NAME
    dTemplate - A powerful template handling logic with advanced features.

SYNOPSIS
      use dTemplate;

      $mail_template = define dTemplate "mail_tmpl.txt";# definition

      $mail = $mail_template->parse(                    # parsing
        TO      => "foo@bar.com",
        SUBJECT => $subject,
        BODY    => 
          sub { $email_type==3 ? $body_for_type_3 : $body_for_others },
        SIGNATURE=> $signature_template->parse( KEY => "value" )
      );

      print "Please send this mail: $mail";

      where mail_tmpl.txt is:

        From    : Me
        To      : $TO$
        Subject : $SUBJECT$

        Message body:
        $BODY$

        $SIGNATURE$

      # Advanced feature: Styling

      $style={lang =>'hungarian',color=>'white'};     # Style definition

      $html_template = choose dTemplate( $style,      # Selector definition
        'hungarian+white' => 
                define dTemplate("hun_white_template.html"),
        'spanish'         => 
                define dTemplate("spanish.html"),
        'black+hungarian' => 
                define dTemplate("hun_black_template.html"),
        'english'         => 
                define dTemplate("english_template.html"),
        'empty'           => 
          "<html>This is a text, $BODY$ is NOT substituted!!!!"</html>",
        ''                => 
                text dTemplate "<html>$BODY$</html>",  # default
      );

      $body_template= choose dTemplate( $style,       # Selector definition
        'hungarian'       => 
                define dTemplate("sziasztok_emberek.html"),
        'spanish'         => 
                define dTemplate("adios_amigos.html"),
        ''                => 
                define dTemplate("bye_bye.html"),
      );

      print $html_template->parse(BODY => $body_template->parse());
        # will print "sziasztok_emberek.html" in the
        #"hun_white_template.html"

      %$style=();
      print $html_template->parse(BODY => $body_template->parse());
        # will print "bye_bye.html" surrounded by "<html>" and "</html>" tags.

      %$style=( lang => 'english' );
      print $html_template->parse(BODY => $body_template->parse());
        # will print the "bye_bye.html" in of the "english_template.html"

DESCRIPTION
    This module is aimed to be a simple, general-purpose, lightweight, but
    very powerful templating system.

    You can write template-parsing routines in the way the templates are
    structured logically. Starting from the biggest to the smallest. Your
    program code will be very clear, structured and easy to understand. This
    logic can be attained by using inline subroutines as values of template
    variables. (Look at the example at the end of the document)

USAGE
    First, you need to know how a template looks like, then you need to know
    how to define a template in a perl program, then you can parse it.

    After that you can see how to make new encoders.

  How a template looks like

    A template is a simple text file, which contains template variable
    placeholders.

    The full format of a placeholder is:

      $Template_Variable%printf_style_format_string*encoder1*encoder2$

    Where:

    Template_Variable
        It is a mandatory part of the placeholder. Can contain any
        (locale-aware) alphanumeric characters and '.' .

    %printf_style_format_string
        This is an optional part. Used when you want to format the output.
        You can use as many '%' as you want, it can be good to pad the
        variable, for example when you parse a table. E.g: $MONEY%%%%%%011d$
        is a valid placeholder.

    *encoder
        There are predefined encoders in the module, which can be used to
        format the input data. These are:

          - u    : url-encoder
          - h    : HTML-encoder (converts > to &gt;, etc)
          - uc   : convert the string to uppercase
          - lc   : convert the string to lowercase

        You can use zero or more of these:

          $TITLE*uc*h$

        Read more on encoders (and how to make new encoders) in the Encoders
        part.

  Definition of a template

    There are 3 ways to define a template.

    $template = define dTemplate $filename
        This reads the template from a file.

    $template = text dTemplate $scalar
        This creates a template from a scalar

    $template = choose dTemplate $hash, "style1" => $template1, "style2" =>
    ...
        It is the definition of the template chooser. It is the way how you
        can create styled templates.

  Parsing

    Parsing means substituting the variables which are defined in the
    template. It can be done by simply calling the "parse" method of a
    dTemplate object.

    The parameters of the "parse" method are the substitution definitions.

    You can provide substitution parameters in two form:

      - list of name => value pairs
      - with a hash reference

    You can mix them if you want:

      $template->parse(
        name => $value,
        { name2 => $value2, name3 => $value3 },
        name4 => $value4,
        { name5 => $value5 },
        ...
      )

    The "value" can be:

    scalar or scalar ref.
        If a value is scalar, it will be substituted. Scalar refs can be
        used to save some memory if you use them more than one time.

    code reference ( sub { }, or \&subroutine )
        The sub will be evaluated at each occurence of the template
        variable.

    hash
        You can assign a hash to a template variable if you want. In this
        way, you can use structured data in the templates, e.g you assign a
        { name => "Greg", "zip" => 111 } to the template variable "person",
        and if you use "person.name" in the template, you will get "Greg"
        back. Nesting (more "."-s) will also work.

    You can use %dTemplate::parse hash to assign global parse parameters.

    The return value of the parse method is a dTemplate::Scalar object,
    which can be used as a simple scalar, but really it is a scalar
    reference to save some memory. It is useful if you use large templates.

  Encoders

    The global hash, %dTemplate::ENCODERS contains the defined encoders.

    The hash keys are the names, the values are subroutine references. These
    subs get the encodable data as the first parameter and returns the
    encoded value.

  $dTemplate::parse{''}

    $dTemplate::parse{''} is a special hash key in the %dTemplate::parse
    hash. This value is parsed into the place of the unassigned variable.

    By default, it is an empty scalar, so you won't even notice if you
    forget to assign a variable.

    If you want to be warned if a variable is not assigned, you can use the
    following code reference:

      use Carp qw(cluck);
      $dTemplate::parse{''} = sub {
          cluck "$_[0] is not assigned";
          return "";
      }

    By this, the output of the further "parse" calls will call this sub if a
    variable is not assigned.

  Magical (tied) hashes

    You can use magical hashes everywhere in the "parse" method parameter
    list, where you can to use normal hashes, but because I redesign the
    "parse" method with the speed with the first priority, it works quite a
    bit different than the older ( <= 2.0 ) versions.

    At template-compile time, the "compile" method collects the variable
    names, which are found in that template, and the "parse" method knows
    which variables are required for processing this template.

    When the "parse" method realizes that the given parameter is a hash
    reference, then it always tries all the remaining template variables
    (which are not assigned in the preceding part of the parameter list) in
    that hash reference.

    Imagine the following situation:

      $template->parse( name => "blow", \%hash);

    ... where %hash is a magical hash, and the $template contains the
    "name", "address" and "method.type" variables. When the parse method
    meets with the \%hash, the "name" is already assigned, so it olny tries
    to read the $hash{address} and $hash{method} variables.

    This is not a problem with normal hashes, but if you use magical hashes,
    you may have a very expensive FETCH function, and this effect can cause
    problems.

    There are two way to work around it:

    *   Use qualified variable names. If you use the following form of
        parse:

          $template->parse( name => "blow", data => \%hash);

        ... then the %hash is called only when the template parser finds the
        "data.address" and "data.method.type" variable references in the
        template. Of course, you have to change the template variable names
        also.

    *   Use the hash instead of a hash reference:

          $template->parse( name => "blow", %hash);

        In this case, the magical hash is iterated through when the
        parameter list is assembled. This is better only if you are afraid
        of random key retrieval, but it can be also slow, if the FIRSTKEY,
        NEXTKEY and FETCH operations are slow.

        But if the random-key retrieval is not a problem for your magical
        hash, then use the default form instead of this, because that
        requires less operation (only one FETCH).

HINTS
    *   In the first parse of every template, the templates will be
        compiled. It is used to speed up parsing.

    *   Don't forget that %dTemplate::parse can be localized. This means you
        can define local-only variable assignments in a subroutine:

          local %dTemplate::parse=( 
            %dTemplate::parse, 
            local_name => $value 
          );

    *   You don't need to use text as the input value of an encoder, you can
        use any scalar, even referenes! If you want (for example) print a
        date by a date encoder, which expects the date to be an array ref of
        [ year, month, day ], then you can do this, e.g:

           $dTemplate::ENCODERS{date}=sub {
             return "" if ref($_[0]) ne 'ARRAY';
             return $_[0]->[0]."-".$_[0]->[1]."-".$_[0]->[2];
           }

        Then, when you put $START_DATE*date$ to a template, you can parse
        this template:

          $template->parse(
            START_DATE => [2000,11,13],
            ...
          );

ALL-IN-ONE EXAMPLE
    It is an example, which contains most of the features this module has.
    It is not intended to be a real-world example, but it can show the usage
    of this module.

    This example consists of one program, and some template modules.

    The executable version of this program can be found in the example
    directory of the module distribution.

      use dTemplate;

      ### definition of the standard templates

      my @TEMPLATE_LIST=qw(page table_row table_cell);
      my $templates={};
      foreach my $template (@TEMPLATE_LIST) {
        $templates->{$template} = 
          define dTemplate("templates/$template.htm");
      }

      ### definition of the styled templates (styles = languages)

      my @STYLES=qw(eng hun);
      my @STYLED_TEMPLATE_LIST=qw(table_title);

      my $style_select={ lang => 'hun' }; 

      foreach my $template (@STYLED_TEMPLATE_LIST) {
        my @array=();
        foreach my $style (@STYLES) {
          push @array, $style => 
            define dTemplate("text/$style/$template.txt");
        }
        $templates->{$template} = 
          choose dTemplate $style_select, @array;
      }

      ### setting up input data

      my $table_to_print=[
        [ "Buwam",   3, 6, 9 ],
        [ "Greg",    8, 4, 2 ],
        [ "You're",  8, 3, 4 ],
        [ "HTML chars: <>", 3],
      ];

      ### setting up the global parse hash with parse parameters;

      $dTemplate::parse{PAGENO}=7;

      ### settings up a hash with personal data.

      my $person_hash={
        name => { first_name => "Greg" },
        zip  => "9971",
      };

      ### this hash is simply added to other parse parameters

      my $parse_hash={
        "unknown" => { data => 157 },
      };

      ### the main page parse routine

      print $templates->{page}->parse(
        TABLE_TITLE =>             # name => value pair
          $templates->{table_title}->parse(),
        TABLE => sub {             # name => value pair. value is a sub
          my $ret="";
          foreach my $row (@$table_to_print) {
            $ret .= $templates->{table_row}->parse(
              BODY => sub {
                my $ret="";
                foreach my $cell (@$row) {
                  $ret .= $templates->{table_cell}->parse(
                    TEXT => $cell,
                  )
                }
                return $ret;
              }
            )
          }
          return $ret;
        },
        "person" => $person_hash,  # name => value pair. value is a href
        $parse_hash,               # only a hash with parse parameters
      );

    And the templates:

    templates/page.htm:
          <html>
          <body>

          <h1>$TABLE_TITLE*h$</h1>

          <table>
          $TABLE$
          </table>

          <br>
          Person name: $person.name*h$, zip code: $person.zip*h$
          <br>

          Unknown data: $unknown.data*h$
          <br>

          Page: $PAGENO%02d*h$

          </body>
          </html>

    templates/table_row.htm:
          <tr>$BODY$</tr>

    templates/table_cell.htm:
          <td>$TEXT*h$</td>

    text/eng/table_title.txt:
          Table 1

    text/hun/table_title.txt:
          1. táblázat

COPYRIGHT
    Copyrigh (c) 2000-2001 Szabó, Balázs (dLux)

    All rights reserved. This program is free software; you can redistribute
    it and/or modify it under the same terms as Perl itself.

AUTHOR
    dLux (Szabó, Balázs) <dlux@kapu.hu>

SEE ALSO
    perl(1), HTML::Template, Text::Template, CGI::FastTemplate, Template.

