGET.  This, however, might require
       extra trickery for %Config: we have one config first for HOST and then another for TARGET.
       Tools like MakeMaker will be mightily confused.	Having around two different types of exe-
       cutables and libraries (HOST and TARGET) makes life interesting for Makefiles and shell
       (and Perl) scripts.  There is $Config{run}, normally empty, which can be used as an execu-
       tion wrapper.  Also note that in some cross-compilation/execution environments the HOST
       and the TARGET do not see the same filesystem(s), the $Config{run} may need to do some
       file/directory copying back and forth.

       roffitall

       Make pod/roffitall be updated by pod/buildtoc.

       Split "linker" from "compiler"

       Right now, Configure probes for two commands, and sets two variables:

       * "cc" (in cc.U)
	   This variable holds the name of a command to execute a C compiler which can resolve
	   multiple global references that happen to have the same name.  Usual values are cc and
	   gcc.  Fervent ANSI compilers may be called c89.  AIX has xlc.

       * "ld" (in dlsrc.U)
	   This variable indicates the program to be used to link libraries for dynamic loading.
	   On some systems, it is ld.  On ELF systems, it should be $cc.  Mostly, we'll try to
	   respect the hint file setting.

       There is an implicit historical assumption from around Perl5.000alpha something, that $cc
       is also the correct command for linking object files together to make an executable. This
       may be true on Unix, but it's not true on other platforms, and there are a maze of work
       arounds in other places (such as Makefile.SH) to cope with this.

       Ideally, we should create a new variable to hold the name of the executable linker pro-
       gram, probe for it in Configure, and centralise all the special case logic there or in
       hints files.

       A small bikeshed issue remains - what to call it, given that $ld is already taken
       (arguably for the wrong thing now, but on SunOS 4.1 it is the command for creating dynami-
       cally-loadable modules) and $link could be confused with the Unix command line executable
       of the same name, which does something completely different. Andy Dougherty makes the
       counter argument "In parrot, I tried to call the command used to link object files and
       libraries into an executable link, since that's what my vaguely-remembered DOS and VMS
       experience suggested. I don't think any real confusion has ensued, so it's probably a rea-
       sonable name for perl5 to use."

       "Alas, I've always worried that introducing it would make things worse, since now the mod-
       ule building utilities would have to look for $Config{link} and institute a fall-back plan
       if it weren't found."  Although I can see that as confusing, given that $Config{d_link} is
       true when (hard) links are available.

Tasks that need a little C knowledge
       These tasks would need a little C knowledge, but don't need any specific background or
       experience with XS, or how the Perl interpreter works

       Weed out needless PERL_UNUSED_ARG

       The C code uses the macro "PERL_UNUSED_ARG" to stop compilers warning about unused argu-
       ments. Often the arguments can't be removed, as there is an external constraint that
       determines the prototype of the function, so this approach is valid. However, there are
       some cases where "PERL_UNUSED_ARG" could be removed. Specifically

       o   The prototypes of (nearly all) static functions can be changed

       o   Unused arguments generated by short cut macros are wasteful - the short cut macro used
	   can be changed.

       Modernize the order of directories in @INC

       The way @INC is laid out by default, one cannot upgrade core (dual-life) modules without
       overwriting files. This causes problems for binary package builders.  One possible pro-
       posal is laid out in this message: <http://www.xray.mpe.mpg.de/mail-
       ing-lists/perl5-porters/2002-04/msg02380.html>.

       -Duse32bit*

       Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.  On these systems,
       it might be the default compilation mode, and there is currently no guarantee that passing
       no use64bitall option to the Configure process will build a 32bit perl. Implementing
       -Duse32bit* options would be nice for perl 5.12.

       Make it clear from -v if this is the exact official release

       Currently perl from "p4"/"rsync" ships with a patchlevel.h file that usually defines one
       local patch, of the form "MAINT12345" or "RC1". The output of perl -v doesn't report that
       a perl isn't an official release, and this information can get lost in bugs reports.
       Because of this, the minor version isn't bumped up until RC time, to minimise the possi-
       bility of versions of perl escaping that believe themselves to be newer than they actually
       are.

       It would be useful to find an elegant way to have the "this is an interim maintenance
       release" or "this is a release candidate" in the terse -v output, and have it so that it's
       easy for the pumpking to remove this just as the release tarball is rolled up. This way
       the version pulled out of rsync would always say "I'm a development release" and it would
       be safe to bump the reported minor version as soon as a release ships, which would aid
       perl developers.

       This task is really about thinking of an elegant way to arrange the C source such that
       it's trivial for the Pumpking to flag "this is an official release" when making a tarball,
       yet leave the default source saying "I'm not the official release".

       Profile Perl - am I hot or not?

       The Perl source code is stable enough that it makes sense to profile it, identify and
       optimise the hotspots. It would be good to measure the performance of the Perl interpreter
       using free tools such as cachegrind, gprof, and dtrace, and work to reduce the bottlenecks
       they reveal.

       As part of this, the idea of pp_hot.c is that it contains the hot ops, the ops that are
       most commonly used. The idea is that by grouping them, their object code will be adjacent
       in the executable, so they have a greater chance of already being in the CPU cache (or
       swapped in) due to being near another op already in use.

       Except that it's not clear if these really are the most commonly used ops. So as part of
       exercising your skills with coverage and profiling tools you might want to determine what
       ops really are the most commonly used. And in turn suggest evictions and promotions to
       achieve a better pp_hot.c.

       One piece of Perl code that might make a good testbed is installman.

       Allocate OPs from arenas

       Currently all new OP structures are individually malloc()ed and free()d.  All "malloc"
       implementations have space overheads, and are now as fast as custom allocates so it would
       both use less memory and less CPU to allocate the various OP structures from arenas. The
       SV arena code can probably be re-used for this.

       Note that Configuring perl with "-Accflags=-DPL_OP_SLAB_ALLOC" will use Perl_Slab_alloc()
       to pack optrees into a contiguous block, which is probably superior to the use of OP are-
       nas, esp. from a cache locality standpoint.  See "Profile Perl - am I hot or not?".

       Improve win32/wince.c

       Currently, numerous functions look virtually, if not completely, identical in both
       "win32/wince.c" and "win32/win32.c" files, which can't be good.

       Use secure CRT functions when building with VC8 on Win32

       Visual C++ 2005 (VC++ 8.x) deprecated a number of CRT functions on the basis that they
       were "unsafe" and introduced differently named secure versions of them as replacements,
       e.g. instead of writing

	   FILE* f = fopen(__FILE__, "r");

       one should now write

	   FILE* f;
	   errno_t err = fopen_s(&f, __FILE__, "r");

       Currently, the warnings about these deprecations have been disabled by adding
       -D_CRT_SECURE_NO_DEPRECATE to the CFLAGS. It would be nice to remove that warning suppres-
       sant and actually make use of the new secure CRT functions.

       There is also a similar issue with POSIX CRT function names like fileno having been depre-
       cated in favour of ISO C++ conformant names like _fileno. These warnings are also cur-
       rently suppressed by adding -D_CRT_NONSTDC_NO_DEPRECATE. It might be nice to do as Micro-
       soft suggest here too, although, unlike the secure functions issue, there is presumably
       little or no benefit in this case.

       Fix POSIX::access() and chdir() on Win32

       These functions currently take no account of DACLs and therefore do not behave correctly
       in situations where access is restricted by DACLs (as opposed to the read-only attribute).

       Furthermore, POSIX::access() behaves differently for directories having the read-only
       attribute set depending on what CRT library is being used. For example, the _access()
       function in the VC6 and VC7 CRTs (wrongly) claim that such directories are not writable,
       whereas in fact all directories are writable unless access is denied by DACLs. (In the
       case of directories, the read-only attribute actually only means that the directory cannot
       be deleted.) This CRT bug is fixed in the VC8 and VC9 CRTs (but, of course, the directory
       may still not actually be writable if access is indeed denied by DACLs).

       For the chdir() issue, see ActiveState bug #74552: http://bugs.actives-
       tate.com/show_bug.cgi?id=74552

       Therefore, DACLs should be checked both for consistency across CRTs and for the correct
       answer.

       (Note that perl's -w operator should not be modified to check DACLs. It has been written
       so that it reflects the state of the read-only attribute, even for directories (whatever
       CRT is being used), for symmetry with chmod().)

       strcat(), strcpy(), strncat(), strncpy(), sprintf(), vsprintf()

       Maybe create a utility that checks after each libperl.a creation that none of the above
       (nor sprintf(), vsprintf(), or *SHUDDER* gets()) ever creep back to libperl.a.

	 nm libperl.a | ./miniperl -alne '$o = $F[0] if /:$/; print "$o $F[1]" if $F[0] eq "U" && $F[1] =~ /^(?:strn?c(?:at|py)|v?sprintf|gets)$/'

       Note, of course, that this will only tell whether your platform is using those naughty
       interfaces.

       -D_FORTIFY_SOURCE=2, -fstack-protector

       Recent glibcs support "-D_FORTIFY_SOURCE=2" and recent gcc (4.1 onwards?) supports
       "-fstack-protector", both of which give protection against various kinds of buffer over-
       flow problems.  These should probably be used for compiling Perl whenever available, Con-
       figure and/or hints files should be adjusted to probe for the availability of these fea-
       tures and enable them as appropriate.

       Arenas for GPs? For MAGIC?

       "struct gp" and "struct magic" are both currently allocated by "malloc".  It might be a
       speed or memory saving to change to using arenas. Or it might not. It would need some
       suitable benchmarking first. In particular, "GP"s can probably be changed with minimal
       compatibility impact (probably nothing outside of the core, or even outside of gv.c allo-
       cates them), but they probably aren't allocated/deallocated often enough for a speed sav-
       ing. Whereas "MAGIC" is allocated/deallocated more often, but in turn, is also something
       more externally visible, so changing the rules here may bite external code.

       Shared arenas

       Several SV body structs are now the same size, notably PVMG and PVGV, PVAV and PVHV, and
       PVCV and PVFM. It should be possible to allocate and return same sized bodies from the
       same actual arena, rather than maintaining one arena for each. This could save 4-6K per
       thread, of memory no longer tied up in the not-yet-allocated part of an arena.

Tasks that need a knowledge of XS
       These tasks would need C knowledge, and roughly the level of knowledge of the perl API
       that comes from writing modules that use XS to interface to C.

       investigate removing int_macro_int from POSIX.xs

       As a hang over from the original "constant" implementation, POSIX.xs contains a function
       "int_macro_int" which in conjunction with "AUTOLOAD" is used to wrap the C functions "WEX-
       ITSTATUS", "WIFEXITED", "WIFSIGNALED", "WIFSTOPPED", "WSTOPSIG" and "WTERMSIG". It's prob-
       ably worth replacing this complexity with 5 simple direct wrappings of those 5 functions.

       However, it would be interesting if someone could measure the memory usage before and
       after, both for the case of "use POSIX();" and the case of actually calling the Perl space
       functions.

       safely supporting POSIX SA_SIGINFO

       Some years ago Jarkko supplied patches to provide support for the POSIX SA_SIGINFO feature
       in Perl, passing the extra data to the Perl signal handler.

       Unfortunately, it only works with "unsafe" signals, because under safe signals, by the
       time Perl gets to run the signal handler, the extra information has been lost. Moreover,
       it's not easy to store it somewhere, as you can't call mutexs, or do anything else fancy,
       from inside a signal handler.

       So it strikes me that we could provide safe SA_SIGINFO support

       1   Provide global variables for two file descriptors

       2   When the first request is made via "sigaction" for "SA_SIGINFO", create a pipe, store
	   the reader in one, the writer in the other

       3   In the "safe" signal handler ("Perl_csighandler()"/"S_raise_signal()"), if the "sig-
	   info_t" pointer non-"NULL", and the writer file handle is open,

	   1	   serialise signal number, "struct siginfo_t" (or at least the parts we care
		   about) into a small auto char buff

	   2	   "write()" that (non-blocking) to the writer fd

		   1	       if it writes 100%, flag the signal in a counter of "signals on the
			       pipe" akin to the current per-signal-number counts

		   2	       if it writes 0%, assume the pipe is full. Flag the data as lost?

		   3	       if it writes partially, croak a panic, as your OS is broken.

       4   in the regular "PERL_ASYNC_CHECK()" processing, if there are "signals on the pipe",
	   read the data out, deserialise, build the Perl structures on the stack (code in
	   "Perl_sighandler()", the "unsafe" handler), and call as usual.

       I think that this gets us decent "SA_SIGINFO" support, without the current risk of running
       Perl code inside the signal handler context. (With all the dangers of things like "malloc"
       corruption that that currently offers us)

       For more information see the thread starting with this message:
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-03/msg00305.html

       autovivification

       Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;

       This task is incremental - even a little bit of work on it will help.

       Unicode in Filenames

       chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open, opendir, qx, readdir,
       readlink, rename, rmdir, stat, symlink, sysopen, system, truncate, unlink, utime, -X.  All
       these could potentially accept Unicode filenames either as input or output (and in the
       case of system and qx Unicode in general, as input or output to/from the shell).  Whether
       a filesystem - an operating system pair understands Unicode in filenames varies.

       Known combinations that have some level of understanding include Microsoft NTFS, Apple
       HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac OS X), NFS v4 is rumored to be Unicode, and
       of course Plan 9.  How to create Unicode filenames, what forms of Unicode are accepted and
       used (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used, and so on,
       varies.	Finding the right level of interfacing to Perl requires some thought.  Remember
       that an OS does not implicate a filesystem.

       (The Windows -C command flag "wide API support" has been at least temporarily retired in
       5.8.1, and the -C has been repurposed, see perlrun.)

       Most probably the right way to do this would be this: "Virtualize operating system
       access".

       Unicode in %ENV

       Currently the %ENV entries are always byte strings.  See "Virtualize operating system
       access".

       Unicode and glob()

       Currently glob patterns and filenames returned from File::Glob::glob() are always byte
       strings.  See "Virtualize operating system access".

       Unicode and lc/uc operators

       Some built-in operators ("lc", "uc", etc.) behave differently, based on what the internal
       encoding of their argument is. That should not be the case. Maybe add a pragma to switch
       behaviour.

       use less 'memory'

       Investigate trade offs to switch out perl's choices on memory usage.  Particularly perl
       should be able to give memory back.

       This task is incremental - even a little bit of work on it will help.

       Re-implement ":unique" in a way that is actually thread-safe

       The old implementation made bad assumptions on several levels. A good 90% solution might
       be just to make ":unique" work to share the string buffer of SvPVs. That way large con-
       stant strings can be shared between ithreads, such as the configuration information in
       Config.

       Make tainting consistent

       Tainting would be easier to use if it didn't take documented shortcuts and allow taint to
       "leak" everywhere within an expression.

       readpipe(LIST)

       system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid running a shell. read-
       pipe() (the function behind qx//) could be similarly extended.

       Audit the code for destruction ordering assumptions

       Change 25773 notes

	   /* Need to check SvMAGICAL, as during global destruction it may be that
	      AvARYLEN(av) has been freed before av, and hence the SvANY() pointer
	      is now part of the linked list of SV heads, rather than pointing to
	      the original body.  */
	   /* FIXME - audit the code for other bugs like this one.  */

       adding the "SvMAGICAL" check to

	   if (AvARYLEN(av) && SvMAGICAL(AvARYLEN(av))) {
	       MAGIC *mg = mg_find (AvARYLEN(av), PERL_MAGIC_arylen);

       Go through the core and look for similar assumptions that SVs have particular types, as
       all bets are off during global destruction.

       Extend PerlIO and PerlIO::Scalar

       PerlIO::Scalar doesn't know how to truncate().  Implementing this would require extending
       the PerlIO vtable.

       Similarly the PerlIO vtable doesn't know about formats (write()), or about stat(), or
       chmod()/chown(), utime(), or flock().

       (For PerlIO::Scalar it's hard to see what e.g. mode bits or ownership would mean.)

       PerlIO doesn't do directories or symlinks, either: mkdir(), rmdir(), opendir(),
       closedir(), seekdir(), rewinddir(), glob(); symlink(), readlink().

       See also "Virtualize operating system access".

       -C on the #! line

       It should be possible to make -C work correctly if found on the #! line, given that all
       perl command line options are strict ASCII, and -C changes only the interpretation of non-
       ASCII characters, and not for the script file handle. To make it work needs some investi-
       gation of the ordering of function calls during startup, and (by implication) a bit of
       tweaking of that order.

       Propagate const outwards from Perl_moreswitches()

       Change 32057 changed the parameter and return value of "Perl_moreswitches()" from <char *>
       to <const char *>. It should now be possible to propagate const-correctness outwards to
       "S_parse_body()", "Perl_moreswitches()" and "Perl_yylex()".

       Duplicate logic in S_method_common() and Perl_gv_fetchmethod_autoload()

       A comment in "S_method_common" notes

	       /* This code tries to figure out just what went wrong with
		  gv_fetchmethod.  It therefore needs to duplicate a lot of
		  the internals of that function.  We can't move it inside
		  Perl_gv_fetchmethod_autoload(), however, since that would
		  cause UNIVERSAL->can("NoSuchPackage::foo") to croak, and we
		  don't want that.
	       */

       If "Perl_gv_fetchmethod_autoload" gets rewritten to take (more) flag bits, then it ought
       to be possible to move the logic from "S_method_common" to the "right" place. When making
       this change it would probably be good to also pass in at least the method name length, if
       not also pre-computed hash values when known. (I'm contemplating a plan to pre-compute
       hash values for common fixed strings such as "ISA" and pass them in to functions.)

       Organize error messages

       Perl's diagnostics (error messages, see perldiag) could use reorganizing and formalizing
       so that each error message has its stable-for-all-eternity unique id, categorized by
       severity, type, and subsystem.  (The error messages would be listed in a datafile outside
       of the Perl source code, and the source code would only refer to the messages by the id.)
       This clean-up and regularizing should apply for all croak() messages.

       This would enable all sorts of things: easier translation/localization of the messages
       (though please do keep in mind the caveats of Locale::Maketext about too straightforward
       approaches to translation), filtering by severity, and instead of grepping for a particu-
       lar error message one could look for a stable error id.	(Of course, changing the error
       messages by default would break all the existing software depending on some particular
       error message...)

       This kind of functionality is known as message catalogs.  Look for inspiration for example
       in the catgets() system, possibly even use it if available-- but only if available, all
       platforms will not have catgets().

       For the really pure at heart, consider extending this item to cover also the warning mes-
       sages (see perllexwarn, "warnings.pl").

Tasks that need a knowledge of the interpreter
       These tasks would need C knowledge, and knowledge of how the interpreter works, or a will-
       ingness to learn.

       error reporting of [$a ; $b]

       Using ";" inside brackets is a syntax error, and we don't propose to change that by giving
       it any meaning. However, it's not reported very helpfully:

	   $ perl -e '$a = [$b; $c];'
	   syntax error at -e line 1, near "$b;"
	   syntax error at -e line 1, near "$c]"
	   Execution of -e aborted due to compilation errors.

       It should be possible to hook into the tokeniser or the lexer, so that when a ";" is
       parsed where it is not legal as a statement terminator (ie inside "{}" used as a hashref,
       "[]" or "()") it issues an error something like ';' isn't legal inside an expression - if
       you need multiple statements use a do {...} block. See the thread starting at
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html

       UTF-8 revamp

       The handling of Unicode is unclean in many places. For example, the regexp engine matches
       in Unicode semantics whenever the string or the pattern is flagged as UTF-8, but that
       should not be dependent on an internal storage detail of the string. Likewise, case fold-
       ing behaviour is dependent on the UTF8 internal flag being on or off.

       Properly Unicode safe tokeniser and pads.

       The tokeniser isn't actually very UTF-8 clean. "use utf8;" is a hack - variable names are
       stored in stashes as raw bytes, without the utf-8 flag set. The pad API only takes a "char
       *" pointer, so that's all bytes too. The tokeniser ignores the UTF-8-ness of "PL_rsfp", or
       any SVs returned from source filters.  All this could be fixed.

       state variable initialization in list context

       Currently this is illegal:

	   state ($a, $b) = foo();

       In Perl 6, "state ($a) = foo();" and "(state $a) = foo();" have different semantics, which
       is tricky to implement in Perl 5 as currently they produce the same opcode trees. The Perl
       6 design is firm, so it would be good to implement the necessary code in Perl 5. There are
       comments in "Perl_newASSIGNOP()" that show the code paths taken by various assignment con-
       structions involving state variables.

       Implement $value ~~ 0 .. $range

       It would be nice to extend the syntax of the "~~" operator to also understand numeric (and
       maybe alphanumeric) ranges.

       A does() built-in

       Like ref(), only useful. It would call the "DOES" method on objects; it would also tell
       whether something can be dereferenced as an array/hash/etc., or used as a regexp, etc.
       <http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html>

       Tied filehandles and write() don't mix

       There is no method on tied filehandles to allow them to be called back by formats.

       Attach/detach debugger from running program

       The old perltodo notes "With "gdb", you can attach the debugger to a running program if
       you pass the process ID. It would be good to do this with the Perl debugger on a running
       Perl program, although I'm not sure how it would be done." ssh and screen do this with
       named pipes in /tmp. Maybe we can too.

       Optimize away empty destructors

       Defining an empty DESTROY method might be useful (notably in AUTOLOAD-enabled classes),
       but it's still a bit expensive to call. That could probably be optimized.

       LVALUE functions for lists

       The old perltodo notes that lvalue functions don't work for list or hash slices. This
       would be good to fix.

       LVALUE functions in the debugger

       The old perltodo notes that lvalue functions don't work in the debugger. This would be
       good to fix.

       regexp optimiser optional

       The regexp optimiser is not optional. It should configurable to be, to allow its perfor-
       mance to be measured, and its bugs to be easily demonstrated.

       delete &function

       Allow to delete functions. One can already undef them, but they're still in the stash.

       "/w" regex modifier

       That flag would enable to match whole words, and also to interpolate arrays as alterna-
       tions. With it, "/P/w" would be roughly equivalent to:

	   do { local $"='|'; /\b(?:P)\b/ }

       See <http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-01/msg00400.html> for the
       discussion.

       optional optimizer

       Make the peephole optimizer optional. Currently it performs two tasks as it walks the
       optree - genuine peephole optimisations, and necessary fixups of ops. It would be good to
       find an efficient way to switch out the optimisations whilst keeping the fixups.

       You WANT *how* many

       Currently contexts are void, scalar and list. split has a special mechanism in place to
       pass in the number of return values wanted. It would be useful to have a general mechanism
       for this, backwards compatible and little speed hit.  This would allow proposals such as
       short circuiting sort to be implemented as a module on CPAN.

       lexical aliases

       Allow lexical aliases (maybe via the syntax "my \$alias = \$foo".

       entersub XS vs Perl

       At the moment pp_entersub is huge, and has code to deal with entering both perl and XS
       subroutines. Subroutine implementations rarely change between perl and XS at run time, so
       investigate using 2 ops to enter subs (one for XS, one for perl) and swap between if a sub
       is redefined.

       Self-ties

       Self-ties are currently illegal because they caused too many segfaults. Maybe the causes
       of these could be tracked down and self-ties on all types reinstated.

       Optimize away @_

       The old perltodo notes "Look at the "reification" code in "av.c"".

       The yada yada yada operators

       Perl 6's Synopsis 3 says:

       The ... operator is the "yada, yada, yada" list operator, which is used as the body in
       function prototypes. It complains bitterly (by calling fail) if it is ever executed. Vari-
       ant ??? calls warn, and !!! calls die.

       Those would be nice to add to Perl 5. That could be done without new ops.

       Virtualize operating system access

       Implement a set of "vtables" that virtualizes operating system access (open(), mkdir(),
       unlink(), readdir(), getenv(), etc.)  At the very least these interfaces should take SVs
       as "name" arguments instead of bare char pointers; probably the most flexible and extensi-
       ble way would be for the Perl-facing interfaces to accept HVs.  The system needs to be
       per-operating-system and per-file-system hookable/filterable, preferably both from XS and
       Perl level ("Files and Filesystems" in perlport is good reading at this point, in fact,
       all of perlport is.)

       This has actually already been implemented (but only for Win32), take a look at iperlsys.h
       and win32/perlhost.h.  While all Win32 variants go through a set of "vtables" for operat-
       ing system access, non-Win32 systems currently go straight for the POSIX/UNIX-style sys-
       tem/library call.  Similar system as for Win32 should be implemented for all platforms.
       The existing Win32 implementation probably does not need to survive alongside this pro-
       posed new implementation, the approaches could be merged.

       What would this give us?  One often-asked-for feature this would enable is using Unicode
       for filenames, and other "names" like %ENV, usernames, hostnames, and so forth.	(See
       "When Unicode Does Not Happen" in perlunicode.)

       But this kind of virtualization would also allow for things like virtual filesystems, vir-
       tual networks, and "sandboxes" (though as long as dynamic loading of random object code is
       allowed, not very safe sandboxes since external code of course know not of Perl's vta-
       bles).  An example of a smaller "sandbox" is that this feature can be used to implement
       per-thread working directories: Win32 already does this.

       See also "Extend PerlIO and PerlIO::Scalar".

       Investigate PADTMP hash pessimisation

       The peephole optimier converts constants used for hash key lookups to shared hash key
       scalars. Under ithreads, something is undoing this work.  See
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-09/msg00793.html

       Store the current pad in the OP slab allocator

       Currently we leak ops in various cases of parse failure. I suggested that we could solve
       this by always using the op slab allocator, and walking it to free ops. Dave comments that
       as some ops are already freed during optree creation one would have to mark which ops are
       freed, and not double free them when walking the slab. He notes that one problem with this
       is that for some ops you have to know which pad was current at the time of allocation,
       which does change. I suggested storing a pointer to the current pad in the memory allo-
       cated for the slab, and swapping to a new slab each time the pad changes. Dave thinks that
       this would work.

       repack the optree

       Repacking the optree after execution order is determined could allow removal of NULL ops,
       and optimal ordering of OPs with respect to cache-line filling.	The slab allocator could
       be reused for this purpose.  I think that the best way to do this is to make it an
       optional step just before the completed optree is attached to anything else, and to use
       the slab allocator unchanged, so that freeing ops is identical whether or not this step
       runs.  Note that the slab allocator allocates ops downwards in memory, so one would have
       to actually "allocate" the ops in reverse-execution order to get them contiguous in memory
       in execution order.

       See http://www.nntp.perl.org/group/perl.perl5.porters/2007/12/msg131975.html

       Note that running this copy, and then freeing all the old location ops would cause their
       slabs to be freed, which would eliminate possible memory wastage if the previous sugges-
       tion is implemented, and we swap slabs more frequently.

       eliminate incorrect line numbers in warnings

       This code

	   use warnings;
	   my $undef;

	   if ($undef == 3) {
	   } elsif ($undef == 0) {
	   }

       used to produce this output:

	   Use of uninitialized value in numeric eq (==) at wrong.pl line 4.
	   Use of uninitialized value in numeric eq (==) at wrong.pl line 4.

       where the line of the second warning was misreported - it should be line 5.  Rafael fixed
       this - the problem arose because there was no nextstate OP between the execution of the
       "if" and the "elsif", hence "PL_curcop" still reports that the currently executing line is
       line 4. The solution was to inject a nextstate OPs for each "elsif", although it turned
       out that the nextstate OP needed to be a nulled OP, rather than a live nextstate OP, else
       other line numbers became misreported. (Jenga!)

       The problem is more general than "elsif" (although the "elsif" case is the most common and
       the most confusing). Ideally this code

	   use warnings;
	   my $undef;

	   my $a = $undef + 1;
	   my $b
	     = $undef
	     + 1;

       would produce this output

	   Use of uninitialized value $undef in addition (+) at wrong.pl line 4.
	   Use of uninitialized value $undef in addition (+) at wrong.pl line 7.

       (rather than lines 4 and 5), but this would seem to require every OP to carry (at least)
       line number information.

       What might work is to have an optional line number in memory just before the BASEOP struc-
       ture, with a flag bit in the op to say whether it's present.  Initially during compile
       every OP would carry its line number. Then add a late pass to the optimiser (potentially
       combined with "repack the optree") which looks at the two ops on every edge of the graph
       of the execution path. If the line number changes, flags the destination OP with this
       information.  Once all paths are traced, replace every op with the flag with a nextstate-
       light op (that just updates "PL_curcop"), which in turn then passes control on to the true
       op. All ops would then be replaced by variants that do not store the line number. (Which,
       logically, why it would work best in conjunction with "repack the optree", as that is
       already copying/reallocating all the OPs)

       (Although I should note that we're not certain that doing this for the general case is
       worth it)

       optimize tail-calls

       Tail-calls present an opportunity for broadly applicable optimization; anywhere that
       "return foo(...)" is called, the outer return can be replaced by a goto, and foo will
       return directly to the outer caller, saving (conservatively) 25% of perl's call&return
       cost, which is relatively higher than in C.  The scheme language is known to do this heav-
       ily.  B::Concise provides good insight into where this optimization is possible, ie any-
       where entersub,leavesub op-sequence occurs.

	perl -MO=Concise,-exec,a,b,-main -e 'sub a{ 1 }; sub b {a()}; b(2)'

       Bottom line on this is probably a new pp_tailcall function which combines the code in
       pp_entersub, pp_leavesub.  This should probably be done 1st in XS, and using B::Generate
       to patch the new OP into the optrees.

Big projects
       Tasks that will get your name mentioned in the description of the "Highlights of 5.12"

       make ithreads more robust

       Generally make ithreads more robust. See also "iCOW"

       This task is incremental - even a little bit of work on it will help, and will be greatly
       appreciated.

       One bit would be to write the missing code in sv.c:Perl_dirp_dup.

       Fix Perl_sv_dup, et al so that threads can return objects.

       iCOW

       Sarathy and Arthur have a proposal for an improved Copy On Write which specifically will
       be able to COW new ithreads. If this can be implemented it would be a good thing.

       (?{...}) closures in regexps

       Fix (or rewrite) the implementation of the "/(?{...})/" closures.

       A re-entrant regexp engine

       This will allow the use of a regex from inside (?{ }), (??{ }) and (?(?{ })|) constructs.

       Add class set operations to regexp engine

       Apparently these are quite useful. Anyway, Jeffery Friedl wants them.

       demerphq has this on his todo list, but right at the bottom.

perl v5.8.9				    2007-11-17				      PERLTODO(1)
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