3 re::engine::Plugin - API to write custom regex engines
7 This is a B<developer release> that requires a patch to blead to work,
8 the patch can be found in F<named_capture.patch> in this distribution.
12 As of perl 5.9.5 it's possible to lexically replace perl's built-in
13 regular expression engine with your own (see L<perlreapi> and
14 L<perlpragma>). This module provides a glue interface to the relevant
15 parts of the perl C API enabling you to write an engine in Perl
16 instead of the C/XS interface provided by the core.
18 =head2 The gory details
20 Each regex in perl is compiled into an internal C<REGEXP> structure
21 (see L<perlreapi|perlreapi/The REGEXP structure>), this can happen
22 either during compile time in the case of patterns in the format
23 C</pattern/> or runtime for C<qr//> patterns, or something inbetween
24 depending on variable interpolation etc.
26 When this module is loaded into a scope it inserts a hook into
27 C<$^H{regcomp}> (as described in L<perlreapi>) to have each regexp
28 constructed in its lexical scope handled by this engine, but it
29 differs from other engines in that it also inserts other hooks into
30 C<%^H> in the same scope that point to user-defined subroutines to use
31 during compilation, execution etc, these are described in
34 The callbacks (e.g. L</comp>) then get called with a
35 L<re::engine::Plugin> object as their first argument. This object
36 provies access to perl's internal REGEXP struct in addition to its own
37 state (e.g. a L<stash|/stash>). The L<methods|/METHODS> on this object
38 allow for altering the C<REGEXP> struct's internal state, adding new
43 Callbacks are specified in the C<re::engine::Plugin> import list as
44 key-value pairs of names and subroutine references:
46 use re::engine::Plugin (
51 To write a custom engine which imports your functions into the
52 caller's scope use use the following snippet:
54 package re::engine::Example;
55 use re::engine::Plugin ();
59 # Populates the caller's %^H with our callbacks
60 re::engine::Plugin->import(
66 *unimport = \&re::engine::Plugin::unimport;
68 # Implementation of the engine
79 # return value discarded
82 Called when a regex is compiled by perl, this is always the first
83 callback to be called and may be called multiple times or not at all
84 depending on what perl sees fit at the time.
86 The first argument will be a freshly constructed C<re::engine::Plugin>
87 object (think of it as C<$self>) which you can interact with using the
88 L<methods|/METHODS> below, this object will be passed around the other
89 L<callbacks|/CALLBACKS> and L<methods|/METHODS> for the lifetime of
92 Calling C<die> or anything that uses it (such as C<carp>) here will
93 not be trapped by an C<eval> block that the pattern is in, i.e.
96 use re::engine::Plugin(
99 croak "Your pattern is invalid"
100 unless $rx->pattern ~~ /pony/;
104 # Ignores the eval block
105 eval { /you die in C<eval>, you die for real/ };
107 This happens because the real subroutine call happens indirectly at
108 compile time and not in the scope of the C<eval> block. This is how
109 perl's own engine would behave in the same situation if given an
110 invalid pattern such as C</(/>.
117 # We always like ponies!
118 return 1 if $str ~~ /pony/;
124 Called when a regex is being executed, i.e. when it's being matched
125 against something. The scalar being matched against the pattern is
126 available as the second argument (C<$str>) and through the L<str|/str>
127 method. The routine should return a true value if the match was
128 successful, and a false one if it wasn't.
135 # in comp/exec/methods:
138 The last scalar to be matched against the L<pattern|/pattern> or
139 C<undef> if there hasn't been a match yet.
141 perl's own engine always stringifies the scalar being matched against
142 a given pattern, however a custom engine need not have such
143 restrictions. One could write a engine that matched a file handle
144 against a pattern or any other complex data structure.
148 The pattern that the engine was asked to compile, this can be either a
149 classic Perl pattern with modifiers like C</pat/ix> or C<qr/pat/ix> or
150 an arbitary scalar. The latter allows for passing anything that
151 doesn't fit in a string and five L<modifier|/mod> characters, such as
152 hashrefs, objects, etc.
157 say "has /ix" if %mod ~~ 'i' and %mod ~~ 'x';
159 A key-value pair list of the modifiers the pattern was compiled with.
160 The keys will zero or more of C<imsxp> and the values will be true
161 values (so that you don't have to write C<exists>).
163 You don't get to know if the C<eogc> modifiers were attached to the
164 pattern since these are internal to perl and shouldn't matter to
169 comp => sub { shift->stash( [ 1 .. 5 ) },
170 exec => sub { shift->stash }, # Get [ 1 .. 5 ]
172 Returns or sets a user defined stash that's passed around as part of
173 the C<$rx> object, useful for passing around all sorts of data between
174 the callback routines and methods.
179 my $minlen = $rx->minlen // "not set";
181 The minimum C<length> a string must be to match the pattern, perl will
182 use this internally during matching to check whether the stringified
183 form of the string (or other object) being matched is at least this
184 long, if not the regexp engine in effect (that means you!) will not be
187 The length specified will be used as a a byte length (using
188 L<SvPV|perlapi/SvPV>), not a character length.
194 my ($re, $paren) = @_;
199 my ($re, $paren, $rhs) = @_;
201 # return value discarded
204 my ($re, $paren) = @_;
210 Takes a list of key-value pairs of names and subroutines that
211 implement numbered capture variables. C<FETCH> will be called on value
212 retrieval (C<say $1>), C<STORE> on assignment (C<$1 = "ook">) and
213 C<LENGTH> on C<length $1>.
215 The second paramater of each routine is the paren number being
216 requested/stored, the following mapping applies for those numbers:
218 -2 => $` or ${^PREMATCH}
219 -1 => $' or ${^POSTMATCH}
224 Assignment to capture variables makes it possible to implement
225 something like Perl 6 C<:rw> semantics, and since it's possible to
226 make the capture variables return any scalar instead of just a string
227 it becomes possible to implement Perl 6 match object semantics (to
230 =head2 named_captures
234 This is implemented but not documented, see F<t/named_buff> for usage
239 The only way to untaint an existing variable in Perl is to use it as a
240 hash key or referencing subpatterns from a regular expression match
241 (see L<perlsec|perlsec/Laundering and Detecting Tainted Data>), the
242 latter only works in perl's regex engine because it explicitly
243 untaints capture variables which a custom engine will also need to do
244 if it wants its capture variables to be untanted.
246 There are basically two ways to go about this, the first and obvious
247 one is to make use of Perl'l lexical scoping which enables the use of
248 its built-in regex engine in the scope of the overriding engine's
251 use re::engine::Plugin (
253 my ($re, $str) = @_; # $str is tainted
257 my ($re, $paren) = @_;
259 # This is perl's engine doing the match
262 # $1 has been untainted
269 The second is to use something like L<Taint::Util> which flips the
270 taint flag on the scalar without invoking the perl's regex engine:
273 use re::engine::Plugin (
275 my ($re, $str) = @_; # $str is tainted
279 my ($re, $paren) = @_;
281 # Copy $str and untaint the copy
282 untaint(my $ret = $str);
284 # Return the untainted value
291 In either case a regex engine using perl's L<regex api|perlapi> or
292 this module is responsible for how and if it untaints its variables.
296 L<perlreapi>, L<Taint::Util>
298 =head1 TODO / CAVEATS
306 Export constants defined as macros in core relevant to our interests,
307 e.g. PMf_ stuff and things needed by extflags.
311 Engines implemented with this module don't support C<s///> and C<split
312 //>, the appropriate parts of the C<REGEXP> struct need to be wrapped
317 Still not a complete wrapper for L<perlreapi> in other ways, needs
318 methods for some C<REGEXP> struct members, some callbacks aren't
323 Support overloading operations on the C<qr//> object, this allow
324 control over the of C<qr//> objects in a manner that isn't limited by
325 C<wrapped>/C<wraplen>.
329 '@{}' => sub { ... },
335 Support the dispatch of arbitary methods from the re::engine::Plugin
336 qr// object to user defined subroutines via AUTOLOAD;
338 package re::engine::Plugin;
342 my ($name) = $AUTOLOAD =~ /.*::(.*?)/;
343 my $cv = getmeth($name); # or something like that
347 package re::engine::SomeEngine;
353 $re->add_method( # or something like that
355 my ($re, @arg) = @_; # re::engine::Plugin, 1..5
361 use re::engine::SomeEngine;
365 $re->foshizzle(1..5);
369 Implement the dupe callback, test this on a threaded perl (and learn
370 how to use threads and how they break the current model).
374 Allow the user to specify ->offs either as an array or a packed
375 string. Can pack() even pack I32? Only IV? int?
379 Add tests that check for different behavior when curpm is and is not
384 Add tests that check the refcount of the stash and other things I'm
385 mucking with, run valgrind and make sure everything is destroyed when
390 Run the debugger on the testsuite and find cases when the intuit and
391 checkstr callbacks are called. Write wrappers around them and add
398 Please report any bugs that aren't already listed at
399 L<http://rt.cpan.org/Dist/Display.html?Queue=re-engine-Plugin> to
400 L<http://rt.cpan.org/Public/Bug/Report.html?Queue=re-engine-Plugin>
404 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason <avar@cpan.org>
408 Copyright 2007 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason.
410 This program is free software; you can redistribute it and/or modify it
411 under the same terms as Perl itself.