


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


NAME
       perltodo - Perl TO-DO List

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

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

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

       What can we offer you in return? Fame, fortune, and ever-
       lasting glory? Maybe not, but if your patch is incorpo-
       rated, then we'll add your name to the AUTHORS file, which
       ships in the official distribution. How many other pro-
       gramming languages offer you 1 line of immortality?

The roadmap to 5.10
       The roadmap to 5.10 envisages feature based releases, as
       various items in this TODO are completed.

       Needed for a 5.9.4 release


       o   Review assertions. Review syntax to combine asser-
           tions. Assertions could take advantage of the lexical
           pragmas work. "What hooks would assertions need?"

       Needed for a 5.9.5 release


       * Implement "_ prototype character"
       * Implement "state variables"

       Needed for a 5.9.6 release

       Stabilisation. If all goes well, this will be the equiva-
       lent of a 5.10-beta.

Tasks that only need Perl knowledge
       common test code for timed bail out

       Write portable self destruct code for tests to stop them
       burning CPU in infinite loops. This needs to avoid using
       alarm, as some of the tests are testing alarm/sleep or
       timers.




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       POD -> HTML conversion in the core still sucks

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

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

       Parallel testing

       The core regression test suite is getting ever more com-
       prehensive, which has the side effect that it takes longer
       to run. This isn't so good. Investigate whether it would
       be feasible to give the harness script the option of run-
       ning sets of tests in parallel. This would be useful for
       tests in t/op/*.t and t/uni/*.t and maybe some sets of
       tests in lib/.

       Questions to answer

       1   How does screen layout work when you're running more
           than one test?

       2   How does the caller of test specify how many tests to
           run in parallel?

       3   How do setup/teardown tests identify themselves?

       Pugs already does parallel testing - can their approach be
       re-used?

       Make Schwern poorer

       We should have 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.

       See t/lib/1_compile.t for the 3 remaining modules that
       need tests.

       Improve the coverage of the core tests

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






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       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.

       Improving "threads::shared"

       Investigate whether "threads::shared" could share aggre-
       gates properly with only Perl level changes to shared.pm

       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.

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

       Relocatable perl

       The C level patches needed to create a relocatable perl
       binary are done, as is the work on Config.pm. All that's
       left to do is the "Configure" tweaking to let people spec-
       ify how they want to do the install.







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       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 "experimen-
       tal" 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, prefer-
           ably 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 "end-
           servent", 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 mean-
           ings. (eg "select")

       compressed man pages

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

       Add a code coverage target to the Makefile

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

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

       o
               make perl

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

       o   Process the resulting Devel::Cover database



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       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 "Config-
       ure" and the Makefile do all the right things automati-
       cally.

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

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

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

       make parallel builds work

       Currently parallel builds (such as "make -j3") don't work
       reliably. We believe that this is due to incomplete depen-
       dency specification in the Makefile.  It would be good if
       someone were able to track down the causes of these prob-
       lems, so that parallel builds worked properly.




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       linker specification files

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

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

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

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

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

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

       Tidy up global variables

       There's a note in intrpvar.h







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         /* These two variables are needed to preserve 5.8.x bincompat because
            we can't change function prototypes of two exported functions.
            Probably should be taken out of blead soon, and relevant prototypes
            changed.  */

       So doing this, and removing any of the unused variables
       still present would be good.

       Ordering of "global" variables.

       thrdvar.h and intrpvarh define the "global" variables that
       need to be per-thread under ithreads, where the variables
       are actually elements in a structure. As C dictates, the
       variables must be laid out in order of declaration. There
       is a comment "/* Important ones in the first cache line
       (if alignment is done right) */" which implies that at
       some point in the past the ordering was carefully chosen
       (at least in part). However, it's clear that the ordering
       is less than perfect, as currently there are things such
       as 7 "bool"s in a row, then something typically requiring
       4 byte alignment, and then an odd "bool" later on.
       ("bool"s are typically defined as "char"s). So it would be
       good for someone to review the ordering of the variables,
       to see how much alignment padding can be removed.

       bincompat functions

       There are lots of functions which are retained for binary
       compatibility.  Clean these up. Move them to mathom.c, and
       don't compile for blead?

       am I hot or not?

       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 anyone feeling like exercising their
       skill with coverage and profiling tools might want to
       determine what ops really are the most commonly used. And
       in turn suggest evictions and promotions to achieve a bet-
       ter pp_hot.c.

       emulate the per-thread memory pool on Unix

       For Windows, ithreads allocates memory for each thread
       from a separate pool, which it discards at thread exit. It
       also checks that memory is free()d to the correct pool.
       Neither check is done on Unix, so code developed there
       won't be subject to such strictures, so can harbour bugs



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       that only show up when the code reaches Windows.

       It would be good to be able to optionally emulate the Win-
       dow pool system on Unix, to let developers who only have
       access to Unix, or want to use Unix-specific debugging
       tools, check for these problems. To do this would involve
       figuring out how the "PerlMem_*" macros wrap "malloc()"
       access, and providing a layer that records/checks the
       identity of the thread making the call, and recording all
       the memory allocated by each thread via this API so that
       it can be summarily free()d at thread exit. One implemen-
       tation idea would be to increase the size of allocation,
       and store the "my_perl" pointer (to identify the thread)
       at the start, along with pointers to make a linked list of
       blocks for this thread. To avoid alignment problems it
       would be necessary to do something like

         union memory_header_padded {
           struct memory_header {
             void *thread_id;   /* For my_perl */
             void *next;        /* Pointer to next block for this thread */
           } data;
           long double padding; /* whatever type has maximal alignment constraint */
         };

       although "long double" might not be the only type to add
       to the padding union.

       reduce duplication in sv_setsv_flags

       "Perl_sv_setsv_flags" has a comment "/* There's a lot of
       redundancy below but we're going for speed here */"

       Whilst this was true 10 years ago, the growing disparity
       between RAM and CPU speeds mean that the trade offs have
       changed. In addition, the duplicate code adds to the main-
       tenance burden. It would be good to see how much of the
       redundancy can be pruned, particular in the less common
       paths. (Profiling tools at the ready...). For example, why
       does the test for "Can't redefine active sort subroutine"
       need to occur in two places?

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 mod-
       ules that use XS to interface to C.

       IPv6

       Clean this up. Check everything in core works







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       shrink "GV"s, "CV"s

       By removing unused elements and careful re-ordering, the
       structures for "AV"s and "HV"s have recently been shrunk
       considerably. It's probable that the same approach would
       find savings in "GV"s and "CV"s, if not all the other
       larger-than-"PVMG" types.

       merge Perl_sv_2[inpu]v

       There's a lot of code shared between "Perl_sv_2iv_flags",
       "Perl_sv_2uv_flags", "Perl_sv_2nv", and
       "Perl_sv_2pv_flags". It would be interesting to see if
       some of it can be merged into common shared static func-
       tions. In particular, "Perl_sv_2uv_flags" started out as a
       cut&paste from "Perl_sv_2iv_flags" around 5.005_50 time,
       and it may be possible to replace both with a single func-
       tion that returns a value or union which is split out by
       the macros in sv.h

       UTF8 caching code

       The string position/offset cache is not optional. It
       should be.

       Implicit Latin 1 => Unicode translation

       Conversions from byte strings to UTF-8 currently map high
       bit characters to Unicode without translation (or, depend-
       ing on how you look at it, by implicitly assuming that the
       byte strings are in Latin-1). As perl assumes the C locale
       by default, upgrading a string to UTF-8 may change the
       meaning of its contents regarding character classes, case
       mapping, etc.  This should probably emit a warning (at
       least).

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

       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



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       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.)

       Unicode in %ENV

       Currently the %ENV entries are always byte strings.

       use less 'memory'

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

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

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

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

       Make tainting consistent

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

       readpipe(LIST)

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

Tasks that need a knowledge of the interpreter
       These tasks would need C knowledge, and knowledge of how



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       the interpreter works, or a willingness to learn.

       lexical pragmas

       Document the new support for lexical pragmas in 5.9.3 and
       how %^H works.  Maybe "re", "encoding", maybe other prag-
       mas could be made lexical.

       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.

       Constant folding

       The peephole optimiser should trap errors during constant
       folding, and give up on the folding, rather than bailing
       out at compile time.  It is quite possible that the
       unfoldable constant is in unreachable code, eg something
       akin to "$a = 0/0 if 0;"

       LVALUE functions for lists

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

       LVALUE functions in the debugger

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

       _ prototype character

       Study the possibility of adding a new prototype character,
       "_", meaning "this argument defaults to $_".

       state variables

       "my $foo if 0;" is deprecated, and should be replaced with
       "state $x = "initial value\n";" the syntax from Perl 6.

       @INC source filter to Filter::Simple

       The second return value from a sub in @INC can be a source
       filter. This isn't documented. It should be changed to use
       Filter::Simple, tested and documented.







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       regexp optimiser optional

       The regexp optimiser is not optional. It should config-
       urable to be, to allow its performance to be measured, and
       its bugs to be easily demonstrated.

       UNITCHECK

       Introduce a new special block, UNITCHECK, which is run at
       the end of a compilation unit (module, file, eval(STRING)
       block). This will correspond to the Perl 6 CHECK. Perl 5's
       CHECK cannot be changed or removed because the O.pm/B.pm
       backend framework depends on it.

       optional optimizer

       Make the peephole optimizer optional. Currently it per-
       forms 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 optimisa-
       tions 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 mecha-
       nism 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 re- instated.

       Optimize away @_

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



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       What hooks would assertions need?

       Assertions are in the core, and work. However, assertions
       needed to be added as a core patch, rather than an XS mod-
       ule in ext, or a CPAN module, because the core has no
       hooks in the necessary places. It would be useful to
       investigate what hooks would need to be added to make it
       possible to provide the full assertion support from a CPAN
       module, so that we aren't constraining the imagination of
       future CPAN authors.

Big projects
       Tasks that will get your name mentioned in the description
       of the "Highlights of 5.10"

       make ithreads more robust

       Generally make ithreads more robust. See also "iCOW"

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

       iCOW

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

       (?{...}) closures in regexps

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

       A re-entrant regexp engine

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




















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