3 perltodo - Perl TO-DO List
7 This is a list of wishes for Perl. Send updates to
8 I<perl5-porters@perl.org>. If you want to work on any of these
9 projects, be sure to check the perl5-porters archives for past ideas,
10 flames, and propaganda. This will save you time and also prevent you
11 from implementing something that Larry has already vetoed. One set
12 of archives may be found at:
14 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
18 Clean up and finish support for assertions. See L<assertions>.
22 Sarathy and Arthur have a proposal for an improved Copy On Write which
23 specifically will be able to COW new ithreads. If this can be implemented
24 it would be a good thing.
26 =head1 (?{...}) closures in regexps
28 Fix (or rewrite) the implementation of the C</(?{...})/> closures.
30 =head1 A re-entrant regexp engine
32 This will allow the use of a regex from inside (?{ }), (??{ }) and
33 (?(?{ })|) constructs.
37 =head2 lexical pragmas
39 Reimplement the mechanism of lexical pragmas to be more extensible. Fix
40 current pragmas that don't work well (or at all) with lexical scopes or in
41 run-time eval(STRING) (C<sort>, C<re>, C<encoding> for example). MJD has a
42 preliminary patch that implements this.
44 =head2 use less 'memory'
46 Investigate trade offs to switch out perl's choices on memory usage.
47 Particularly perl should be able to give memory back.
49 =head1 prototypes and functions
51 =head2 _ prototype character
53 Study the possibility of adding a new prototype character, C<_>, meaning
54 "this argument defaults to $_".
56 =head2 inlining autoloaded constants
58 Currently the optimiser can inline constants when expressed as subroutines
59 with prototype ($) that return a constant. Likewise, many packages wrapping
60 C libraries export lots of constants as subroutines which are AUTOLOADed on
61 demand. However, these have no prototypes, so can't be seen as constants by
62 the optimiser. Some way of cheaply (low syntax, low memory overhead) to the
63 perl compiler that a name is a constant would be great, so that it knows to
64 call the AUTOLOAD routine at compile time, and then inline the constant.
66 =head2 Finish off lvalue functions
68 The old perltodo notes "They don't work in the debugger, and they don't work for
71 =head1 Unicode and UTF8
73 =head2 Implicit Latin 1 => Unicode translation
75 Conversions from byte strings to UTF-8 currently map high bit characters
76 to Unicode without translation (or, depending on how you look at it, by
77 implicitly assuming that the byte strings are in Latin-1). As perl assumes
78 the C locale by default, upgrading a string to UTF-8 may change the
79 meaning of its contents regarding character classes, case mapping, etc.
80 This should probably emit a warning (at least).
82 =head2 UTF8 caching code
84 The string position/offset cache is not optional. It should be.
86 =head2 Unicode in Filenames
88 chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
89 opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
90 system, truncate, unlink, utime, -X. All these could potentially accept
91 Unicode filenames either as input or output (and in the case of system
92 and qx Unicode in general, as input or output to/from the shell).
93 Whether a filesystem - an operating system pair understands Unicode in
96 Known combinations that have some level of understanding include
97 Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
98 OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
99 create Unicode filenames, what forms of Unicode are accepted and used
100 (UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
101 and so on, varies. Finding the right level of interfacing to Perl
102 requires some thought. Remember that an OS does not implicate a
105 (The Windows -C command flag "wide API support" has been at least
106 temporarily retired in 5.8.1, and the -C has been repurposed, see
109 =head2 Unicode in %ENV
111 Currently the %ENV entries are always byte strings.
115 =head2 regexp optimiser optional
117 The regexp optimiser is not optional. It should configurable to be, to allow
118 its performance to be measured, and its bugs to be easily demonstrated.
122 =head2 POD -> HTML conversion still sucks
124 Which is crazy given just how simple POD purports to be, and how simple HTML
125 can be. It's not actually I<as> simple as it sounds, particularly with the
126 flexibility POD allows for C<=item>, but it would be good to improve the
127 visual appeal of the HTML generated, and to avoid it having any validation
128 errors. See also L</make HTML install work>, as the layout of installation tree
129 is needed to improve the cross-linking.
131 =head1 Misc medium sized projects
135 Introduce a new special block, UNITCHECK, which is run at the end of a
136 compilation unit (module, file, eval(STRING) block). This will correspond to
137 the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
138 O.pm/B.pm backend framework depends on it.
140 =head2 optional optimizer
142 Make the peephole optimizer optional.
144 =head2 You WANT *how* many
146 Currently contexts are void, scalar and list. split has a special mechanism in
147 place to pass in the number of return values wanted. It would be useful to
148 have a general mechanism for this, backwards compatible and little speed hit.
149 This would allow proposals such as short circuiting sort to be implemented
152 =head2 lexical aliases
154 Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
158 Make C<no 6> and C<no v6> work (opposite of C<use 5.005>, etc.).
162 Clean this up. Check everything in core works
164 =head2 entersub XS vs Perl
166 At the moment pp_entersub is huge, and has code to deal with entering both
167 perl and XS subroutines. Subroutine implementations rarely change between
168 perl and XS at run time, so investigate using 2 ops to enter subs (one for
169 XS, one for perl) and swap between if a sub is redefined.
171 =head2 @INC source filter to Filter::Simple
173 The second return value from a sub in @INC can be a source filter. This isn't
174 documented. It should be changed to use Filter::Simple, tested and documented.
176 =head2 bincompat functions
178 There are lots of functions which are retained for binary compatibility.
179 Clean these up. Move them to mathom.c, and don't compile for blead?
181 =head2 Constant folding
183 The peephole optimiser should trap errors during constant folding, and give
184 up on the folding, rather than bailing out at compile time. It is quite
185 possible that the unfoldable constant is in unreachable code, eg something
186 akin to C<$a = 0/0 if 0;>
190 =head2 Make Schwern poorer
192 Tests for everything, At which point Schwern coughs up $500 to TPF.
196 A test suite for the B module would be nice.
198 =head2 common test code for timed bailout
200 Write portable self destruct code for tests to stop them burning CPU in
201 infinite loops. Needs to avoid using alarm, as some of the tests are testing
202 alarm/sleep or timers.
206 =head2 compressed man pages
208 Be able to install them. This would probably need a configure test to see how
209 the system does compressed man pages (same directory/different directory?
210 same filename/different filename), as well as tweaking the F<installman> script
211 to compress as necessary.
213 =head2 Make Config.pm cope with differences between build and installed perl
215 Quite often vendors ship a perl binary compiled with their (pay-for)
216 compilers. People install a free compiler, such as gcc. To work out how to
217 build extensions, Perl interrogates C<%Config>, so in this situation
218 C<%Config> describes compilers that aren't there, and extension building
219 fails. This forces people into chosing between re-compiling perl themselves
220 using the compiler they have, or only using modules that the vendor ships.
222 It would be good to find a way teach C<Config.pm> about the installation setup,
223 possibly involving probing at install time or later, so that the C<%Config> in
224 a binary distruction better describes the installed machine, when the installed
225 machine differs from the build machine in some significant way.
227 =head2 Relocatable perl
229 Make it possible to create a relocatable perl binary. Will need some collusion
230 with Config.pm. We could use a syntax of ... for location of current binary?
232 =head2 make HTML install work
234 There is an C<installhtml> target in the Makefile. It's marked as
235 "experimental". It would be good to get this tested, make it work reliably, and
236 remove the "experimental" tag. This would include
242 Checking that cross linking between various parts of the documentation works.
243 In particular that links work between the modules (files with POD in F<lib/>)
244 and the core documentation (files in F<pod/>)
248 Work out how to split perlfunc into chunks, preferably one per function group,
249 preferably with general case code that could be used elsewhere. Challenges
250 here are correctly identifying the groups of functions that go together, and
251 making the right named external cross-links point to the right page. Things to
252 be aware of are C<-X>, groups such as C<getpwnam> to C<endservent>, two or
253 more C<=items> giving the different parameter lists, such as
255 =item substr EXPR,OFFSET,LENGTH,REPLACEMENT
257 =item substr EXPR,OFFSET,LENGTH
259 =item substr EXPR,OFFSET
261 and different parameter lists having different meanings. (eg C<select>)
265 =head2 put patchlevel in -v
267 Currently perl from p4/rsync ships with a patchlevel.h file that usually
268 defines one local patch, of the form "MAINT12345" or "RC1". The output of
269 perl -v doesn't report that a perl isn't an official release, and this
270 information can get lost in bugs reports. Because of this, the minor version
271 isn't bumped up until RC time, to minimise the possibility of versions of perl
272 escaping that believe themselves to be newer than they actually are.
274 It would be useful to find an elegant way to have the "this is an interim
275 maintenance release" or "this is a release candidate" in the terse -v output,
276 and have it so that it's easy for the pumpking to remove this just as the
277 release tarball is rolled up. This way the version pulled out of rsync would
278 always say "I'm a development release" and it would be safe to bump the
279 reported minor version as soon as a release ships, which would aid perl
282 =head1 Incremental things
284 Some tasks that don't need to get done in one big hit.
286 =head2 autovivification
288 Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
290 =head2 fix tainting bugs
292 Fix the bugs revealed by running the test suite with the C<-t> switch (via
293 C<make test.taintwarn>).
295 =head2 Make tainting consistent
297 Tainting would be easier to use if it didn't take documented shortcuts and allow
298 taint to "leak" everywhere within an expression.
300 =head2 Dual life everything
302 As part of the "dists" plan, anything that doesn't belong in the smallest perl
303 distribution needs to be dual lifed. Anything else can be too.
307 Some more nebulous ideas
315 Re-implement C<:unique> in a way that is actually thread-safe
319 Make C<threads::shared> share aggregates properly
321 (these two may actually share approach, if not implementation
325 Generally make threads more robust. See also L<iCOW>
327 =head2 POSIX memory footprint
329 Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
330 various times worked to cut it down. There is probably still fat to cut out -
331 for example POSIX passes Exporter some very memory hungry data structures.
333 =head2 Optimize away @_
335 The old perltodo notes "Look at the "reification" code in C<av.c>".
339 The old perltodo notes "Although we have C<Switch.pm> in core, Larry points to
340 the dormant C<nswitch> and C<cswitch> ops in F<pp.c>; using these opcodes would
343 =head2 Attach/detach debugger from running program
345 The old perltodo notes "With C<gdb>, you can attach the debugger to a running
346 program if you pass the process ID. It would be good to do this with the Perl
347 debugger on a running Perl program, although I'm not sure how it would be done."
348 ssh and screen do this with named pipes in tmp. Maybe we can too.
350 =head2 A decent benchmark
352 perlbench seems impervious to any recent changes made to the perl core. It would
353 be useful to have a reasonable general benchmarking suite that roughly
354 represented what current perl programs do, and measurably reported whether
355 tweaks to the core improve, degrade or don't really affect performance, to
356 guide people attempting to optimise the guts of perl.
358 =head2 readpipe(LIST)
360 system() accepts a LIST syntax (and a PROGRAM LIST syntax) to avoid
361 running a shell. readpipe() (the function behind qx//) could be similarly
366 self ties are currently illegal because they caused too many segfaults. Maybe
367 the causes of these could be tracked down and self-ties on all types re-