2 re::engine::Plugin - API to write custom regex engines
8 As of perl 5.9.5 it's possible to lexically replace perl's built-in
9 regular expression engine with your own (see perlreapi and perlpragma).
10 This module provides a glue interface to the relevant parts of the perl
11 C API enabling you to write an engine in Perl instead of the C/XS
12 interface provided by the core.
15 Each regex in perl is compiled into an internal "REGEXP" structure (see
16 perlreapi), this can happen either during compile time in the case of
17 patterns in the format "/pattern/" or runtime for "qr//" patterns, or
18 something inbetween depending on variable interpolation etc.
20 When this module is loaded into a scope it inserts a hook into
21 $^H{regcomp} (as described in perlreapi and perlpragma) to have each
22 regexp constructed in its lexical scope handled by this engine, but it
23 differs from other engines in that it also inserts other hooks into
24 "%^H" in the same scope that point to user-defined subroutines to use
25 during compilation, execution etc, these are described in "CALLBACKS"
28 The callbacks (e.g. "comp") then get called with a re::engine::Plugin
29 object as their first argument. This object provies access to perl's
30 internal REGEXP struct in addition to its own state (e.g. a stash). The
31 methods on this object allow for altering the "REGEXP" struct's internal
32 state, adding new callbacks, etc.
35 Callbacks are specified in the "re::engine::Plugin" import list as
36 key-value pairs of names and subroutine references:
38 use re::engine::Plugin (
43 To write a custom engine which imports your functions into the caller's
44 scope use use the following snippet:
46 package re::engine::Example;
47 use re::engine::Plugin ();
51 # Sets the caller's $^H{regcomp} his %^H with our callbacks
52 re::engine::Plugin->import(
58 *unimport = \&re::engine::Plugin::unimport;
60 # Implementation of the engine
70 # return value discarded
73 Called when a regex is compiled by perl, this is always the first
74 callback to be called and may be called multiple times or not at all
75 depending on what perl sees fit at the time.
77 The first argument will be a freshly constructed "re::engine::Plugin"
78 object (think of it as $self) which you can interact with using the
79 methods below, this object will be passed around the other callbacks and
80 methods for the lifetime of the regex.
82 Calling "die" or anything that uses it (such as "carp") here will not be
83 trapped by an "eval" block that the pattern is in, i.e.
86 use re::engine::Plugin(
89 croak "Your pattern is invalid"
90 unless $rx->pattern ~~ /pony/;
94 # Ignores the eval block
95 eval { /you die in C<eval>, you die for real/ };
97 This happens because the real subroutine call happens indirectly at
98 compile time and not in the scope of the "eval" block. This is how
99 perl's own engine would behave in the same situation if given an invalid
100 pattern such as "/(/".
106 # We always like ponies!
107 return 1 if $str ~~ /pony/;
113 Called when a regex is being executed, i.e. when it's being matched
114 against something. The scalar being matched against the pattern is
115 available as the second argument ($str) and through the str method. The
116 routine should return a true value if the match was successful, and a
117 false one if it wasn't.
119 This callback can also be specified on an individual basis with the
125 # in comp/exec/methods:
128 The last scalar to be matched against the pattern or "undef" if there
129 hasn't been a match yet.
131 perl's own engine always stringifies the scalar being matched against a
132 given pattern, however a custom engine need not have such restrictions.
133 One could write a engine that matched a file handle against a pattern or
134 any other complex data structure.
137 The pattern that the engine was asked to compile, this can be either a
138 classic Perl pattern with modifiers like "/pat/ix" or "qr/pat/ix" or an
139 arbitary scalar. The latter allows for passing anything that doesn't fit
140 in a string and five modifier characters, such as hashrefs, objects,
145 say "has /ix" if %mod ~~ 'i' and %mod ~~ 'x';
147 A key-value pair list of the modifiers the pattern was compiled with.
148 The keys will zero or more of "imsxp" and the values will be true values
149 (so that you don't have to write "exists").
151 You don't get to know if the "eogc" modifiers were attached to the
152 pattern since these are internal to perl and shouldn't matter to regexp
156 comp => sub { shift->stash( [ 1 .. 5 ) },
157 exec => sub { shift->stash }, # Get [ 1 .. 5 ]
159 Returns or sets a user defined stash that's passed around as part of the
160 $rx object, useful for passing around all sorts of data between the
161 callback routines and methods.
165 my $minlen = $rx->minlen // "not set";
167 The minimum "length" a string must be to match the pattern, perl will
168 use this internally during matching to check whether the stringified
169 form of the string (or other object) being matched is at least this
170 long, if not the regexp engine in effect (that means you!) will not be
173 The length specified will be used as a a byte length (using SvPV), not a
179 # A dumb regexp engine that just tests string equality
180 use re::engine::Plugin comp => sub {
183 my $pat = $re->pattern;
193 Takes a list of key-value pairs of names and subroutines, and replace
194 the callback currently attached to the regular expression for the type
195 given as the key by the code reference passed as the corresponding
198 The only valid key is currently "exec". See "exec" for more details
204 my ($re, $paren) = @_;
209 my ($re, $paren, $rhs) = @_;
211 # return value discarded
214 my ($re, $paren) = @_;
220 Takes a list of key-value pairs of names and subroutines that implement
221 numbered capture variables. "FETCH" will be called on value retrieval
222 ("say $1"), "STORE" on assignment ("$1 = "ook"") and "LENGTH" on "length
225 The second paramater of each routine is the paren number being
226 requested/stored, the following mapping applies for those numbers:
228 -2 => $` or ${^PREMATCH}
229 -1 => $' or ${^POSTMATCH}
234 Assignment to capture variables makes it possible to implement something
235 like Perl 6 ":rw" semantics, and since it's possible to make the capture
236 variables return any scalar instead of just a string it becomes possible
237 to implement Perl 6 match object semantics (to name an example).
242 perl internals still needs to be changed to support this but when it's
243 done it'll allow the binding of "%+" and "%-" and support the Tie::Hash
244 methods FETCH, STORE, DELETE, CLEAR, EXISTS, FIRSTKEY, NEXTKEY and
249 True iff the module could have been built with thread-safety features
253 True iff this module could have been built with fork-safety features
254 enabled. This will always be true except on Windows where it's false for
255 perl 5.10.0 and below.
258 The only way to untaint an existing variable in Perl is to use it as a
259 hash key or referencing subpatterns from a regular expression match (see
260 perlsec), the latter only works in perl's regex engine because it
261 explicitly untaints capture variables which a custom engine will also
262 need to do if it wants its capture variables to be untanted.
264 There are basically two ways to go about this, the first and obvious one
265 is to make use of Perl'l lexical scoping which enables the use of its
266 built-in regex engine in the scope of the overriding engine's callbacks:
268 use re::engine::Plugin (
270 my ($re, $str) = @_; # $str is tainted
274 my ($re, $paren) = @_;
276 # This is perl's engine doing the match
279 # $1 has been untainted
286 The second is to use something like Taint::Util which flips the taint
287 flag on the scalar without invoking the perl's regex engine:
290 use re::engine::Plugin (
292 my ($re, $str) = @_; # $str is tainted
296 my ($re, $paren) = @_;
298 # Copy $str and untaint the copy
299 untaint(my $ret = $str);
301 # Return the untainted value
308 In either case a regex engine using perl's regex api or this module is
309 responsible for how and if it untaints its variables.
312 perlreapi, Taint::Util
317 * Engines implemented with this module don't support "s///" and "split
318 //", the appropriate parts of the "REGEXP" struct need to be wrapped
321 * Still not a complete wrapper for perlreapi in other ways, needs
322 methods for some "REGEXP" struct members, some callbacks aren't
325 * Support overloading operations on the "qr//" object, this allow
326 control over the of "qr//" objects in a manner that isn't limited by
331 '@{}' => sub { ... },
335 * Support the dispatch of arbitary methods from the re::engine::Plugin
336 qr// object to user defined subroutines via AUTOLOAD;
338 package re::engine::Plugin;
342 my ($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);
367 * Implement the dupe callback, test this on a threaded perl (and learn
368 how to use threads and how they break the current model).
370 * Allow the user to specify ->offs either as an array or a packed
371 string. Can pack() even pack I32? Only IV? int?
373 * Add tests that check for different behavior when curpm is and is not
376 * Add tests that check the refcount of the stash and other things I'm
377 mucking with, run valgrind and make sure everything is destroyed
380 * Run the debugger on the testsuite and find cases when the intuit and
381 checkstr callbacks are called. Write wrappers around them and add
387 A C compiler. This module may happen to build with a C++ compiler as
388 well, but don't rely on it, as no guarantee is made in this regard.
390 XSLoader (standard since perl 5.006).
393 Please report any bugs that aren't already listed at
394 <http://rt.cpan.org/Dist/Display.html?Queue=re-engine-Plugin> to
395 <http://rt.cpan.org/Public/Bug/Report.html?Queue=re-engine-Plugin>
398 Ævar Arnfjörð Bjarmason "<avar at cpan.org>"
400 Vincent Pit "<perl at profvince.com>"
403 Copyright 2007,2008 Ævar Arnfjörð Bjarmason.
405 Copyright 2009,2010,2011 Vincent Pit.
407 This program is free software; you can redistribute it and/or modify it
408 under the same terms as Perl itself.