NAME

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

VERSION

       version 0.81

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
       DateTime::Format::Builder.

       •   on_match

       •   on_fail

       •   postprocess

       •   preprocess

       •   label

       •   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

       See DateTime::Format::Builder for details.

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.

AUTHORS

       •   Dave Rolsky <autarch@urth.org>

       •   Iain Truskett

COPYRIGHT AND LICENSE

       This software is Copyright (c) 2013 by Dave Rolsky.

       This is free software, licensed under:

         The Artistic License 2.0 (GPL Compatible)