pcre.pl -- Perl compatible regular expression matching for SWI-Prolog

This module provides an interface to the PCRE (Perl Compatible Regular Expression) library. This Prolog interface provides an almost comprehensive wrapper around PCRE.

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. 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.

See also: - `man pcre` for details.

re_match(+Regex, +String) is semidet

re_match(+Regex, +String, +Options) is semidet

Succeeds if String matches Regex. For example:

?- re_match("^needle"/i, "Needle in a haystack").
true.

Options:

anchored(Bool): If true, match only at the first position
bol(Bool): Subject string is the beginning of a line (default false)
bsr(Mode): If anycrlf, \R only matches CR, LF or CRLF. If unicode, \R matches all Unicode line endings. Subject string is the end of a line (default false)
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): Subject string is the end of a line (default false)
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 and finally if crlf recognize CRLF as newline.
start(+From): Start at the given character index

Arguments:

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 there related option for re_compile/3 are below.

x: extended(true)
i: caseless(true)
m: multiline(true)
s: dotall(true)
a: capture_type(atom)
r: capture_type(range)
t: capture_type(term)

re_matchsub(+Regex, +String, -Sub:dict, +Options) is semidet

Match String against Regex. On success, Sub is a dict containing integer keys for the numbered capture group and atom keys for the named capture groups. The associated value is determined by the capture_type(Type) option passed to re_compile/3, may be specified using 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) )"/e,
               "2017-04-20", Sub, []).
Sub = re_match{0:"2017-04-20", date:"2017-04-20",
               day:20, month:4, year:2017}.

Arguments:

`Options`	- Only execution options are processed. See re_match/3 for the set of options. Compilation options must be passed as `/flags` to `Regex`.
`Regex`	- See re_match/2 for a description of this argument.

re_foldl(:Goal, +Regex, +String, ?V0, ?V, +Options) is semidet

Fold all matches of Regex on String. Each match is represented by a dict as specified for re_matchsub/4. V0 and V are related using a sequence of invocations of Goal as illustrated below.

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.

re_split(+Pattern, +String, -Split:list) is det

re_split(+Pattern, +String, -Split:list, +Options) is det

Split String using the regular expression Pattern. Split is a list of strings holding alternating matches of Pattern and skipped parts of the String, starting with a skipped part. The Split lists ends with a string of the content of String after the last match. If Pattern does not appear in String, Split is a list holding a copy of String. This implies the number of elements in Split is always odd. For example:

?- re_split("a+", "abaac", Split, []).
Split = ["","a","b","aa","c"].
?- re_split(":\\s*"/n, "Age: 33", Split, []).
Split = ['Age', ': ', 33].

Arguments:

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).

re_replace(+Pattern, +With, +String, -NewString)

Replace matches of the regular expression Pattern in String with With. With may reference captured substrings using \N or $Name. Both N and Name may be written as {N} and {Name} to avoid ambiguities.

Arguments:

Pattern - is the pattern text, optionally follows 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).

compile_replacement(+With, -Compiled)[private]

Compile the replacement specification into a specification that can be processed quickly. The compiled expressions are cached and may be reclaimed using re_flush/0.

re_compile(+Pattern, -Regex, +Options) is det

Compiles Pattern to a Regex blob of type regex (see blob/2). Defined Options are defined below. Please consult the PCRE documentation for details.

anchored(Bool): Force pattern anchoring
bsr(Mode): If anycrlf, \R only matches CR, LF or CRLF. If unicode, \R matches all Unicode line endings.
caseless(Bool): If true, do caseless matching.
dollar_endonly(Bool): If true, $ not to match newline at end
dotall(Bool): If true, . matches anything including NL
dupnames(Bool): If true, allow duplicate names for subpatterns
extended(Bool): If true, ignore white space and # comments
extra(Bool): If true, PCRE extra features (not much use currently)
firstline(Bool): If true, force matching to be before newline
compat(With): If javascript, JavaScript compatibility
multiline(Bool): If true, ^ and $ match newlines within data
newline(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 and finally if crlf recognize CRLF as newline.
ucp(Bool): If true, use Unicode properties for \d, \w, etc.
ungreedy(Bool): If true, invert greediness of quantifiers

In addition to the options above that directly map to pcre flags the following options are processed:

optimize(Bool)

If true, study the regular expression.

capture_type(+Type)

How to return the matched part of the input and possibly captured groups in there. Possible values are:

string: Return the captured string as a string (default).
atom: Return the captured string as an atom.
range: Return the captured string as a pair Start-Length. Note the we use Start-Length` rather than the more conventional Start-End to allow for immediate use with sub_atom/5 and sub_string/5.
term: Parse the captured string as a Prolog term. This is notably practical if you capture a number.

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.

re_compiled(+Spec, --Regex) is det[private]

Create a compiled regex from a specification. Cached compiled regular expressions can be reclaimed using re_flush/0.

re_flush

Clean pattern and replacement caches.

To be done: - Flush automatically if the cache becomes too large.

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

re_split(Arg1, Arg2, Arg3, Arg4)
re_config(Arg1)
re_match(Arg1, Arg2, Arg3)