DateTime::Format::Builder::Parser(3pm)			User Contributed Perl Documentation		    DateTime::Format::Builder::Parser(3pm)

NAME

       DateTime::Format::Builder::Parser - Parser creation

SYNOPSIS

	   my $class = 'DateTime::Format::Builder::Parser';
	   my $parser = $class->create_single_parser( %specs );

DESCRIPTION

       This is a utility class for DateTime::Format::Builder that handles creation of parsers. It is to here that "Builder" delegates most of its
       responsibilities.

CONSTRUCTORS

METHODS

       There are two sorts of methods in this class. Those used by parser implementations and those used by "Builder". It is generally unlikely
       the user will want to use any of them.

       They are presented, grouped according to use.

   Parameter Handling (implementations)
       These methods allow implementations to have validation of their arguments in a standard manner and due to "Parser"'s impelementation, these
       methods also allow "Parser" to determine which implementation to use.

       Common parameters

       These parameters appear for all parser implementations.	These are primarily documented in the main docs.

       o   on_match

       o   on_fail

       o   postprocess

       o   preprocess

       o   label

       o   length may be a number or an arrayref of numbers indicating the length of the input. This lets us optimise in the case of static length
	   input. If supplying an arrayref of numbers, please keep the number of numbers to a minimum.

       params

	   my $params = $self->params();
	   validate( @_, $params );

       Returns declared parameters and "common" parameters in a hashref suitable for handing to Params::Validate's "validate" function.

       params_all

	   my $all_params = $self->params_all();

       Returns a hash of all the valid options. Not recommended for general use.

       valid_params

	   __PACKAGE__->valid_params( %params );

       Arguments are as per Params::Validate's "validate" function.  This method is used to declare what your valid arguments are in a parser
       specification.

       whose_params

	   my $class = whose_params( $key );

       Internal function which merely returns to which class a parameter is unique. If not unique, returns "undef".

   Organising and Creating Parsers
       create_single_parser

       This takes a single specification and returns a coderef that is a parser that suits that specification. This is the end of the line for all
       the parser creation methods. It delegates no further.

       If a coderef is specified, then that coderef is immediately returned (it is assumed to be appropriate).

       The single specification (if not a coderef) can be either a hashref or a hash. The keys and values must be as per the specification.

       It is here that any arrays of callbacks are unified. It is also here that any parser implementations are used. With the spec that's given,
       the keys are looked at and whichever module is the first to have a unique key in the spec is the one to whom the spec is given.

       Note: please declare a "valid_params" argument with an uppercase letter. For example, if you're writing
       "DateTime::Format::Builder::Parser::Fnord", declare a parameter called "Fnord". Similarly, "DTFBP::Strptime" should have "Strptime" and
       "DTFBP::Regex" should have "Regex". These latter two don't for backwards compatibility reasons.

       The returned parser will return either a "DateTime" object or "undef".

       merge_callbacks

       Produce either undef or a single coderef from either undef, an empty array, a single coderef or an array of coderefs

   create_multiple_parsers
       Given the options block (as made from "create_parser()") and a list of single parser specifications, this returns a coderef that returns
       either the resultant "DateTime" object or "undef".

       It first sorts the specifications using "sort_parsers()" and then creates the function based on what that returned.

   sort_parsers
       This takes the list of specifications and sorts them while turning the specifications into parsers. It returns two values: the first is a
       hashref containing all the length based parsers. The second is an array containing all the other parsers.

       If any of the specs are not code or hash references, then it will call "croak()".

       Code references are put directly into the 'other' array. Any hash references without length keys are run through "create_single_parser()"
       and the resultant parser is placed in the 'other' array.

       Hash references with length keys are run through "create_single_parser()", but the resultant parser is used as the value in the length
       hashref with the length being the key. If two or more parsers have the same length specified then an error is thrown.

   create_parser
       "create_class()" is mostly a wrapper around "create_parser()" that does loops and stuff and calls "create_parser()" to create the actual
       parsers.

       "create_parser()" takes the parser specifications (be they single specifications or multiple specifications) and returns an anonymous
       coderef that is suitable for use as a method. The coderef will call "croak()" in the event of being unable to parse the single string it
       expects as input.

       The simplest input is that of a single specification, presented just as a plain hash, not a hashref. This is passed directly to
       "create_single_parser()" with the return value from that being wrapped in a function that lets it "croak()" on failure, with that wrapper
       being returned.

       If the first argument to "create_parser()" is an arrayref, then that is taken to be an options block (as per the multiple parser
       specification documented earlier).

       Any further arguments should be either hashrefs or coderefs.  If the first argument after the optional arrayref is not a hashref or coderef
       then that argument and all remaining arguments are passed off to "create_single_parser()" directly. If the first argument is a hashref or
       coderef, then it and the remaining arguments are passed to "create_multiple_parsers()".

       The resultant coderef from calling either of the creation methods is then wrapped in a function that calls "croak()" in event of failure or
       the "DateTime" object in event of success.

FINDING IMPLEMENTATIONS

       "Parser" automatically loads any parser classes in @INC.

       To be loaded automatically, you must be a "DateTime::Format::Builder::Parser::XXX" module.

       To be invisible, and not loaded, start your class with a lower class letter. These are ignored.

WRITING A PARSER IMPLEMENTATION

   Naming your parser
       Create a module and name it in the form "DateTime::Format::Builder::Parser::XXX" where XXX is whatever you like, so long as it doesn't
       start with a lower case letter.

       Alternatively, call it something completely different if you don't mind the users explicitly loading your module.

       I'd recommend keeping within the "DateTime::Format::Builder" namespace though --- at the time of writing I've not given thought to what
       non-auto loaded ones should be called. Any ideas, please email me.

   Declaring specification arguments
       Call "<DateTime::Format::Builder::Parser-"valid_params()>> with "Params::Validate" style arguments. For example:

	  DateTime::Format::Builder::Parser->valid_params(
	      params => { type => ARRAYREF },
	      Regex  => { type => SCALARREF, callbacks => {
		 'is a regex' => sub { ref(shift) eq 'Regexp' }
	      }}
	  );

       Start one of the key names with a capital letter. Ideally that key should match the XXX from earlier. This will be used to help identify
       which module a parser specification should be given to.

       The key names on_match, on_fail, postprocess, preprocess, label and length are predefined. You are recommended to make use of them. You may
       ignore length as "sort_parsers" takes care of that.

   Define create_parser
       A class method of the name "create_parser" that does the following:

       Its arguments are as for a normal method (i.e. class as first argument).  The other arguments are the result from a call to
       "Params::Validate" according to your specification (the "valid_params" earlier), i.e. a hash of argument name and value.

       The return value should be a coderef that takes a date string as its first argument and returns either a "DateTime" object or "undef".

   Callbacks
       It is preferred that you support some callbacks to your parsers.  In particular, "preprocess", "on_match", "on_fail" and "postprocess". See
       the main Builder docs for the appropriate placing of calls to the callbacks.

SUPPORT

       Support for this module is provided via the datetime@perl.org email list. See http://lists.perl.org/ for more details.

       Alternatively, log them via the CPAN RT system via the web or email:

	   http://perl.dellah.org/rt/dtbuilder
	   bug-datetime-format-builder@rt.cpan.org

       This makes it much easier for me to track things and thus means your problem is less likely to be neglected.

THANKS

       See DateTime::Format::Builder.

LICENCE AND COPYRIGHT

       Copyright X Iain Truskett, 2003. All rights reserved.

       This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.000 or,
       at your option, any later version of Perl 5 you may have available.

       The full text of the licences can be found in the Artistic and COPYING files included with this module, or in perlartistic and perlgpl as
       supplied with Perl 5.8.1 and later.

AUTHOR

       Iain Truskett <spoon@cpan.org>

SEE ALSO

       "datetime@perl.org" mailing list.

       http://datetime.perl.org/

       perl, DateTime, DateTime::Format::Builder.

       Params::Validate.

       DateTime::Format::Builder::Parser::generic, DateTime::Format::Builder::Parser::Dispatch, DateTime::Format::Builder::Parser::Quick,
       DateTime::Format::Builder::Parser::Regex, DateTime::Format::Builder::Parser::Strptime.

perl v5.10.1							    2010-03-14				    DateTime::Format::Builder::Parser(3pm)