NAME
    YAML::Active - Combine data and logic in YAML

VERSION
    version 1.100810

SYNOPSIS
      use YAML::Active;
      my $data = Load(<<'EOYAML');
      pid: /YAML::Active::PID
        doit:
      foo: bar
      include_test: /YAML::Active::Include
          filename: t/testperson.yaml
      ticket_no: /YAML::Active::Concat
        - '20010101.1234'
        - /YAML::Active::PID
          doit:
        - /YAML::Active::Eval
          code: sub { sprintf "%04d", ++(our $cnt) }
      setup:
        1: /Registry::YAML::Active::WritePerson
           person:
             personname: Foobar
             handle: AB123456-NICAT
        2: /Registry::YAML::Active::WritePerson
           person: /YAML::Active::Include
             filename: t/testperson.yaml
      EOYAML

DESCRIPTION
    YAML is an intuitive way to describe nested data structures. This module
    extends YAML's capabilities so that it ceases to be a static data
    structure and become something more active, with data and logic
    combined. This makes the logic reusable since it is bound to the data
    structure. Without "YAML::Active", you have to load the YAML data, then
    process it in some way. The logic describing which parts of the data
    have to be processed and how was separated from the data. Using
    "YAML::Active", the description of how to process the data can be
    encapsulated in the data structure itself.

    The way this works is to assign a transfer type to the YAML nodes you
    want to process. The transfer type refers to a Perl package which is
    expected to have a "yaml_active()" method which contains the logic; you
    can think of the array or hash structure below that node as the
    subroutine's arguments.

    "YAML::Active" provides its own "Load()" and "LoadFile()" subroutines
    which work like the subroutines of the same name in "YAML", except that
    they also traverse the whole data structure, recognizing packages named
    as transfer types that have a "yaml_active()" method and calling that
    method on the given node.

    An example:

      some_string: /YAML::Active::Concat
        - foo
        - bar
        - baz

    defines a hash key whose value is an active YAML element. When you call
    "YAML::Active"'s "Load()" on that data, at some point the hash value is
    being encountered. The "YAML::Active::Concat" plugin (as a convenience
    also defined in the same file as "YAML::Active") has a "yaml_active()"
    method which expects to be called on an array reference (that is, the
    thing blessed into "YAML::Active::Concat" is expected to be an array
    reference). The method in turn activates all of the array's elements and
    joins the results. So after loading the data structure, the result is
    equivalent to

      some_string: foobarbaz

    Because "YAML::Active::Concat" also activates all of its arguments, you
    can nest activation logic:

      some_string /YAML::Active::Concat
        - foo
        - /YAML::Active::PID
          doit:
        - /YAML::Active::Eval
          code: sub { sprintf "%04d", ++(our $cnt) }

    This active YAML uses two more plugins, "YAML::Active::PID" and
    "YAML::Active::Eval". "YAML::Active::PID" replaces its node with the
    current process's id. Note that even though this plugin doesn't need any
    arguments, we have to provide something - anything, in fact, whether it
    be an array reference or a hash reference, because YAML can bless only
    references. "YAML::Active::Eval" expects a hash reference with a "code"
    key whose value is the source code for an anonymous sub which the plugin
    calls and whose return value it uses to replace the activated node.

    An activation plugin (that is, a package referred to by a node's
    transfer type) can have any name, but if that name contains the string
    "YAML::Active", it is being "required()" if it doesn't already provide a
    "yaml_active()" method. This is merely a convenience so you don't have
    to "use()" or "require()" the packages beforehand and things work a bit
    more transparently. If you merely want to bless a node (that is, provide
    a transfer type) into a package that's not an activation plugin, be sure
    that the package name doesn't contain the string "YAML::Active".

FUNCTIONS
  Load
    Like "YAML"'s "Load()", but activates the data structure after loading
    it and returns the activated data structure.

  Load_inactive
    Like "YAML"'s "Load()", it doesn't activate the data structure.

  Dump
    Like "YAML"'s "Dump()".

  Reload
    Dumps, then loads the data structure and returns the result.

  LoadFile
    Like "YAML"'s "LoadFile()", but activates the data structure after
    loading it and returns the activated data structure.

  node_activate
    Expects a reference and recursively activates it, returning the
    resulting reference.

    If it encounters an array, it calls "array_activate()" on the node and
    returns the result.

    If it encounters a hash, it calls "hash_activate()" on the node and
    returns the result.

    If it encounters a node that can be activated (i.e., that is blessed
    into a package that has a "yaml_activate()" method, it activates the
    node and returns the result. If the package name contains the string
    "YAML::Active" and it doesn't have a "yaml_activate()" method,
    "node_activate()" tries to "require()" the package (as a convenience).
    That is, if you want to write a plugin, you can either include the
    string "YAML::Active" somewhere in its package name, or use any other
    name but then you'd have to "use()" or "require()" it before activating
    some YAML.

    Otherwise it just returns the node as it could be an unblessed scalar or
    a reference blessed into a package that's got nothing to do with
    activation.

  array_activate
    Takes an array reference and activates every array element in turn, then
    returns a new array references containing the results. Null elements
    (that is, elements blessed into "YAML::Active::NULL") are ignored.

  hash_activate
    Takes a hash reference and activates every value, then returns a new
    hash references containing the results (the hash keys are left alone).
    Keys with null values (that is, values blessed into
    "YAML::Active::NULL") are ignored.

  assert_arrayref
    Checks that its argument is an array reference. If not, "die()"s
    reporting the caller.

  assert_hashref
    Checks that its argument is a hash reference. If not, "die()"s reporting
    the caller.

  yaml_NULL
    Returns an empty hash reference blessed into the "YAML::Active::NULL"
    package. This function is used by side-effect-only plugins that don't
    want to have a trace of their existence left in the activated data
    structure. For an example see the "YAML::Active::Print".

  NULL
    This is a constant with the value "YAML::Active::NULL".

  node_dump
    Dumps a data structure node. It is used by "Dump()". It calls
    "array_dump()" and "hash_dump()" as necessary. For scalar nodes, if the
    node is a blessed reference and the package it is blessed into has a
    "prepare_dump()" function, that function is called. Then, if the package
    has a "yaml_dump()" function, that function is called as well. After the
    recursive dump is finished, each package that had a "prepare_dump()"
    function is checked for a "finish_dump()" function, which is called if
    it exists.

  array_dump
    Dumps an array reference node. It is called by "node_dump()" and calls
    "node_dump()" itself on the array elements.

  hash_dump
    Dumps a hash reference node. It is called by "node_dump()" and calls
    "node_dump()" itself on the hash values.

  should_process_node_in_phase
    Takes as arguments a node and optionally a phase. If the phase argument
    is given, return true for those nodes that have this phase requirements.
    If the phase argument is not given, return true for those nodes that
    don't have a phase requirements.

EXPORT
    Nothing is exported by default, but you can request each of the
    subroutines individually or grouped by tags. The tags and their symbols
    are, in YAML notation:

      load:
        - Load
        - LoadFile
      active:
        - node_activate
        - array_activate
        - hash_activate
      assert:
        - assert_arrayref
        - assert_hashref
      null:
        - yaml_NULL
        - NULL

    There is also the "all" tag, which contains all of the above symbols.

DEFAULT PLUGINS
    "YAML::Active::Concat"
        Expects an array reference and joins the activated array elements,
        returning the joined string.

        For an example, see the DESCRIPTION above.

    "YAML::Active::Eval"
        Expects a hash reference with a "code" key. "eval"s the activated
        hash value returns the result from executing the coderef (passing no
        arguments).

        Example:

          - /YAML::Active::Eval
            code: sub { sprintf "%04d", ++(our $cnt) }

        Result:

          - 1

        At least, that's the answer the first time around.

    "YAML::Active::Include"
        Expects a hash reference with a "filename" key. Calls
        "YAML::Active"'s "LoadFile()" on the activated filename. That is,
        the filename can itself use an activation plugin, and the file
        contents are activated as well.

        Example:

          description: /YAML::Active::Include
            filename: description.yaml

        Result:

          description: >
            The content of the included file goes here.

    "YAML::Active::PID"
        Returns the current process id.

        Example:

          the_pid: /YAML::Active::PID
            whatever:

        Result (for example):

          the_pid: 12345

        Note that, although this plugin doesn't require any arguments, we
        have to give it either an array reference or a hash reference,
        because "YAML" can't bless something that's not a reference. The
        contents of the reference don't matter.

    "YAML::Active::Shuffle"
        Expects an array reference and returns another array reference with
        the activated original elements in random order.

        Example:

          data: /YAML::Active::Shuffle
                - 1
                - 2
                - 3
                - 4
                - 5

        Result (for example):

          data:
            - 3
            - 5
            - 1
            - 2
            - 4

    "YAML::Active::Print"
        Expects an array reference and joins the activated array elements,
        printing the result and returning a null (i.e., a
        "YAML::Active::NULL") node. That is, the node won't appear in the
        resulting activated data structure.

        Example:

          data:
            - foo
            - /YAML::Active::Print
               - '# Hello, world!'
               - 'Goodbye, world!'
            - baz

        Result:

          data:
            - foo
            - baz

        and the string "# Hello, world!Goodbye, world!" is printed.

    "YAML::Active::uc"
        Replaces node values (scalars, array elements and hash values) with
        their lowercased value. Does not descend into deeper array
        references or hash references, but passes them through unaltered.

        Example:

          data: /YAML::Active::uc
            - Hello
            - world and
            - one: GOoD
              two: byE
            - wOrLd!

        Result:

          data:
            - HELLO
            - WORLD AND
            - one: GOoD
              two: byE
            - WORLD!

    "YAML::Active::lc"
        Like "YAML::Active::uc", but lowercases the values.

WRITING YOUR OWN PLUGIN
    Suppose you want to write an activation plugin that takes a reference to
    an array of numbers and adds them.

    By including the string "YAML::Active" in the package name we can let
    "YAML::Active" load the package when necessary. All we need to do is to
    provide a "yaml_activate()" method that does the work.

      package My::YAML::Active::Add;

      use YAML::Active qw/array_activate assert_arrayref/;

      sub yaml_activate {
          my $self = shift;
          assert_arrayref($self);
          my $result;
          $result += $_ for @{ array_activate($self) };
          return $result;
      }

    Now you can do:

      result: /My::YAML::Active::Add
        - 1
        - 2
        - 3
        - 7
        - 15

    And the result would be:

      result: 28

    This could be the beginning of a YAML-based stack machine or at least an
    RPN calculator...

INSTALLATION
    See perlmodinstall for information and options on installing Perl
    modules.

BUGS AND LIMITATIONS
    No bugs have been reported.

    Please report any bugs or feature requests through the web interface at
    <http://rt.cpan.org/Public/Dist/Display.html?Name=YAML-Active>.

AVAILABILITY
    The latest version of this module is available from the Comprehensive
    Perl Archive Network (CPAN). Visit <http://www.perl.com/CPAN/> to find a
    CPAN site near you, or see <http://search.cpan.org/dist/YAML-Active/>.

    The development version lives at
    <http://github.com/hanekomu/YAML-Active/>. Instead of sending patches,
    please fork this project using the standard git and github
    infrastructure.

AUTHOR
      Marcel Gruenauer <marcel@cpan.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2003 by Marcel Gruenauer.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

