perltodo


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/
       <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
   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/test.pl. 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 test.pl. Throw in the handy tainting
       subroutines.

   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.

   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 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 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.

   embed.pl/makedef.pl
       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.

   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

       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


               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
       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 PERL_DL_NONLAZY=1.

   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 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.

       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

       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
       <http://www.xray.mpe.mpg.de/mailing-
       lists/perl5-porters/2002-04/msg02380.html>

   -Duse32bit*

       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
       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 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
       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

   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?

       currently offers us)

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

   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

   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),

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 opcode.pl)

   decapsulation of smart match argument
       Currently "$foo ~~ $object" will die with the message "Smart matching a
       non-overloaded object breaks encapsulation". It would be nice to allow
       to bypass this by using explicitly the syntax "$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
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-09/msg00573.html
       <http://www.xray.mpe.mpg.de/mailing-
       lists/perl5-porters/2008-09/msg00573.html>

   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'

       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.
       http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2007-03/msg00481.html
       <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

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

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

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

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

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

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

   Optimize away @_
       The old perltodo notes "Look at the "reification" code in "av.c"".

   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.

       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
       <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
       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:

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

           use warnings;
           my $undef;

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

       would produce this output

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

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

       What might work is to have an optional line number in memory just
       before the BASEOP 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"
       and will be greatly appreciated.

       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.

   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.

   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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