NAME
YAML::Active - Combine data and logic in YAML
SYNOPSIS
use YAML::Active;
my $data = Load(<<'EOYAML');
pid: !perl/YAML::Active::PID
doit:
foo: bar
include_test: !perl/YAML::Active::Include
filename: t/testperson.yaml
ticket_no: !perl/YAML::Active::Concat
- '20010101.1234'
- !perl/YAML::Active::PID
doit:
- !perl/YAML::Active::Eval
code: sub { sprintf "%04d", ++(our $cnt) }
setup:
1: !perl/Registry::YAML::Active::WritePerson
person:
personname: Foobar
nichdl: AB123456-NICAT
2: !perl/Registry::YAML::Active::WritePerson
person: !perl/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: !perl/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 !perl/YAML::Active::Concat
- foo
- !perl/YAML::Active::PID
doit:
- !perl/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".
EXPORT
Nothing is exported by default, but you can request each of the
following 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.
"Load()"
Like "YAML"'s "Load()", but activates the data structure after
loading it and returns the activated data structure.
"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".
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:
- !perl/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: !perl/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: !perl/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: !perl/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
- !perl/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: !perl/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: !perl/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...
BUGS
If you find any bugs or oddities, please do inform the author.
INSTALLATION
See perlmodinstall for information and options on installing Perl
modules.
AVAILABILITY
The latest version of this module is available from the Comprehensive
Perl Archive Network (CPAN). Visit to find a
CPAN site near you. Or see
.
VERSION
This document describes version 1.00 of "YAML::Active".
AUTHOR
Marcel Grünauer
COPYRIGHT
Copyright 2001-2003 Marcel Grünauer. All rights reserved.
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.