X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperltodo.pod;h=a8a6d797cc656c8d6a8f5f1ea164dd8c8c487de4;hb=3246d7a3ad86dfa806dd7e514ae5fd2dacd5c0ef;hp=28a9e31cd489b50281edd3848ae8b52e715dd59f;hpb=d7f8936a2fe7fc93635b0b501d1f941d30d3399f;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/pod/perltodo.pod b/pod/perltodo.pod
index 28a9e31..a8a6d79 100644
--- a/pod/perltodo.pod
+++ b/pod/perltodo.pod
@@ -4,204 +4,202 @@ perltodo - Perl TO-DO List
 
 =head1 DESCRIPTION
 
-This is a list of wishes for Perl.  Send updates to
-I<perl5-porters@perl.org>.  If you want to work on any of these
-projects, be sure to check the perl5-porters archives for past ideas,
-flames, and propaganda.  This will save you time and also prevent you
-from implementing something that Larry has already vetoed.  One set
-of archives may be found at:
+This is a list of wishes for Perl. The tasks we think are smaller or easier
+are listed first. Anyone is welcome to work on any of these, but it's a good
+idea to first contact I<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/
 
-=head1 assertions
+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
+F<AUTHORS> file, which ships in the official distribution. How many other
+programming languages offer you 1 line of immortality?
 
-Clean up and finish support for assertions. See L<assertions>.
+=head1 The roadmap to 5.10
 
-=head1 iCOW
+The roadmap to 5.10 envisages feature based releases, as various items in this
+TODO are completed.
 
-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.
+=head2 Needed for a 5.9.4 release
 
-=head1 (?{...}) closures in regexps
+=over
 
-Fix (or rewrite) the implementation of the C</(?{...})/> closures.
+=item *
 
-=head1 A re-entrant regexp engine
+Review assertions. Review syntax to combine assertions. Assertions could take
+advantage of the lexical pragmas work. L</What hooks would assertions need?>
 
-This will allow the use of a regex from inside (?{ }), (??{ }) and
-(?(?{ })|) constructs.
+=back
 
-=head1 pragmata
+=head2 Needed for a 5.9.5 release
 
-=head2 lexical pragmas
+=over
 
-Reimplement the mechanism of lexical pragmas to be more extensible. Fix
-current pragmas that don't work well (or at all) with lexical scopes or in
-run-time eval(STRING) (C<sort>, C<re>, C<encoding> for example). MJD has a
-preliminary patch that implements this.
+=item *
+Implement L</_ prototype character>
 
-=head2 use less 'memory'
+=item *
+Implement L</state variables>
 
-Investigate trade offs to switch out perl's choices on memory usage.
-Particularly perl should be able to give memory back.
+=back
 
-=head1 prototypes and functions
+=head2 Needed for a 5.9.6 release
 
-=head2 _ prototype character
+Stabilisation. If all goes well, this will be the equivalent of a 5.10-beta.
 
-Study the possibility of adding a new prototype character, C<_>, meaning
-"this argument defaults to $_".
+=head1 Tasks that only need Perl knowledge
 
-=head2 inlining autoloaded constants
+=head2 common test code for timed bail out
 
-Currently the optimiser can inline constants when expressed as subroutines
-with prototype ($) that return a constant. Likewise, many packages wrapping
-C libraries export lots of constants as subroutines which are AUTOLOADed on
-demand. However, these have no prototypes, so can't be seen as constants by
-the optimiser. Some way of cheaply (low syntax, low memory overhead) to the
-perl compiler that a name is a constant would be great, so that it knows to
-call the AUTOLOAD routine at compile time, and then inline the constant.
+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.
 
-=head2 Finish off lvalue functions
+=head2 POD -> HTML conversion in the core still sucks
 
-The old perltodo notes "They don't work in the debugger, and they don't work for
-list or hash slices."
+Which is crazy given just how simple POD purports to be, and how simple HTML
+can be. It's not actually I<as> simple as it sounds, particularly with the
+flexibility POD allows for C<=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 L</make HTML install work>, as the layout of installation tree
+is needed to improve the cross-linking.
 
-=head1 Unicode and UTF8
+The addition of C<Pod::Simple> and its related modules may make this task
+easier to complete.
 
-=head2 Implicit Latin 1 => Unicode translation
+=head2 Parallel testing
 
-Conversions from byte strings to UTF-8 currently map high bit characters
-to Unicode without translation (or, depending 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).
+The core regression test suite is getting ever more comprehensive, 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 B<option> of
+running sets of tests in parallel. This would be useful for tests in
+F<t/op/*.t> and F<t/uni/*.t> and maybe some sets of tests in F<lib/>.
 
-=head2 UTF8 caching code
+Questions to answer
 
-The string position/offset cache is not optional. It should be.
+=over 4
 
-=head2 Unicode in Filenames
+=item 1
 
-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.
+How does screen layout work when you're running more than one test?
 
-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.
+=item 2
 
-(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
-L<perlrun>.)
+How does the caller of test specify how many tests to run in parallel?
 
-=head2 Unicode in %ENV
+=item 3
 
-Currently the %ENV entries are always byte strings.
+How do setup/teardown tests identify themselves?
 
-=head1 Regexps
+=back
 
-=head2 regexp optimiser optional
+Pugs already does parallel testing - can their approach be re-used?
 
-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.
+=head2 Make Schwern poorer
 
-=head1 POD
+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.
 
-=head2 POD -> HTML conversion still sucks
+See F<t/lib/1_compile.t> for the 3 remaining modules that need tests.
 
-Which is crazy given just how simple POD purports to be, and how simple HTML
-can be. It's not actually I<as> simple as it sounds, particularly with the
-flexibility POD allows for C<=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 L</make HTML install work>, as the layout of installation tree
-is needed to improve the cross-linking.
+=head2 Improve the coverage of the core tests
 
-=head1 Misc medium sized projects
+Use Devel::Cover to ascertain the core's test coverage, then add tests that
+are currently missing.
 
-=head2 UNITCHECK
+=head2 test B
 
-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.
+A full test suite for the B module would be nice.
 
-=head2 optional optimizer
+=head2 A decent benchmark
 
-Make the peephole optimizer optional.
+C<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.
 
-=head2 You WANT *how* many
+=head2 fix tainting bugs
 
-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.
+Fix the bugs revealed by running the test suite with the C<-t> switch (via
+C<make test.taintwarn>).
 
-=head2 lexical aliases
+=head2 Dual life everything
 
-Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
+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.
 
-=head2 no 6
+=head2 Improving C<threads::shared>
 
-Make C<no 6> and C<no v6> work (opposite of C<use 5.005>, etc.).
+Investigate whether C<threads::shared> could share aggregates properly with
+only Perl level changes to shared.pm
 
-=head2 IPv6
+=head2 POSIX memory footprint
 
-Clean this up. Check everything in core works
+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.
 
-=head2 entersub XS vs Perl
 
-At the moment pp_entersub is huge, and has code to deal with entering both
-perl and 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.
 
-=head2 @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.
 
-=head2 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?
 
-=head2 Constant folding
+=head1 Tasks that need a little sysadmin-type knowledge
 
-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 C<$a = 0/0 if 0;>
+Or if you prefer, tasks that you would learn from, and broaden your skills
+base...
 
-=head1 Tests
+=head2 Relocatable perl
 
-=head2 Make Schwern poorer
+The C level patches needed to create a relocatable perl binary are done, as
+is the work on F<Config.pm>. All that's left to do is the C<Configure> tweaking
+to let people specify how they want to do the install.
 
-Tests for everything, At which point Schwern coughs up $500 to TPF.
+=head2 make HTML install work
 
-=head2 test B
+There is an C<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
 
-A test suite for the B module would be nice.
+=over 4
 
-=head2 common test code for timed bailout
+=item 1
 
-Write portable self destruct code for tests to stop them burning CPU in
-infinite loops. Needs to avoid using alarm, as some of the tests are testing
-alarm/sleep or timers.
+Checking that cross linking between various parts of the documentation works.
+In particular that links work between the modules (files with POD in F<lib/>)
+and the core documentation (files in F<pod/>)
+
+=item 2
+
+Work out how to split C<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 C<-X>, groups such as C<getpwnam> to
+C<endservent>, two or more C<=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 C<select>)
 
-=head1 Installation
+=back
 
 =head2 compressed man pages
 
@@ -210,63 +208,115 @@ the system does compressed man pages (same directory/different directory?
 same filename/different filename), as well as tweaking the F<installman> script
 to compress as necessary.
 
+=head2 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
+
+=over 4
+
+=item *
+
+do a normal C<Configure>, but include Devel::Cover as a module to install
+(see F<INSTALL> for how to do this)
+
+=item *
+
+    make perl
+
+=item *
+
+    cd t; HARNESS_PERL_SWITCHES=-MDevel::Cover ./perl -I../lib harness
+
+=item *
+
+Process the resulting Devel::Cover database
+
+=back
+
+This just give you the coverage of the F<.pm>s. To also get the C level
+coverage you need to
+
+=over 4
+
+=item *
+
+Additionally tell C<Configure> to use the appropriate C compiler flags for
+C<gcov>
+
+=item *
+
+    make perl.gcov
+
+(instead of C<make perl>)
+
+=item *
+
+After running the tests run C<gcov> to generate all the F<.gcov> files.
+(Including down in the subdirectories of F<ext/>
+
+=item *
+
+(From the top level perl directory) run C<gcov2perl> on all the C<.gcov> files
+to get their stats into the cover_db directory.
+
+=item *
+
+Then process the Devel::Cover database
+
+=back
+
+It would be good to add a single switch to C<Configure> to specify that you
+wanted to perform perl level coverage, and another to specify C level
+coverage, and have C<Configure> and the F<Makefile> do all the right things
+automatically.
+
 =head2 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 interrogates C<%Config>, so in this situation
 C<%Config> describes compilers that aren't there, and extension building
-fails. This forces people into chosing between re-compiling perl themselves
+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 C<Config.pm> about the installation setup,
 possibly involving probing at install time or later, so that the C<%Config> in
-a binary distruction better describes the installed machine, when the installed
-machine differs from the build machine in some significant way.
+a binary distribution better describes the installed machine, when the
+installed machine differs from the build machine in some significant way.
 
-=head2 Relocatable perl
+=head2 make parallel builds work
 
-Make it possible to create a relocatable perl binary. Will need some collusion
-with Config.pm. We could use a syntax of ... for location of current binary?
+Currently parallel builds (such as C<make -j3>) don't work reliably. We believe
+that this is due to incomplete dependency specification in the F<Makefile>.
+It would be good if someone were able to track down the causes of these
+problems, so that parallel builds worked properly.
 
-=head2 make HTML install work
-
-There is an C<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
+=head2 linker specification files
 
-=over 4
-
-=item 1
-
-Checking that cross linking between various parts of the documentation works.
-In particular that links work between the modules (files with POD in F<lib/>)
-and the core documentation (files in F<pod/>)
+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
+F<makedef.pl> to support this format, and to provide a means within
+C<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.
 
-=item 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 C<-X>, groups such as C<getpwnam> to C<endservent>, two or
-more C<=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 C<select>)
+=head1 Tasks that need a little C knowledge
 
-=back
+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
 
-=head2 put patchlevel in -v
+=head2 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
+Currently perl from C<p4>/C<rsync> ships with a F<patchlevel.h> file that
+usually defines one local patch, of the form "MAINT12345" or "RC1". The output
+of perl -v doesn't report that a perl isn't an official release, and this
 information can get lost in bugs reports. Because of this, the minor version
 isn't bumped up until RC time, to minimise the possibility of versions of perl
 escaping that believe themselves to be newer than they actually are.
@@ -279,90 +329,339 @@ 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.
 
-=head1 Incremental things
+This task is really about thinking of an elegant way to arrange the C source
+such that it's trivial for the Pumpking to flag "this is an official release"
+when making a tarball, yet leave the default source saying "I'm not the
+official release".
+
+=head2 Tidy up global variables
+
+There's a note in F<intrpvar.h>
+
+  /* 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.
+
+=head2 Ordering of "global" variables.
+
+F<thrdvar.h> and F<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
+C</* 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 C<bool>s in a row, then something
+typically requiring 4 byte alignment, and then an odd C<bool> later on.
+(C<bool>s are typically defined as C<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.
+
+=head2 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?
+
+=head2 am I hot or not?
+
+The idea of F<pp_hot.c> is that it contains the I<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 I<really> are the most commonly used. And in
+turn suggest evictions and promotions to achieve a better F<pp_hot.c>.
+
+=head2 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 that only show up when the
+code reaches Windows.
+
+It would be good to be able to optionally emulate the Window 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 C<PerlMem_*> macros wrap C<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 implementation idea
+would be to increase the size of allocation, and store the C<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 C<long double> might not be the only type to add to the padding
+union.
+
+=head2 reduce duplication in sv_setsv_flags
+
+C<Perl_sv_setsv_flags> has a comment
+C</* 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 maintenance 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?
+
+
+
+
+=head1 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.
+
+=head2 IPv6
+
+Clean this up. Check everything in core works
+
+=head2 shrink C<GV>s, C<CV>s
+
+By removing unused elements and careful re-ordering, the structures for C<AV>s
+and C<HV>s have recently been shrunk considerably. It's probable that the same
+approach would find savings in C<GV>s and C<CV>s, if not all the other
+larger-than-C<PVMG> types.
+
+=head2 merge Perl_sv_2[inpu]v
+
+There's a lot of code shared between C<Perl_sv_2iv_flags>,
+C<Perl_sv_2uv_flags>, C<Perl_sv_2nv>, and C<Perl_sv_2pv_flags>. It would be
+interesting to see if some of it can be merged into common shared static
+functions. In particular, C<Perl_sv_2uv_flags> started out as a cut&paste
+from C<Perl_sv_2iv_flags> around 5.005_50 time, and it may be possible to
+replace both with a single function that returns a value or union which is
+split out by the macros in F<sv.h>
+
+=head2 UTF8 caching code
+
+The string position/offset cache is not optional. It should be.
+
+=head2 Implicit Latin 1 => Unicode translation
+
+Conversions from byte strings to UTF-8 currently map high bit characters
+to Unicode without translation (or, depending 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).
 
-Some tasks that don't need to get done in one big hit.
+This task is incremental - even a little bit of work on it will help.
 
 =head2 autovivification
 
 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
 
-=head2 fix tainting bugs
+This task is incremental - even a little bit of work on it will help.
 
-Fix the bugs revealed by running the test suite with the C<-t> switch (via
-C<make test.taintwarn>).
+=head2 Unicode in Filenames
 
-=head2 Make tainting consistent
+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.
 
-Tainting would be easier to use if it didn't take documented shortcuts and allow
-taint to "leak" everywhere within an expression.
+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.
 
-=head2 Dual life everything
+(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
+L<perlrun>.)
 
-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.
+=head2 Unicode in %ENV
 
-=head1 Vague things
+Currently the %ENV entries are always byte strings.
 
-Some more nebulous ideas
+=head2 use less 'memory'
 
-=head2 threads
+Investigate trade offs to switch out perl's choices on memory usage.
+Particularly perl should be able to give memory back.
 
-=over 4
+This task is incremental - even a little bit of work on it will help.
 
-=item *
+=head2 Re-implement C<:unique> in a way that is actually thread-safe
 
-Re-implement C<: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 C<: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 F<Config>.
 
-=item *
+=head2 Make tainting consistent
 
-Make C<threads::shared> share aggregates properly
+Tainting would be easier to use if it didn't take documented shortcuts and
+allow taint to "leak" everywhere within an expression.
 
-(these two may actually share approach, if not implementation
+=head2 readpipe(LIST)
 
-=back
+system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
+running a shell. readpipe() (the function behind qx//) could be similarly
+extended.
 
-Generally make threads more robust. See also L<iCOW>
 
-=head2 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.
 
-=head2 Optimize away @_
 
-The old perltodo notes "Look at the "reification" code in C<av.c>".
+=head1 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.
 
-=head2 switch ops
+=head2 lexical pragmas
 
-The old perltodo notes "Although we have C<Switch.pm> in core, Larry points to
-the dormant C<nswitch> and C<cswitch> ops in F<pp.c>; using these opcodes would
-be much faster."
+Document the new support for lexical pragmas in 5.9.3 and how %^H works.
+Maybe C<re>, C<encoding>, maybe other pragmas could be made lexical.
 
 =head2 Attach/detach debugger from running program
 
 The old perltodo notes "With C<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.
+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.
 
-=head2 A decent benchmark
+=head2 Constant folding
 
-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.
+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 C<$a = 0/0 if 0;>
 
-=head2 readpipe(LIST)
+=head2 LVALUE functions for lists
 
-system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
-running a shell. readpipe() (the function behind qx//) could be similarly
-extended.
+The old perltodo notes that lvalue functions don't work for list or hash
+slices. This would be good to fix.
+
+=head2 LVALUE functions in the debugger
+
+The old perltodo notes that lvalue functions don't work in the debugger. This
+would be good to fix.
+
+=head2 _ prototype character
+
+Study the possibility of adding a new prototype character, C<_>, meaning
+"this argument defaults to $_".
+
+=head2 state variables
+
+C<my $foo if 0;> is deprecated, and should be replaced with
+C<state $x = "initial value\n";> the syntax from Perl 6.
+
+=head2 @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.
+
+=head2 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.
+
+=head2 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.
+
+=head2 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.
+
+=head2 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.
+
+=head2 lexical aliases
+
+Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
+
+=head2 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.
 
 =head2 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.
+
+=head2 Optimize away @_
+
+The old perltodo notes "Look at the "reification" code in C<av.c>".
+
+=head2 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 module 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.
+
+
+
+
+
+=head1 Big projects
+
+Tasks that will get your name mentioned in the description of the "Highlights
+of 5.10"
+
+=head2 make ithreads more robust
+
+Generally make ithreads more robust. See also L</iCOW>
+
+This task is incremental - even a little bit of work on it will help, and
+will be greatly appreciated.
+
+=head2 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.
+
+=head2 (?{...}) closures in regexps
+
+Fix (or rewrite) the implementation of the C</(?{...})/> closures.
+
+=head2 A re-entrant regexp engine
+
+This will allow the use of a regex from inside (?{ }), (??{ }) and
+(?(?{ })|) constructs.