This module provides an interface to the PCRE2 (Perl Compatible Regular Expression) library. This Prolog interface provides an almost complete wrapper around PCRE2 (the successor to PCRE) with as much backward compatibility to PCRE as possible, because the original implementation was for PCRE (also known as PCRE1).
Regular expressions are created from a pattern and options and represented as a SWI-Prolog blob. This implies they are subject to (atom) garbage collection. Compiled regular expressions can safely be used in multiple threads. Most predicates accept both an explicitly compiled regular expression, a pattern, or a term Pattern/Flags. The semantics of the pattern can be additionally modified by options. In the latter two cases a regular expression blob is created and stored in a cache. The cache can be cleared using re_flush/0.
Most of the predicates in this library take both a regular expression
represented as a string with optional flags, e.g., 'aap'/i
or a
compiled regular expression. If a string (+flags) alternative is
used, the library maintains a cache of compiled regular expressions. See
also
re_flush/0. The library can be
asked to rewrite the re_match/2
and
re_match/3 goals to use inlined
compiled regular expression objects using
:- set_prolog_flag(re_compile, true).
This has some consequences:
-c command line option.
?- re_match("^needle"/i, "Needle in a haystack").
true.
Defined Options are given below. For details, see the PCRE
documentation. If an option is repeated, the first value is used and
subsequent values are ignored. Unrecognized options are ignored. Unless
otherwise specified, boolean options default to
false.
If Regex is a text pattern (optionally with flags), then any of the Options for re_compile/3 can be used, in addition to the Options listed below. If Regex is the result of re_compile/3, then only the following execution-time Options are recognized and any others are ignored. Some options may not exist on your system, depending on the PCRE2 version and how it was built - these unsupported options are silently ignored.
start(From) Start at the given character indexanchored(Bool) If true, match only at the
first positionbol(Bool)
String is the beginning of a line (default true)
- affects behavior of circumflex metacharacter (^).empty(Bool) An empty string is a valid match (default true)empty_atstart(Bool) An empty string at the start of the
subject is a valid match (default true)eol(Bool)
String is the end of a line - affects behavior of dollar
metacharacter ($) (default true).newline(Mode) If any, recognize any
Unicode newline sequence, if anycrlf, recognize CR, LF, and
CRLF as newline sequences, if cr, recognize CR, if lf,
recognize LF, if crlf recognize CRLF as newline. The
default is determined by how PCRE was built, and can be found by re_config(newline2(NewlineDefault)).newline2(Mode) - synonym for newline(Mode).utf_check(Bool) - see PCRE2
API documentation You should not need this because SWI-Prolog
ensures that the UTF8 strings are valid, so the default is false.endanchored(Bool) - see PCRE2
API documentationpartial_soft(Bool) - see PCRE2
API documentationpartial_hard(Bool) - see PCRE2
API documentationdfa_restart(Bool) - see PCRE2
API documentationdfa_shortest(Bool) - see PCRE2
API documentation| Regex | is the output of re_compile/3,
a pattern or a term Pattern/Flags, where Pattern is an atom or string.
The defined flags and their related option for re_compile/3
are below.
If Regex is the output of re_compile/3, any compile-time options in Options or Flags are ignored and only match-time options are used.
The options that are derived from flags take precedence over the
options in the Options list. In the case of conflicting
flags, the first one is used (e.g., |
0. The associated value is determined by the capture_type(Type)
option passed to re_compile/3,
or by flags if Regex is of the form Pattern/Flags; and may be
specified at the level of individual captures using a naming convention
for the caption name. See
re_compile/3 for details.
The example below exploits the typed groups to parse a date specification:
?- re_matchsub("(?<date> (?<year_I>(?:\\d\\d)?\\d\\d) -
(?<month_I>\\d\\d) - (?<day_I>\\d\\d) )"/x,
"2017-04-20", Sub, []).
Sub = re_match{0:"2017-04-20", date:"2017-04-20",
day:20, month:4, year:2017}.
| Both | compilation and execution options are
processed. See
re_compile/3 and re_match/3
for the set of options. In addition, some compilation options may passed
as /Flags to Regex - see
re_match/3 for the list of flags. |
| Regex | See re_match/2 for a description of this argument. |
call(Goal, Dict1, V0, V1), call(Goal, Dict2, V1, V2), ... call(Goal, Dictn, Vn, V).
This predicate is used to implement re_split/4 and re_replace/4. For example, we can count all matches of a Regex on String using this code:
re_match_count(Regex, String, Count) :-
re_foldl(increment, Regex, String, 0, Count, []).
increment(_Match, V0, V1) :-
V1 is V0+1.
After which we can query
?- re_match_count("a", "aap", X).
X = 2.
Here is an example Goal for extracting all the matches with their offsets within the string:
range_match(Dict, StringIndex-[MatchStart-Substring|List], StringIndex-List) :-
Dict.(StringIndex.index) = MatchStart-MatchLen,
sub_string(StringIndex.string, MatchStart, MatchLen, _, Substring).
And can be used with this query (note the capture_type(range)
option, which is needed by range_match/3,
and greedy(false) to invert the meaning of *?):
?- String = "{START} Mary {END} had a {START} little lamb {END}",
re_foldl(range_match,
"{START} *?(?<piece>.*) *?{END}",
String, _{string:String,index:piece}-Matches, _-[],
[capture_type(range),greedy(false)]).
Matches = [8-"Mary", 33-"little lamb"].
?- re_split("a+", "abaac", Splits, []).
Splits = ["","a","b","aa","c"].
?- re_split(":\\s*"/n, "Age: 33", Splits, []).
Splits = ['Age', ': ', 33].
| Pattern | is the pattern text, optionally
follows by /Flags. Similar to re_matchsub/4,
the final output type can be controlled by a flag a (atom), s
(string, default) or n (number if possible, atom
otherwise). |
Throws an error if With uses a name that doesn't exist in the Pattern.
| Pattern | is the pattern text, optionally
followed by /Flags. Flags may include g, replacing all
occurences of Pattern. In addition, similar to re_matchsub/4,
the final output type can be controlled by a flag a (atom)
or s (string, default). The output type can also be
specified by the capture_type option. Capture type suffixes
can modify behavior; for example, the following will change an ISO 8601
format date (YYYY-MM-DD) to American style (m/d/y), and also remove
leading zeros by using the
_I suffix:
re_replace("(?<date> (?<year_I>(?:\\d\\d)?\\d\\d) -
(?<month_I>\\d\\d) - (?<day_I>\\d\\d) )"/x,
"$month-$day-$year",
ISODate, AmericanDate)`
|
| With | is the replacement text. It may
reference captured substrings using \N or $Name. Both N and
Name may be written as {N} and {Name} to avoid ambiguities. If a
substring is named, it cannot be referenced by its number. The single
chracters $ and \ can be escaped by doubling
(e.g., re_replace(".","$$","abc",Replaced) results in Replaced="$bc").
(Because \ is an escape character inside strings, you need
to write "\\\\" to get a single
backslash.) |
| Options | See re_match/3
for the set of options.
The options that are derived from flags take precedence over the
options in the Options list. In the case of conflicting
flags, the first one is used (e.g., |
regex
(see blob/2). Defined Options
are given below. Please consult the PCRE2
API documentation for details. If an option is repeated, the first
value is used and subsequent values are ignored. Unrecognized options
are ignored. Unless otherwise specified, boolean options default to false.
Some options may not exist on your system, depending on the PCRE2
version and how it was built - these unsupported options are silently
ignored.
The various matching predicates can take either a Regex blob or a string pattern; if they are given a string pattern, they call re_compile/3 and cache the result; so, there is little reason to use re_compile/3 directly.
anchored(Bool) If true, match only at the
first positionauto_capture(Bool) Enable use of numbered capturing
parentheses. (default true)bsr(Mode) If anycrlf, \R only
matches CR, LF or CRLF; if unicode,
\R matches all Unicode line endings.bsr2(Mode) - synonym for bsr(Mode).caseless(Bool) If true, do caseless
matching.compat(With) Error - PCRE1 had compat(javascript)
for JavaScript compatibility, but PCRE2 has removed that.dollar_endonly(Bool) If true, $ not to
match newline at enddotall(Bool) If true, . matches anything
including NLdupnames(Bool) If true, allow duplicate
names for subpatternsextended(Bool) If true, ignore white space
and # commentsfirstline(Bool) If true, force matching to
be before newlinegreedy(Bool) If true, operators such as +
and * are greedy unless followed by ?; if false,
the operators are not greedy and ? has the opposite
meaning. It can also beset by a‘(?U)` within the pattern - see the PCRE2
pattern internal option setting documentation for details and note
that the PCRE2 option is UNGREEDY, which is the inverse of
this packages greedy options. (default true)compat(With) Raises an errr - PCRE1 had compat(javascript)
for JavaScript compatibility, but PCRE2 has removed that option .
Consider using the alt_bsux and extra_alt_bsux
options.multiline(Bool) If true, ^
and $ match newlines within datanewline(Mode) If any, recognize any
Unicode newline sequence; if anycrlf (default), recognize
CR, LF, and CRLF as newline sequences; if
cr, recognize CR; if lf, recognize LF; crlf
recognize CRLF as newline; if nul, recognize the NULL
character (0x00) as newline.newline2(Mode) - synonym for newline(Mode).ucp(Bool) If true, use Unicode properties
for \d, \w, etc.utf_check(Bool) - see PCRE2
API documentation You should not need this because SWI-Prolog
ensures that the UTF8 strings are valid,endanchored(boolean) - see PCRE2
API documentationallow_empty_class(boolean) - see PCRE2
API documentationalt_bsux(boolean) - see PCRE2
API documentationauto_callout(boolean) - see PCRE2
API documentationmatch_unset_backref(boolean) - see PCRE2
API documentationnever_ucp(boolean) - see PCRE2
API documentationnever_utf(boolean) - see PCRE2
API documentationauto_possess(boolean) - see PCRE2
API documentation (default true)dotstar_anchor(boolean) - see PCRE2
API documentation (default true)start_optimize(boolean) - see PCRE2
API documentation (default true)utf(boolean) - see PCRE2
API documentationnever_backslash_c(boolean) - see PCRE2
API documentationalt_circumflex(boolean) - see PCRE2
API documentationalt_verbnames(boolean) - see PCRE2
API documentationuse_offset_limit(boolean) - see PCRE2
API documentationextended_more(boolean) - see PCRE2
API documentationliteral(boolean) - see PCRE2
API documentationmatch_invalid_utf(boolean) - see PCRE2
API documentationjit_complete(boolean) - see PCRE2
API documentationjit_partial_soft(boolean) - see PCRE2
API documentationjit_partial_hard(boolean) - see PCRE2
API documentationjit_invalid_utf(boolean) - see PCRE2
API documentationjit(boolean) - see PCRE2
API documentation (default true)copy_matched_subject(boolean) - see PCRE2
API documentationIn addition to the options above that directly map to PCRE flags the following options are processed:
optimise(Bool) or optimize(Bool) Turns on
the JIT compiler for additional optimization that greatly that speeds up
the matching performance of many patterns. (Note that he meaning has
changed slightly from the PCRE1 implementationcapture_type(+Type) How to return the matched part of
the input and possibly captured groups in there. Possible values are:
Start-Length. Note
that we use Start-Length rather than the more conventional
Start-End to allow for immediate use with sub_atom/5
and
sub_string/5.
The capture_type specifies the default for this pattern.
The interface supports a different type for each named group
using the syntax‘(?<name_T>...)`,
where T is one of S (string),
A (atom), I (integer), F (float), N
(number), T (term) and R (range). In the
current implementation I,
F and N are synonyms for T.
Future versions may act different if the parsed value is not of the
requested numeric type.
Note that re_compile/3 does not support the Pattern/Flags form that is supported by re_match/3, re_replace/4, etc.; the Pattern must be text and all compile options specified in Options.
Name(Value). Name is derived from the
PCRE_CONFIG_* constant after removing PCRE_CONFIG_
and mapping the name to lower case, e.g. utf8, unicode_properties,
etc. Value is a Prolog boolean, integer, or atom. For boolean (1 or 0)
values, true or false is returned.
re_config/1 will backtrack through all the possible configuration values if its argument is a variable. If an unknown option is specified, re_config/1 fails.
Non-compatible changes between PCRE1 and PCRE2 because numeric values
changed: bsr and newline have been replaced by bsr2
and
newline2:
bsr2 - previously bsr returned 0 or 1; now
returns unicode or anycrlfnewline2 - previously newline returned an
integer, now returns cr, lf, crlf, any, anycrlf, nulTerm values are as follows. Some values might not exist, depending on the version of PCRE2 and the options it was built with.
\R escape
sequence matches by default. Replaces bsr option from
PCRE1, which is not compatible.true if just-in-time compiling is available.cr, lf, crlf, any,
anycrlf, nul). Replaces newline
option from PCRE1, which is not compatible.trueunicodeFor backwards compatibility with PCRE1, the following are accepted, but are deprecated:
utf8 - synonym for unicodelink_size - synonym for linksizematch_limit - synonym for matchlimitparens_limit - synonym for parenslimitunicode_properties - always trueThe following have been removed because they don't exist in PCRE2 and don't seem to have any meaningful use in PCRE1:
posix_malloc_thresholdmatch_limit_recursion