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Generalised "how many in list context" would be useful
[perl5.git] / pod / perltodo.pod
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1=head1 NAME
2
3perltodo - Perl TO-DO List
4
5=head1 DESCRIPTION
e50bb9a1 6
722d2a37 7This is a list of wishes for Perl. Send updates to
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8I<perl5-porters@perl.org>. If you want to work on any of these
9projects, be sure to check the perl5-porters archives for past ideas,
10flames, and propaganda. This will save you time and also prevent you
11from implementing something that Larry has already vetoed. One set
12of archives may be found at:
13
14 http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/
15
cd793d32 16=head1 assertions
e50bb9a1 17
cd793d32 18Clean up and finish support for assertions. See L<assertions>.
e50bb9a1 19
cd793d32 20=head1 iCOW
e50bb9a1 21
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22Sarathy and Arthur have a proposal for an improved Copy On Write which
23specifically will be able to COW new ithreads. If this can be implemented
24it would be a good thing.
e50bb9a1 25
cd793d32 26=head1 (?{...}) closures in regexps
4b3b956a 27
cd793d32 28Fix (or rewrite) the implementation of the C</(?{...})/> closures.
4b3b956a 29
cd793d32 30=head1 pragmata
e50bb9a1 31
cd793d32 32=head2 lexical pragmas
0562c0e3 33
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34Reimplement the mechanism of lexical pragmas to be more extensible. Fix
35current pragmas that don't work well (or at all) with lexical scopes or in
36run-time eval(STRING) (C<sort>, C<re>, C<encoding> for example). MJD has a
37preliminary patch that implements this.
0562c0e3 38
cd793d32 39=head2 use less 'memory'
f35392ae 40
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41Investigate trade offs to switch out perl's choices on memory usage.
42Particularly perl should be able to give memory back.
f35392ae 43
cd793d32 44=head1 prototypes and functions
c5fc23ff 45
cd793d32 46=head2 _ prototype character
e50bb9a1 47
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48Study the possibility of adding a new prototype character, C<_>, meaning
49"this argument defaults to $_".
e50bb9a1 50
cd793d32 51=head2 inlining autoloaded constants
776f8809 52
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53Currently the optimiser can inline constants when expressed as subroutines
54with prototype ($) that return a constant. Likewise, many packages wrapping
55C libraries export lots of constants as subroutines which are AUTOLOADed on
56demand. However, these have no prototypes, so can't be seen as constants by
57the optimiser. Some way of cheaply (low syntax, low memory overhead) to the
58perl compiler that a name is a constant would be great, so that it knows to
59call the AUTOLOAD routine at compile time, and then inline the constant.
776f8809 60
cd793d32 61=head2 Finish off lvalue functions
e50bb9a1 62
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63The old perltodo notes "They don't work in the debugger, and they don't work for
64list or hash slices."
e50bb9a1 65
cd793d32 66=head1 Unicode and UTF8
e50bb9a1 67
cd793d32 68=head2 Implicit Latin 1 => Unicode translation
e50bb9a1 69
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70Conversions from byte strings to UTF-8 currently map high bit characters
71to Unicode without translation (or, depending on how you look at it, by
72implicitly assuming that the byte strings are in Latin-1). As perl assumes
73the C locale by default, upgrading a string to UTF-8 may change the
74meaning of its contents regarding character classes, case mapping, etc.
75This should probably emit a warning (at least).
e50bb9a1 76
cd793d32 77=head2 UTF8 caching code
e50bb9a1 78
cd793d32 79The string position/offset cache is not optional. It should be.
e50bb9a1 80
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81=head2 Unicode in Filenames
82
83chdir, chmod, chown, chroot, exec, glob, link, lstat, mkdir, open,
84opendir, qx, readdir, readlink, rename, rmdir, stat, symlink, sysopen,
85system, truncate, unlink, utime, -X. All these could potentially accept
86Unicode filenames either as input or output (and in the case of system
87and qx Unicode in general, as input or output to/from the shell).
88Whether a filesystem - an operating system pair understands Unicode in
89filenames varies.
90
91Known combinations that have some level of understanding include
92Microsoft NTFS, Apple HFS+ (In Mac OS 9 and X) and Apple UFS (in Mac
93OS X), NFS v4 is rumored to be Unicode, and of course Plan 9. How to
94create Unicode filenames, what forms of Unicode are accepted and used
95(UCS-2, UTF-16, UTF-8), what (if any) is the normalization form used,
96and so on, varies. Finding the right level of interfacing to Perl
97requires some thought. Remember that an OS does not implicate a
98filesystem.
99
100(The Windows -C command flag "wide API support" has been at least
101temporarily retired in 5.8.1, and the -C has been repurposed, see
102L<perlrun>.)
103
104=head2 Unicode in %ENV
105
106Currently the %ENV entries are always byte strings.
107
cd793d32 108=head1 Regexps
e50bb9a1 109
cd793d32 110=head2 regexp optimiser optional
e50bb9a1 111
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112The regexp optimiser is not optional. It should configurable to be, to allow
113its performance to be measured, and its bugs to be easily demonstrated.
e50bb9a1 114
938c8732 115=head2 common suffices/prefices in regexps (trie optimization)
c47ff5f1 116
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117Currently, the user has to optimize C<foo|far> and C<foo|goo> into
118C<f(?:oo|ar)> and C<[fg]oo> by hand; this could be done automatically.
e50bb9a1 119
cd793d32 120=head1 POD
e50bb9a1 121
cd793d32 122=head2 POD -> HTML conversion still sucks
e50bb9a1 123
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124Which is crazy given just how simple POD purports to be, and how simple HTML
125can be.
126
cd793d32 127=head1 Misc medium sized projects
e50bb9a1 128
cd793d32 129=head2 UNITCHECK
e50bb9a1 130
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131Introduce a new special block, UNITCHECK, which is run at the end of a
132compilation unit (module, file, eval(STRING) block). This will correspond to
133the Perl 6 CHECK. Perl 5's CHECK cannot be changed or removed because the
134O.pm/B.pm backend framework depends on it.
e50bb9a1 135
cd793d32 136=head2 optional optimizer
e50bb9a1 137
cd793d32 138Make the peephole optimizer optional.
e50bb9a1 139
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140=head2 You WANT *how* many
141
142Currently contexts are void, scalar and list. sort has a special mechanism in
143place to pass in the number of return values wanted. It would be useful to
144have a general mechanism for this, backwards compatible and little speed hit.
145This would allow proposals such as short circuiting sort to be implemented
146as a module on CPAN.
147
cd793d32 148=head2 lexical aliases
e50bb9a1 149
cd793d32 150Allow lexical aliases (maybe via the syntax C<my \$alias = \$foo>.
e50bb9a1 151
cd793d32 152=head2 no 6
e50bb9a1 153
cd793d32 154Make C<no 6> and C<no v6> work (opposite of C<use 5.005>, etc.).
e50bb9a1 155
cd793d32 156=head2 IPv6
3958b146 157
cd793d32 158Clean this up. Check everything in core works
e50bb9a1 159
cd793d32 160=head2 entersub XS vs Perl
e50bb9a1 161
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162At the moment pp_entersub is huge, and has code to deal with entering both
163perl and and XS subroutines. Subroutine implementations rarely change between
164perl and XS at run time, so investigate using 2 ops to enter subs (one for
165XS, one for perl) and swap between if a sub is redefined.
e50bb9a1 166
cd793d32 167=head2 @INC source filter to Filter::Simple
e50bb9a1 168
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169The second return value from a sub in @INC can be a source filter. This isn't
170documented. It should be changed to use Filter::Simple, tested and documented.
e50bb9a1 171
cd793d32 172=head2 bincompat functions
e50bb9a1 173
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174There are lots of functions which are retained for binary compatibility.
175Clean these up. Move them to mathom.c, and don't compile for blead?
e50bb9a1 176
722d2a37 177=head2 Use fchown/fchmod internally
e50bb9a1 178
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179The old perltodo notes "This has been done in places, but needs a thorough
180code review. Also fchdir is available in some platforms."
e50bb9a1 181
cd793d32 182=head2 foreach reverse
e50bb9a1 183
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184The old perltodo notes that we could optimise foreach to iterate in reverse.
185(instead of making a reversed copy on the stack)
e50bb9a1 186
cd793d32 187=head1 Tests
e50bb9a1 188
cd793d32 189=head2 Make Schwern poorer
e50bb9a1 190
cd793d32 191Tests for everything, At which point Schwern coughs up $500 to TPF.
e50bb9a1 192
cd793d32 193=head2 test B
722d2a37 194
cd793d32 195A test suite for the B module would be nice.
722d2a37 196
cd793d32 197=head2 Improve tests for Config.pm
e50bb9a1 198
cd793d32 199Config.pm doesn't appear to be well tested.
e50bb9a1 200
cd793d32 201=head2 common test code for timed bailout
e50bb9a1 202
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203Write portable self destruct code for tests to stop them burning CPU in
204infinite loops. Needs to avoid using alarm, as some of the tests are testing
205alarm/sleep or timers.
e50bb9a1 206
cd793d32 207=head1 Installation
e50bb9a1 208
cd793d32 209=head2 compressed man pages
e50bb9a1 210
cd793d32 211Be able to install them
e50bb9a1 212
cd793d32 213=head2 Make Config.pm cope with differences between build and installed perl
e50bb9a1 214
cd793d32 215=head2 Relocatable perl
e50bb9a1 216
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217Make it possible to create a relocatable perl binary. Will need some collusion
218with Config.pm. We could use a syntax of ... for location of current binary?
e50bb9a1 219
cd793d32 220=head2 make HTML install work
e50bb9a1 221
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222=head2 put patchlevel in -v
223
224Currently perl from p4/rsync ships with a patchlevel.h file that usually
225defines one local patch, of the form "MAINT12345" or "RC1". The output of
226perl -v doesn't report that a perl isn't an official release, and this
227information can get lost in bugs reports. Because of this, the minor version
228isn't bumped up util RC time, to minimise the possibility of versions of perl
229escaping that believe themselves to be newer than they actually are.
230
231It would be useful to find an elegant way to have the "this is an interim
232maintenance release" or "this is a release candidate" in the terse -v output,
233and have it so that it's easy for the pumpking to remove this just as the
234release tarball is rolled up. This way the version pulled out of rsync would
235always say "I'm a development release" and it would be safe to bump the
236reported minor version as soon as a release ships, which would aid perl
237developers.
238
cd793d32 239=head1 Incremental things
e50bb9a1 240
cd793d32 241Some tasks that don't need to get done in one big hit.
e50bb9a1 242
cd793d32 243=head2 autovivification
e50bb9a1 244
cd793d32 245Make all autovivification consistent w.r.t LVALUE/RVALUE and strict/no strict;
e50bb9a1 246
cd793d32 247=head2 fix tainting bugs
e50bb9a1 248
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249Fix the bugs revealed by running the test suite with the C<-t> switch (via
250C<make test.taintwarn>).
e50bb9a1 251
cd793d32 252=head2 Make tainting consistent
e50bb9a1 253
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254Tainting would be easier to use if it didn't take documented shortcuts and allow
255taint to "leak" everywhere within an expression.
e50bb9a1 256
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257=head2 Dual life everything
258
259As part of the "dists" plan, anything that doesn't belong in the smallest perl
260distribution needs to be dual lifed. Anything else can be too.
261
cd793d32 262=head1 Vague things
e50bb9a1 263
cd793d32 264Some more nebulous ideas
e50bb9a1 265
cd793d32 266=head2 threads
e50bb9a1 267
cd793d32 268Make threads more robust.
e50bb9a1 269
cd793d32 270=head2 POSIX memory footprint
e50bb9a1 271
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272Ilya observed that use POSIX; eats memory like there's no tomorrow, and at
273various times worked to cut it down. There is probably still fat to cut out -
274for example POSIX passes Exporter some very memory hungry data structures.
e50bb9a1 275
cd793d32 276=head2 Optimize away @_
f86a8bc5 277
cd793d32 278The old perltodo notes "Look at the "reification" code in C<av.c>"
3298bd4d 279
cd793d32 280=head2 switch ops
3298bd4d 281
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282The old perltodo notes "Although we have C<Switch.pm> in core, Larry points to
283the dormant C<nswitch> and C<cswitch> ops in F<pp.c>; using these opcodes would
284be much faster."
0562c0e3 285
d10fc472 286=head2 Attach/detach debugger from running program
1626a787 287
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288The old perltodo notes "With C<gdb>, you can attach the debugger to a running
289program if you pass the process ID. It would be good to do this with the Perl
290debugger on a running Perl program, although I'm not sure how it would be done."
291ssh and screen do this with named pipes in tmp. Maybe we can too.
1626a787 292
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293=head2 A decent benchmark
294
295perlbench seems impervious to any recent changes made to the perl core. It would
296be useful to have a reasonable general benchmarking suite that roughly
297represented what current perl programs do, and measurably reported whether
298tweaks to the core improve, degrade or don't really affect performance, to
299guide people attempting to optimise the guts of perl.