NAME
    List::Prefixed - Prefixed String List

SYNOPSIS
      use List::Prefixed;

      # construct a new prefixed tree
      $folded = List::Prefixed->fold(qw( Fu Foo For Form Foot Food Ba Bar Baz ));

      # get all items sharing a common prefix
      @list = $folded->list('Fo'); # Foo, Food, Foot, For, Form

      # serialize as regular expression
      $regex = $folded->regex; # '(?:Ba(?:r|z)?|F(?:o(?:o(?:d|t)?|r(?:m)?)|u))'

      # de-serialize from regular expression
      $unfolded = List::Prefixed->unfold($regex);

DESCRIPTION
    The idea of a *Prefixed List* comes from regular expressions determining
    a finite list of words, like this:

      /(?:Ba(?:r|z)?|F(?:o(?:o(?:d|t)?|r(?:m)?)|u))/

    The expression above matches exactly these strings:

      "Ba", "Bar", "Baz", "Foo", "Food", "Foot", "For", "Form", "Fu".

    Representing a string list that way can have some advantages in certain
    situations:

    *   The regular expression provides efficient test methods on arbitrary
        strings (e.g. whether or not a string is contained in the list or
        starts or ends with an element from the list).

    *   The representaion is compressing, depending on how many shared
        prefixes appear in a list.

    *   Conversely, a prefixed list can be efficiently set up from such a
        regular expression. Thus, the prefixed list leads to a natural way
        of serialization and de-serialization.

    *   Sub lists sharing a common prefix can be extracted efficently from a
        prefixed list. This leads to an efficient implementation of
        auto-completion.

    For example, from the Perl package names
    <https://cpan.metacpan.org/modules/02packages.details.txt> indexed on
    CPAN, one can get a list of about 82K module names that takes about 2.1M
    data. "List::Prefixed" can create a regular expression of about 900K
    that matches exactly these names.

    A *Prefixed List* is a tree consisting of node triples, formally defined
    as follows:

      node: ( prefix [node-list] opt )
        where:
          prefix: String
          node-list: List of node
          opt: Boolean

    The list elements are the prefix strings, each of them appended to the
    prefix of the parent node. The "opt" flag is true if the list of sub
    nodes is optional, i.e., if the node prefix appended together with the
    parent prefixes is also contained in the list itself.

    Any string list has a trivial representation that way, if one takes each
    string as the prefix of a node with empty node-list and collects all
    these nodes into a parent node with empty prefix.

    A prefixed tree is called *folded*, if it's in minimal form, i.e. if
    there are no two child nodes in a parent node sharing a common left part
    in their prefixes. Obviously, for each string list, there exists a
    unique folded *Prefixed Tree* representation.

METHODS
  new
      $prefixed = List::Prefixed->new( @list );

    This is an alias of the fold method.

  fold
      $prefixed = List::Prefixed->fold( @list );

    Constructs a new folded "List::Prefixed" tree from the given string
    list.

  unfold
      $prefixed = List::Prefixed->unfold( $regex );

    Constructs a new "List::Prefixed" tree from a regular expression string.
    The string argument shuld be obtained from the regex method.

  list
      @list = $prefixed->list;
      @list = $prefixed->list( $string );

    Returns the list of list elements starting with the given string if a
    string argument is present or the whole list otherwise. In scalar
    context an ARRAY reference is returned.

  regex
      $regex = $prefixed->regex;

    Returns a minimized regular expression (as string) matching exactly the
    strings the object has been constructed with.

    You can control the escaping style of the expression. The default
    behavior is to apply Perl's quotemeta
    <http://perldoc.perl.org/functions/quotemeta.html> function and replace
    any non-ASCII character with "\x{FFFF}", where "FFFF" is the hexadecimal
    character code. This is the Perl-compatible or PCRE style. To obtain an
    expression compatible with Java and the like, use

      use List::Prefixed uc_escape_style => 'Java'; # \uFFFF style

    To skip Unicode escaping completely, use

      use List::Prefixed uc_escape_style => undef;  # do not escape

    Alternatively, you can control the style at runtime by way of
    configuration variables.

CONFIGURATION VARIABLES
    *$UC_ESCAPE_STYLE*
        Controls the escaping style for Unicode (non-ASCII) characters. The
        value can be one of the following:

        'PCRE'
            Default style "\x{FFFF}"

        'Java'
            Java etc. style "\uFFFF"

        "undef"
            Do not escape Unicode characters at all. This may result in
            shorter expressions but may cause encoding issues under some
            circumstances.

    *$REGEX_ESCAPE*, *$REGEX_UNESCAPE*
        By providing string functions one can customize the escaping
        behavior arbitrarily. In this case, $UC_ESCAPE_STYLE has no effect.

KNOWN BUGS
    The term *prefix* refers to the storage order of characters. That is,
    prefix filtering with right-to-left written Unicode strings (such as
    Arabic or Hebrew) goes to the wrong direction from the user's point of
    view.

    Large lists may cause deep recursion within the fold method. To avoid a
    lot of Deep recursion on anonymous subroutine
    <http://perldoc.perl.org/perldiag.html> warnings, there is a "no
    warnings 'recursion'" directive in place. This is worth mentioning,
    though it's not actually a bug.

EXPORT
    Strictly OO, exports nothing.

REPOSITORY
    <https://github.com/boethin/List-Prefixed>

AUTHOR
    Sebastian Böthin, <boethin@xn--domain.net>

COPYRIGHT AND LICENSE
    Copyright (C) 2015 by Sebastian Böthin

    This library is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself, either Perl version 5.14.2 or, at
    your option, any later version of Perl 5 you may have available.

