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       perltodo - Perl TO-DO List


       This is a list of wishes for Perl. The most up to date version of this file is at

       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 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

       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

Tasks that only need Perl knowledge

   Migrate t/ from custom TAP generation
       Many tests below t/ still generate TAP by "hand", rather than using library functions. As
       explained in "TESTING" in perlhack, tests in t/ are written in a particular way to test
       that more complex constructions actually work before using them routinely. Hence they
       don't use "Test::More", but instead there is an intentionally simpler library, t/
       However, quite a few tests in t/ have not been refactored to use it. Refactoring any of
       these tests, one at a time, is a useful thing TODO.

       The subdirectories base, cmd and comp, that contain the most basic tests, should be
       excluded from this task.

   Automate perldelta generation
       The perldelta file accompanying each release summaries the major changes.  It's mostly
       manually generated currently, but some of that could be automated with a bit of perl,
       specifically the generation of

       Modules and Pragmata
       New Documentation
       New Tests

       See Porting/how_to_write_a_perldelta.pod for details.

   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 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

   Make ExtUtils::ParseXS use strict;
       lib/ExtUtils/ 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.

   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' 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

   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 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.

   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.
       There is a script 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, doesn't understand the C macros, so the rules about which symbols are present
       when is duplicated in Writing things twice is bad, m'kay.  It would be good to
       teach "" 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;
           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.

   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.

   enable lexical enabling/disabling of individual warnings
       Currently, warnings can only be enabled or disabled by category. There are times when it
       would be useful to quash a single warning, not a whole category.

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

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


               make perl


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

       ·   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

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


               make perl.gcov

           (instead of "make perl")

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

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

       ·   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 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 "" 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 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, and will fail in the same way as msvc or mingw builds or when using

   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.

       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
       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 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

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

       ·   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:

       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 5.14.

   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
       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
       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:

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

       (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

   -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
       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.

   Write an XS cookbook
       Create pod/perlxscookbook.pod with short, task-focused 'recipes' in XS that demonstrate
       common tasks and good practices.  (Some of these might be extracted from perlguts.) The
       target audience should be XS novices, who need more examples than perlguts but something
       less overwhelming than perlapi.  Recipes should provide "one pretty good way to do it"
       instead of TIMTOWTDI.

       Rather than focusing on interfacing Perl to C libraries, such a cookbook should probably
       focus on how to optimize Perl routines by re-writing them in XS.  This will likely be more
       motivating to those who mostly work in Perl but are looking to take the next step into XS.

       Deconstructing and explaining some simpler XS modules could be one way to bootstrap a
       cookbook.  (List::Util? Class::XSAccessor? Tree::Ternary_XS?)  Another option could be
       deconstructing the implementation of some simpler functions in op.c.

   Allow XSUBs to inline themselves as OPs
       For a simple XSUB, often the subroutine dispatch takes more time than the XSUB itself. The
       tokeniser already has the ability to inline constant subroutines - it would be good to
       provide a way to inline other subroutines.

       Specifically, simplest approach looks to be to allow an XSUB to provide an alternative
       implementation of itself as a custom OP. A new flag bit in "CvFLAGS()" would signal to the
       peephole optimiser to take an optree such as this:

           b  <@> leave[1 ref] vKP/REFC ->(end)
           1     <0> enter ->2
           2     <;> nextstate(main 1 -e:1) v:{ ->3
           a     <2> sassign vKS/2 ->b
           8        <1> entersub[t2] sKS/TARG,1 ->9
           -           <1> ex-list sK ->8
           3              <0> pushmark s ->4
           4              <$> const(IV 1) sM ->5
           6              <1> rv2av[t1] lKM/1 ->7
           5                 <$> gv(*a) s ->6
           -              <1> ex-rv2cv sK ->-
           7                 <$> gv(*x) s/EARLYCV ->8
           -        <1> ex-rv2sv sKRM*/1 ->a
           9           <$> gvsv(*b) s ->a

       perform the symbol table lookup of "rv2cv" and "gv(*x)", locate the pointer to the custom
       OP that provides the direct implementation, and re- write the optree something like:

           b  <@> leave[1 ref] vKP/REFC ->(end)
           1     <0> enter ->2
           2     <;> nextstate(main 1 -e:1) v:{ ->3
           a     <2> sassign vKS/2 ->b
           7        <1> custom_x -> 8
           -           <1> ex-list sK ->7
           3              <0> pushmark s ->4
           4              <$> const(IV 1) sM ->5
           6              <1> rv2av[t1] lKM/1 ->7
           5                 <$> gv(*a) s ->6
           -              <1> ex-rv2cv sK ->-
           -                 <$> ex-gv(*x) s/EARLYCV ->7
           -        <1> ex-rv2sv sKRM*/1 ->a
           8           <$> gvsv(*b) s ->a

       i.e. the gv(*) OP has been nulled and spliced out of the execution path, and the
       "entersub" OP has been replaced by the custom op.

       This approach should provide a measurable speed up to simple XSUBs inside tight loops.
       Initially one would have to write the OP alternative implementation by hand, but it's
       likely that this should be reasonably straightforward for the type of XSUB that would
       benefit the most. Longer term, once the run-time implementation is proven, it should be
       possible to progressively update ExtUtils::ParseXS to generate OP implementations for some

   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.

   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)

       For more information see the thread starting with this message:

       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

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

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

   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

   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.

       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.)

       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.

   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 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, "").

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 is controversial if the right way to avoid the confusion is to forbid labels with
       keyword names, or if it would be better to always treat bareword expressions after a
       "goto" as a label and never as a keyword.

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

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

   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.  In the regex engine there are
       especially many problems.  The swash data structure could be replaced my something better.
       Inversion lists and maps are likely candidates.  The whole Unicode database could be
       placed in-core for a huge speed-up.  Only minimal work was done on the optimizer when utf8
       was added, with the result that the synthetic start class often will fail to narrow down
       the possible choices when given non-Latin1 input.

   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.

   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

   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.

   "/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/ }

       <> for the

   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 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"".

   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
       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

   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 in reverse-execution order to get them contiguous in memory
       in execution order.

       See <>

       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 line 4.
           Use of uninitialized value in numeric eq (==) at 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 line 4.
           Use of uninitialized value $undef in addition (+) at 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
       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.

   Add "00dddd"
       It has been proposed that octal constants be specifiable through the syntax "0oddddd",
       parallel to the existing construct to specify hex constants 0xddddd

Big projects

       Tasks that will get your name mentioned in the description of the "Highlights of 5.14"

   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

       One bit would be to determine how to clone directory handles on systems without a "fchdir"
       function (in sv.c:Perl_dirp_dup).

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

       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.

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

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