PPIx::Regexp(3) User Contributed Perl Documentation PPIx::Regexp(3)
NAME
PPIx::Regexp - Represent a regular expression of some sort
SYNOPSIS
use PPIx::Regexp;
use PPIx::Regexp::Dumper;
my $re = PPIx::Regexp->new( 'qr{foo}smx' );
PPIx::Regexp::Dumper->new( $re )
->print();
INHERITANCE
"PPIx::Regexp" is a PPIx::Regexp::Node.
"PPIx::Regexp" has no descendants.
DESCRIPTION
The purpose of the PPIx-Regexp package is to parse regular expressions
in a manner similar to the way the PPI package parses Perl. This class
forms the root of the parse tree, playing a role similar to
PPI::Document.
This package shares with PPI the property of being round-trip safe.
That is,
my $expr = 's/ ( \d+ ) ( \D+ ) /$2$1/smxg';
my $re = PPIx::Regexp->new( $expr );
print $re->content() eq $expr ? "yes\n" : "no\n"
should print 'yes' for any valid regular expression.
Navigation is similar to that provided by PPI. That is to say, things
like "children", "find_first", "snext_sibling" and so on all work
pretty much the same way as in PPI.
The class hierarchy is also similar to PPI. Except for some utility
classes (the dumper, the lexer, and the tokenizer) all classes are
descended from PPIx::Regexp::Element, which provides basic navigation.
Tokens are descended from PPIx::Regexp::Token, which provides content.
All containers are descended from PPIx::Regexp::Node, which provides
for children, and all structure elements are descended from
PPIx::Regexp::Structure, which provides beginning and ending
delimiters, and a type.
There are two features of PPI that this package does not provide -
mutability and operator overloading. There are no plans for serious
mutability, though something like PPI's "prune" functionality might be
considered. Similarly there are no plans for operator overloading,
which appears to the author to represent a performance hit for little
tangible gain.
NOTICE
The use of this class to parse non-regexp quote-like strings was an
experiment that I consider failed. Therefore this use is deprecated in
favor of PPIx::QuoteLike. As of version 0.058_01, the first use of the
"parse" argument to new() resulted in a warning. As of version
0.062_01, all uses of the "parse" argument resulted in a warning. After
another six months, the "parse" argument will become fatal.
The author will attempt to preserve the documented interface, but if
the interface needs to change to correct some egregiously bad design or
implementation decision, then it will change. Any incompatible changes
will go through a deprecation cycle.
The goal of this package is to parse well-formed regular expressions
correctly. A secondary goal is not to blow up on ill-formed regular
expressions. The correct identification and characterization of ill-
formed regular expressions is not a goal of this package, nor is the
consistent parsing of ill-formed regular expressions from release to
release.
This policy attempts to track features in development releases as well
as public releases. However, features added in a development release
and then removed before the next production release will not be
tracked, and any functionality relating to such features will be
removed. The issue here is the potential re-use (with different
semantics) of syntax that did not make it into the production release.
From time to time the Perl regular expression engine changes in ways
that change the parse of a given regular expression. When these changes
occur, "PPIx::Regexp" will be changed to produce the more modern parse.
Known examples of this include:
$( no longer interpolates as of Perl 5.005, per "perl5005delta".
Newer Perls seem to parse this as "qr{$}" (i.e. and end-of-string
or newline assertion) followed by an open parenthesis, and that is
what "PPIx::Regexp" does.
$) and $| also seem to parse as the "$" assertion
followed by the relevant meta-character, though I have no
documentation reference for this.
"@+" and "@-" no longer interpolate as of Perl 5.9.4
per "perl594delta". Subsequent Perls treat "@+" as a quantified
literal and "@-" as two literals, and that is what "PPIx::Regexp"
does. Note that subscripted references to these arrays do
interpolate, and are so parsed by "PPIx::Regexp".
Only space and horizontal tab are whitespace as of Perl 5.23.4
when inside a bracketed character class inside an extended
bracketed character class, per "perl5234delta". Formerly any white
space character parsed as whitespace. This change in "PPIx::Regexp"
will be reverted if the change in Perl does not make it into Perl
5.24.0.
Unescaped literal left curly brackets
These are being removed in positions where quantifiers are legal,
so that they can be used for new functionality. Some of them are
gone in 5.25.1, others will be removed in a future version of Perl.
In situations where they have been removed, perl_version_removed()
will return the version in which they were removed. When the new
functionality appears, the parse produced by this software will
reflect the new functionality.
NOTE that the situation with a literal left curly after a literal
character is complicated. It was made an error in Perl 5.25.1, and
remained so through all 5.26 releases, but became a warning again
in 5.27.1 due to its use in GNU Autoconf. Whether it will ever
become illegal again is not clear to me based on the contents of
perl5271delta. At the moment perl_version_removed() returns
"undef", but obviously that is not the whole story, and methods
accepts_perl() and requirements_for_perl() were introduced to deal
with this complication.
"\o{...}"
is parsed as the octal equivalent of "\x{...}". This is its meaning
as of perl 5.13.2. Before 5.13.2 it was simply literal 'o' and so
on.
There are very probably other examples of this. When they come to light
they will be documented as producing the modern parse, and the code
modified to produce this parse if necessary.
METHODS
This class provides the following public methods. Methods not
documented here are private, and unsupported in the sense that the
author reserves the right to change or remove them without notice.
new
my $re = PPIx::Regexp->new('/foo/');
This method instantiates a "PPIx::Regexp" object from a string, a
PPI::Token::QuoteLike::Regexp, a PPI::Token::Regexp::Match, or a
PPI::Token::Regexp::Substitute. Honestly, any PPI::Element will work,
but only the three Regexp classes mentioned previously are likely to do
anything useful.
Whatever form the argument takes, it is assumed to consist entirely of
a valid match, substitution, or "qr<>" string.
Optionally you can pass one or more name/value pairs after the regular
expression. The possible options are:
default_modifiers array_reference
This option specifies a reference to an array of default modifiers
to apply to the regular expression being parsed. Each modifier is
specified as a string. Any actual modifiers found supersede the
defaults.
When applying the defaults, '?' and '/' are completely ignored, and
'^' is ignored unless it occurs at the beginning of the modifier.
The first dash ('-') causes subsequent modifiers to be negated.
So, for example, if you wish to produce a "PPIx::Regexp" object
representing the regular expression in
use re '/smx';
{
no re '/x';
m/ foo /;
}
you would (after some help from PPI in finding the relevant
statements), do something like
my $re = PPIx::Regexp->new( 'm/ foo /',
default_modifiers => [ '/smx', '-/x' ] );
encoding name
This option specifies the encoding of the regular expression. This
is passed to the tokenizer, which will "decode" the regular
expression string before it tokenizes it. For example:
my $re = PPIx::Regexp->new( '/foo/',
encoding => 'iso-8859-1',
);
parse parse_type
This option specifies what kind of parse is to be done. Possible
values are 'regex', 'string', or 'guess'. Any value but 'regex' is
experimental.
As it turns out, I consider parsing non-regexp quote-like things
with this class to be a failed experiment, and the relevant
functionality is being deprecated and removed in favor of
PPIx::QuoteLike. See above for details.
If 'regex' is specified, the first argument is expected to be a
valid regex, and parsed as though it were.
If 'string' is specified, the first argument is expected to be a
valid string literal and parsed as such. The return is still a
"PPIx::Regexp" object, but the regular_expression() and modifier()
methods return nothing, and the replacement() method returns the
content of the string.
If 'guess' is specified, this method will try to guess what the
first argument is. If the first argument is a PPI::Element, the
guess will reflect the PPI parse. But the guess can be wrong if the
first argument is a string representing an unusually-delimited
regex. For example, 'guess' will parse "foo" as a string, but Perl
will parse it as a regex if preceded by a regex binding operator
(e.g. "$x =~ "foo""), as shown by
perl -MO=Deparse -e '$x =~ "foo"'
which prints
$x =~ /foo/u
under Perl 5.22.0.
The default is 'regex'.
postderef boolean
This option is passed on to the tokenizer, where it specifies
whether postfix dereferences are recognized in interpolations and
code. This experimental feature was introduced in Perl 5.19.5.
The default is the value of
$PPIx::Regexp::Tokenizer::DEFAULT_POSTDEREF, which is true. When
originally introduced this was false, but was documented as
becoming true when and if postfix dereferencing became mainstream.
The intent to mainstream was announced with Perl 5.23.1, and
became official (so to speak) with Perl 5.24.0, so the default
became true with PPIx::Regexp 0.049_01.
Note that if PPI starts unconditionally recognizing postfix
dereferences, this argument will immediately become ignored, and
will be put through a deprecation cycle and removed.
strict boolean
This option is passed on to the tokenizer and lexer, where it
specifies whether the parse should assume "use re 'strict'" is in
effect.
The 'strict' pragma was introduced in Perl 5.22, and its
documentation says that it is experimental, and that there is no
commitment to backward compatibility. The same applies to the parse
produced when this option is asserted. Also, the usual caveat
applies: if "use re 'strict'" ends up being retracted, this option
and all related functionality will be also.
Given the nature of "use re 'strict'", you should expect that if
you assert this option, regular expressions that previously parsed
without error might no longer do so. If an element ends up being
declared an error because this option is set, its
"perl_version_introduced()" will be the Perl version at which "use
re 'strict'" started rejecting these elements.
The default is false.
trace number
If greater than zero, this option causes trace output from the
parse. The author reserves the right to change or eliminate this
without notice.
Passing optional input other than the above is not an error, but
neither is it supported.
new_from_cache
This static method wraps "new" in a caching mechanism. Only one object
will be generated for a given PPI::Element, no matter how many times
this method is called. Calls after the first for a given PPI::Element
simply return the same "PPIx::Regexp" object.
When the "PPIx::Regexp" object is returned from cache, the values of
the optional arguments are ignored.
Calls to this method with the regular expression in a string rather
than a PPI::Element will not be cached.
Caveat: This method is provided for code like Perl::Critic which might
instantiate the same object multiple times. The cache will persist
until "flush_cache" is called.
flush_cache
$re->flush_cache(); # Remove $re from cache
PPIx::Regexp->flush_cache(); # Empty the cache
This method flushes the cache used by "new_from_cache". If called as a
static method with no arguments, the entire cache is emptied. Otherwise
any objects specified are removed from the cache.
capture_names
foreach my $name ( $re->capture_names() ) {
print "Capture name '$name'\n";
}
This convenience method returns the capture names found in the regular
expression.
This method is equivalent to
$self->regular_expression()->capture_names();
except that if "$self->regular_expression()" returns "undef" (meaning
that something went terribly wrong with the parse) this method will
simply return.
delimiters
print join("\t", PPIx::Regexp->new('s/foo/bar/')->delimiters());
# prints '// //'
When called in list context, this method returns either one or two
strings, depending on whether the parsed expression has a replacement
string. In the case of non-bracketed substitutions, the start delimiter
of the replacement string is considered to be the same as its finish
delimiter, as illustrated by the above example.
When called in scalar context, you get the delimiters of the regular
expression; that is, element 0 of the array that is returned in list
context.
Optionally, you can pass an index value and the corresponding
delimiters will be returned; index 0 represents the regular
expression's delimiters, and index 1 represents the replacement
string's delimiters, which may be undef. For example,
print PPIx::Regexp->new('s{foo}<bar>')->delimiters(1);
# prints '<>'
If the object was not initialized with a valid regexp of some sort, the
results of this method are undefined.
errstr
This static method returns the error string from the most recent
attempt to instantiate a "PPIx::Regexp". It will be "undef" if the most
recent attempt succeeded.
extract_regexps
my $doc = PPI::Document->new( $path );
$doc->index_locations();
my @res = PPIx::Regexp->extract_regexps( $doc )
This convenience (well, sort-of) static method takes as its argument a
PPI::Document object and returns "PPIx::Regexp" objects corresponding
to all regular expressions found in it, in the order in which they
occur in the document. You will need to keep a reference to the
original PPI::Document object if you wish to be able to recover the
original PPI::Element objects via the PPIx::Regexp source() method.
failures
print "There were ", $re->failures(), " parse failures\n";
This method returns the number of parse failures. This is a count of
the number of unknown tokens plus the number of unterminated structures
plus the number of unmatched right brackets of any sort.
max_capture_number
print "Highest used capture number ",
$re->max_capture_number(), "\n";
This convenience method returns the highest capture number used by the
regular expression. If there are no captures, the return will be 0.
This method is equivalent to
$self->regular_expression()->max_capture_number();
except that if "$self->regular_expression()" returns "undef" (meaning
that something went terribly wrong with the parse) this method will
too.
modifier
my $re = PPIx::Regexp->new( 's/(foo)/${1}bar/smx' );
print $re->modifier()->content(), "\n";
# prints 'smx'.
This method retrieves the modifier of the object. This comes from the
end of the initializing string or object and will be a
PPIx::Regexp::Token::Modifier.
Note that this object represents the actual modifiers present on the
regexp, and does not take into account any that may have been applied
by default (i.e. via the "default_modifiers" argument to "new()"). For
something that takes account of default modifiers, see
modifier_asserted(), below.
In the event of a parse failure, there may not be a modifier present,
in which case nothing is returned.
modifier_asserted
my $re = PPIx::Regexp->new( '/ . /',
default_modifiers => [ 'smx' ] );
print $re->modifier_asserted( 'x' ) ? "yes\n" : "no\n";
# prints 'yes'.
This method returns true if the given modifier is asserted for the
regexp, whether explicitly or by the modifiers passed in the
"default_modifiers" argument.
Starting with version 0.036_01, if the argument is a single-character
modifier followed by an asterisk (intended as a wild card character),
the return is the number of times that modifier appears. In this case
an exception will be thrown if you specify a multi-character modifier
(e.g. 'ee*'), or if you specify one of the match semantics modifiers
(e.g. 'a*').
regular_expression
my $re = PPIx::Regexp->new( 's/(foo)/${1}bar/smx' );
print $re->regular_expression()->content(), "\n";
# prints '/(foo)/'.
This method returns that portion of the object which actually
represents a regular expression.
replacement
my $re = PPIx::Regexp->new( 's/(foo)/${1}bar/smx' );
print $re->replacement()->content(), "\n";
# prints '${1}bar/'.
This method returns that portion of the object which represents the
replacement string. This will be "undef" unless the regular expression
actually has a replacement string. Delimiters will be included, but
there will be no beginning delimiter unless the regular expression was
bracketed.
source
my $source = $re->source();
This method returns the object or string that was used to instantiate
the object.
type
my $re = PPIx::Regexp->new( 's/(foo)/${1}bar/smx' );
print $re->type()->content(), "\n";
# prints 's'.
This method retrieves the type of the object. This comes from the
beginning of the initializing string or object, and will be a
PPIx::Regexp::Token::Structure whose "content" is one of 's', 'm',
'qr', or ''.
RESTRICTIONS
By the nature of this module, it is never going to get everything
right. Many of the known problem areas involve interpolations one way
or another.
Ambiguous Syntax
Perl's regular expressions contain cases where the syntax is ambiguous.
A particularly egregious example is an interpolation followed by square
or curly brackets, for example $foo[...]. There is nothing in the
syntax to say whether the programmer wanted to interpolate an element
of array @foo, or whether he wanted to interpolate scalar $foo, and
then follow that interpolation by a character class.
The perlop documentation notes that in this case what Perl does is to
guess. That is, it employs various heuristics on the code to try to
figure out what the programmer wanted. These heuristics are documented
as being undocumented (!) and subject to change without notice. As an
example of the problems even perl faces in parsing Perl, see
<https://rt.perl.org/Public/Bug/Display.html?id=133027>.
Given this situation, this module's chances of duplicating every Perl
version's interpretation of every regular expression are pretty much
nil. What it does now is to assume that square brackets containing
only an integer or an interpolation represent a subscript; otherwise
they represent a character class. Similarly, curly brackets containing
only a bareword or an interpolation are a subscript; otherwise they
represent a quantifier.
Changes in Syntax
Sometimes the introduction of new syntax changes the way a regular
expression is parsed. For example, the "\v" character class was
introduced in Perl 5.9.5. But it did not represent a syntax error prior
to that version of Perl, it was simply parsed as "v". So
$ perl -le 'print "v" =~ m/\v/ ? "yes" : "no"'
prints "yes" under Perl 5.8.9, but "no" under 5.10.0. "PPIx::Regexp"
generally assumes the more modern parse in cases like this.
Equivocation
Very occasionally, a construction will be removed and then added back
-- and then, conceivably, removed again. In this case, the plan is for
perl_version_introduced() to return the earliest version in which the
construction appeared, and perl_version_removed() to return the version
after the last version in which it appeared (whether production or
development), or "undef" if it is in the highest-numbered Perl.
The constructions involved in this are:
Un-escaped literal left curly after literal
That is, something like "qr<x{>".
This was made an error in 5.25.1, and it was an error in 5.26.0. But
it became a warning again in 5.27.1. The perl5271delta says it was re-
instated because the changes broke GNU Autoconf, and the warning
message says it will be removed in Perl 5.30.
Accordingly, perl_version_introduced() returns 5.0. At the moment
perl_version_removed() returns '5.025001'. But if it is present with or
without warning in 5.28, perl_version_removed() will become "undef". If
you need finer resolution than this, see PPIx::Regexp::Element methods
l<accepts_perl()|PPIx::Regexp::Element/accepts_perl> and
l<requirements_for_perl()|PPIx::Regexp::Element/requirements_for_perl>
Static Parsing
It is well known that Perl can not be statically parsed. That is, you
can not completely parse a piece of Perl code without executing that
same code.
Nevertheless, this class is trying to statically parse regular
expressions. The main problem with this is that there is no way to know
what is being interpolated into the regular expression by an
interpolated variable. This is a problem because the interpolated value
can change the interpretation of adjacent elements.
This module deals with this by making assumptions about what is in an
interpolated variable. These assumptions will not be enumerated here,
but in general the principal is to assume the interpolated value does
not change the interpretation of the regular expression. For example,
my $foo = 'a-z]';
my $re = qr{[$foo};
is fine with the Perl interpreter, but will confuse the dickens out of
this module. Similarly and more usefully, something like
my $mods = 'i';
my $re = qr{(?$mods:foo)};
or maybe
my $mods = 'i';
my $re = qr{(?$mods)$foo};
probably sets a modifier of some sort, and that is how this module
interprets it. If the interpolation is not about modifiers, this module
will get it wrong. Another such semi-benign example is
my $foo = $] >= 5.010 ? '?<foo>' : '';
my $re = qr{($foo\w+)};
which will parse, but this module will never realize that it might be
looking at a named capture.
Non-Standard Syntax
There are modules out there that alter the syntax of Perl. If the
syntax of a regular expression is altered, this module has no way to
understand that it has been altered, much less to adapt to the
alteration. The following modules are known to cause problems:
Acme::PerlML, which renders Perl as XML.
"Data::PostfixDeref", which causes Perl to interpret suffixed empty
brackets as dereferencing the thing they suffix. This module by Ben
Morrow ("BMORROW") appears to have been retracted.
Filter::Trigraph, which recognizes ANSI C trigraphs, allowing Perl to
be written in the ISO 646 character set.
Perl6::Pugs. Enough said.
Perl6::Rules, which back-ports some of the Perl 6 regular expression
syntax to Perl 5.
Regexp::Extended, which extends regular expressions in various ways,
some of which seem to conflict with Perl 5.010.
SEE ALSO
Regexp::Parsertron(3), which uses Marpa::R2 to parse the regexp, and
Tree(3) for navigation. Unlike "PPIx::Regexp|PPIx::Regexp",
Regexp::Parsertron(3) supports modification of the parse tree.
Regexp::Parser(3), which parses a bare regular expression (without
enclosing "qr{}", "m//", or whatever) and uses a different navigation
model. After a long hiatus, this module has been adopted, and is again
supported.
SUPPORT
Support is by the author. Please file bug reports at
<http://rt.cpan.org>, or in electronic mail to the author.
AUTHOR
Thomas R. Wyant, III wyant at cpan dot org
COPYRIGHT AND LICENSE
Copyright (C) 2009-2019 by Thomas R. Wyant, III
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl 5.10.0. For more details, see the full
text of the licenses in the directory LICENSES.
This program is distributed in the hope that it will be useful, but
without any warranty; without even the implied warranty of
merchantability or fitness for a particular purpose.
perl v5.28.2 2019-08-18 PPIx::Regexp(3)
ppix-regexp 0.66.0 - Generated Mon Aug 19 16:31:07 CDT 2019