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NAME
       perltodo - Perl TO-DO List

DESCRIPTION
       This is a list of wishes for Perl. The most up to date
       version of this file is at
       http://perl5.git.perl.org/perl.git/blob_plain/HEAD:/pod/perltodo.pod

       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
       immortality?

Tasks that only need Perl knowledge
   Remove macperl references from tests
       MacPerl is gone. The tests don't need to be there.

   Remove duplication of test setup.
       Schwern notes, that there's duplication of code - lots and
       lots of tests have some variation 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 complete.




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   Make ExtUtils::ParseXS use strict;
       lib/ExtUtils/ParseXS.pm contains this line

           # use strict;  # One of these days...

       Simply uncomment it, and fix all the resulting issues :-)

       The more practical approach, to break the task down into
       manageable chunks, is to work your way though the code
       from bottom to top, or if necessary adding extra "{ ... }"
       blocks, and turning on strict within them.

   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.

   A decent benchmark
       "perlbench" seems impervious to any recent changes made to
       the perl core. It would be useful 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 distribution needs to be dual lifed.
       Anything else can be too. Figure out what changes would be



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       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 architecture-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".
       Functions 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
       mistakes 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 consistent (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.





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   profile installman
       The installman script is slow. All it is doing text
       processing, which we're told is something 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 particular that links
           work between the modules (files with POD in lib/) and
           the core documentation (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 manually are roughly

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

       o




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               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 perform 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
       interrogates %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 themselves 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.




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   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 executables 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 execution 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:

       o   "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.

       o   "ld" (in dlsrc.U)

           This variable indicates the program to be used to link



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           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 program, 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
       dynamically-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 reasonable name
       for perl5 to use."

       "Alas, I've always worried that introducing it would make
       things worse, since now the module 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.

   Configure Windows using PowerShell
       Currently, Windows uses hard-coded config files based to
       build the config.h for compiling Perl.  Makefiles are also
       hard-coded and need to be hand edited prior to building
       Perl. While this makes it easy to create a perl.exe that
       works across multiple Windows versions, being able to
       accurately configure a perl.exe for a specific Windows
       versions and VS C++ would be a nice enhancement.  With
       PowerShell available on Windows XP and up, this may now be
       possible.  Step 1 might be to investigate whether this is
       possible and use this to clean up our current makefile
       situation.  Step 2 would be to see if there would be a way
       to use our existing metaconfig units to configure a
       Windows Perl or whether we go in a separate direction and
       make it so.  Of course, we all know what step 3 is.

   decouple -g and -DDEBUGGING
       Currently Configure automatically adds "-DDEBUGGING" to



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       the C compiler flags if it spots "-g" in the optimiser
       flags. The pre-processor directive "DEBUGGING" enables
       perl's command line <-D> options, but in the process makes
       perl slower. It would be good to disentangle this logic,
       so that C-level debugging with "-g" and Perl level
       debugging with "-D" can easily be enabled independently.

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 arguments. 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
       proposal is laid out in this message:
       <http://www.xray.mpe.mpg.de/mailing-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.

   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



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       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 arenas, 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
       suppressant 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 deprecated in favour of ISO
       C++ conformant names like _fileno. These warnings are also



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       currently suppressed by adding
       -D_CRT_NONSTDC_NO_DEPRECATE. It might be nice to do as
       Microsoft 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.activestate.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 overflow
       problems.  These should probably be used for compiling
       Perl whenever available, Configure and/or hints files
       should be adjusted to probe for the availability of these



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       features 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 allocates them), but they
       probably aren't allocated/deallocated often enough for a
       speed saving. 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.

   Remove the use of SVs as temporaries in dump.c
       dump.c contains debugging routines to dump out the
       contains of perl data structures, such as "SV"s, "AV"s and
       "HV"s. Currently, the dumping code uses "SV"s for its
       temporary buffers, which was a logical initial
       implementation choice, as they provide ready made memory
       handling.

       However, they also lead to a lot of confusion when it
       happens that what you're trying to debug is seen by the
       code in dump.c, correctly or incorrectly, as a temporary
       scalar it can use for a temporary buffer. It's also not
       possible to dump scalars before the interpreter is
       properly set up, such as during ithreads cloning. It would
       be good to progressively replace the use of scalars as
       string accumulation buffers with something much simpler,
       directly allocated by "malloc". The dump.c code is (or
       should be) only producing 7 bit US-ASCII, so output
       character sets are not an issue.

       Producing and proving an internal simple buffer allocation
       would make it easier to re-write the internals of the
       PerlIO subsystem to avoid using "SV"s for its buffers, use
       of which can cause problems similar to those of dump.c, at
       similar times.



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   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
           "siginfo_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)




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       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.





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   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 constant 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. readpipe() (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.)



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       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 investigation of the
       ordering of function calls during startup, and (by
       implication) a bit of tweaking of that order.

   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 particular 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



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       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 messages (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 willingness to learn.

   forbid labels with keyword names
       Currently "goto keyword" "computes" the label value:

           $ perl -e 'goto print'
           Can't find label 1 at -e line 1.

       It would be nice to forbid labels with keyword names, to
       avoid confusion.

   truncate() prototype
       The prototype of truncate() is currently $$. It should
       probably be "*$" instead. (This is changed in opcode.pl)

   decapsulation of smart match argument
       Currently "$foo ~~ $object" will die with the message
       "Smart matching a non-overloaded object breaks
       encapsulation". It would be nice to allow to bypass this
       by using explictly the syntax "$foo ~~ %$object" or "$foo
       ~~ @$object".

   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




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   lexicals used only once
       This warns:

           $ perl -we '$pie = 42'
           Name "main::pie" used only once: possible typo at -e line 1.

       This does not:

           $ perl -we 'my $pie = 42'

       Logically all lexicals used only once should warn, if the
       user asks for warnings.  An unworked RT ticket (#5087) has
       been open for almost seven years for this discrepancy.

   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 folding 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 constructions 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.



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       <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.

   Propagate compilation hints to the debugger
       Currently a debugger started with -dE on the command-line
       doesn't see the features enabled by -E. More generally
       hints ($^H and "%^H") aren't propagated to the debugger.
       Probably it would be a good thing to propagate hints from
       the innermost non-"DB::" scope: this would make code
       eval'ed in the debugger see the features (and strictures,
       etc.) currently in scope.

   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.

   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.

   regexp optimiser optional
       The regexp optimiser is not optional. It should
       configurable to be, to allow its performance 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 alternations. 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.




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   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. Variant ??? 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 extensible 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



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       operating system access, non-Win32 systems currently go
       straight for the POSIX/UNIX-style system/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 proposed 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, virtual 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 vtables).  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 optimiser 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 allocated 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



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       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
       suggestion 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.




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       (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 structure, 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 heavily.  B::Concise provides good insight into
       where this optimization is possible, ie anywhere
       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.

   "\N"
       It should be possible to add a "\N" regex assertion,
       meaning "every character except "\n"X independently of the
       context. That would of course imply that "\N" couldn't be
       followed by an opening "{".

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"




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       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.

Tasks for microperl
       [ Each and every one of these may be obsolete, but they
       were listed
         in the old Todo.micro file]

   make creating uconfig.sh automatic
   make creating Makefile.micro automatic
   do away with fork/exec/wait?
       (system, popen should be enough?)

   some of the uconfig.sh really needs to be probed (using cc) in
       buildtime:
       (uConfigure? :-) native datatype widths and endianness
       come to mind















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