/ 
DSL-HTML-0.006
River stage zero No dependents
/ DSL::HTML

NAME

DSL::HTML - Declarative DSL(domain specific language) for writing HTML templates within perl.

DESCRIPTION

Templating systems suck. This sucks less.

In most cases a templating system lets you write html files with embedded logic. The embedded logic can be a template specific language, or it can let you embed code from the projects programming language.

An alternative that has been played with is constructing the HTML directly in your application language. In most cases this sucks more. OOP, where objects are built and then associated via method calls is NOT a friendly way to build a complex tree.

DSL::HTML takes the alternative approach, but does it in a significantly more elegent way. Instead of forcing you to construct objects and build a tree manually via methods, you define the tree via nested subroutines. This is sort of a functional approach to tree building.

EARLY VERSION WARNING

THIS IS AN EARLY VERSION! Basically I have not decided 100% that the API will remain as-is (though it likely will not change much). I am also embarrased to admit that this code is very poorly tested (Yes, this is more embarrasing considering I wrote Fennec).

BENEFITS

The template language is perl

There is no embedded template language, your logic is all in perl, you treat all tags like perl objects. The nested block syntax allows this while also saving you from the PITA of direct object manipulation; that is you do not need to say $tag->insert(Tag->new) or similar.

No need to hand-write html

Hand-written HTML is easy to screw up. You might forget to close a tag, or nest things improperly. The nature of browsers it to try to make it work anyway, so you can sometimes spend hours debugging broken html.

Syntax checking is done by perl

The nested-blok syntax is checked by perl. If you make a syntax error, or a typo, perl will typically catch your mistake when you try to build the package.

Templates and tags are built like subroutines

This means you call your template with argumnets similar to how you can any function with arguments.

Templates can be imported/exported between modules.

You can create perl modules that are simply template libraries, other modules can load these libraries to gain access to the templates.

SYNOPSYS

# Note: This brings in an import() method.
# See the EXPORTS - import() section later in this doc for more info.
use DSL::HTML;

template my_template {
    my @options = @_;

    # The lexical variable '$tag' is defined for you automatically and is a
    # reference to the current tag on the stack (usually <body>)
    $tag->attr( foo => 'bar' );

    css 'my/css/file.css'; # Goes to the header

    tag h1 { "Welcome!" }

    tag h2 { "Choices:" }

    # Tags nest naturally, here is a <ul> with nested <li>s
    # Tags can be nested to any depth.
    tag ul {
        my $n = 1;
        for my $option (@options) {
            my $zebra = $n++ % 2 ? 'odd' : 'even';

            tag li(class => $zebra) { $option }
        }
    }

    # Include another template, with arguments if desired.
    include some_other_template => ( ... );

    tag div(class => 'footer') {
        # the lexical $tag is defined for you, and is the tag currently
        # being built.
        $tag->attr( foo => 'bar' );
        tag span { 'copyright &copy;' }
        text "foobar incorperated";
    }
}

my $html1 = build_template my_template => qw/foo bar baz/;
my $html2 = build_template my_template => qw/bat ban boo/;

Note: Any source file that uses the package defined above would automatically gain all the templates defined within, as well as the 'build_template' function.

GUTS

This package works via a stack system. When you build a template a rendering object is pushed onto a stack, the codeblock you provided is then executed. Any tags defined at this point get added to the rendering object at the top of the stack.

When a tag is defined it is pushed to the top of the stack, then the codeblock for it is run. In this way you can create a nested HTML structure. After all the nested codeblocks are executed, the html content is built from the object tree.

Because of this stack system you can also write helper objects or functions which themselves call tag, or any other export provided by this package, so long as those helpers are called (no matter how indirectly) from within a template codeblock you are fine.

CONVERTING EXISTING HTML INTO TEMPLATES

DSL::HTML::Compiler can be used to convert existing HTML into DSL::HTML templates.

STANDARD TEMPLATE LIBRARY

DSL::HTML::STL is a library of templates available to use.

EXPORTS

import()

When you use DSL::HTML it will inject a method called import into your package. This is done so that anyone that loads your package via use will gain all your templates, as well as the build_template function.

Note: This will cause a conflict if you use it in any module that uses Exporter, Exporter::Declare, or similar exporter modules. To prevent this you can tell DSL::HTML not to inject import() at use time, either by rejecting it specifically, or by specifying with functions you do want:

Outright rejection:

use DSL::HTML qw/-default !import/;

Just what you want:

use DSL::HTML qw/template tag css js build_template get_template include/;

If you do either of these then loading your template package will NOT make your templates available to the package loading it, but you can get them via:

use Your::Package();
my $tmp = Your::Package->get_template('the_template');
my $html = $tmp->compile( ... );
template NAME(%PARAMS) { ... }
template NAME { ... }
$t = template NAME(%PARAMS) { ... }
$t = template NAME { ... }

Define a template. If the return value is ignored the template will be inserted into the current package metadata. If you capture the return value then nothing is stored in the meta-data.

Parameters are optional, currently the only used parameter is 'indent' which can be set to any string, but you probably want "\t" or " ".

Note: the lexical variable $tag is defined for you, and contains the tag currently being built. In most cases this is the body tag, however when you include '...' a template the tag will be whatever tag the template is included into.

An DSL::HTML::Template object is created.

tag NAME(%ATTRIBUTES) { ... }
tag NAME { ... }
tag NAME { "simple text" }

Define a tag. Never returns anything. All attributes are optional, any may be specified.

Note: the lexical variable $tag is defined for you. This variable contains the tag being built (the one your block is defining.)

Calls to tag must be made within a template, they will not work anywhere else (though because of the stack you may call tag() within a function or method that you call within a template).

If the codeblock does not add any text or tag elements to the tag, and you return a simple string from the codelbock, the string will be added as a text element. This allows for shortcutting tags that only contain basic text.

Note: the 'head', 'body' and 'html' tags have special handling. Every time you call tag head {...} within a template you get the same tag object. The same behavior applies to the body tag.

You can and should nest calls to tag, this allows you to create a tag tree.

template foo {
    tag parent {
        tag child {
            ...
        }
    }
}

Under the hood an HTML::Element is created for each tag.

text "...";

Define a text element in the current template/tag.

Under the hood an HTML::Element is created.

css "path/to/file.css";

Append a css file to the header. This can be called multiple times, each path will only be included once.

js "path/to/file.js";

Append a js file to the end of the <html> tag. This can be called multiple times, each path will only be included once.

attr name => 'val', ...;
attr { name => 'val' };

Set specific attributes in the current tag. Arguments may be hashref or key/value list.

add_class 'name';

Add a class to the current tag.

del_class 'name';

Remove a class from the current tag.

$html = build_template $TEMPLATE => @ARGS
$html = build_template $TEMPLATE, @ARGS
$html = build_template $TEMPLATE

Build html from a template given specific arguments (optional). Template may be a template name which will can be found in the current package meta-data, or it can be an DSL::HTML::Template object.

include $TEMPLATE => @ARGS
include $TEMPLATE, @ARGS
include $TEMPLATE

Nest the result of building another template within the current one.

$tmp = get_template($name)
$tmp = PACKAGE->get_template($name)
$tmp = $INSTANCE->get_template($name)

Get a template. When used as a function it will find the template in the current package meta-data. When called as a method on a class or instance it will find the template in the metadata for that package.

WHOAH! NICE SYNTAX

The syntax is provided via Exporter::Declare which uses Devel::Declare.

EXAMPLES

TEMPLATE PACKAGE

package My::Templates;
use strict;
use warnings;

use DSL::HTML;

template ulist {
    # DSL::HTML::Rendering.
    my @items = @_;

    css 'ulist.css';

    tag ul(class => 'my_ulist') {
        for my $item (@items) {
            tag li { $item }
        }
    }
}

template list_pair {
    my ($items_a, $items_b) = @_;
    include ulist => @$items_a; # Using the ulist template above
    include ulist => @$items_b; # " "
}

1;

Now to use it:

# This will import the 'build_template' function, as well as all the
# templates defined by the package. You can request only specific templates
# by passing them as arguments to the use statement.
use My::Templates;

my $html = build_template list_pair => (
    [qw/red green blue/],
    [qw/one two three/],
);

print $html;

Should give us:

<html>
    <head>
        <link type="text/css" rel="stylesheet" href="ulist.css" />
    </head>

    <body>
        <ul class="my_ulist">
            <li>
                red
            </li>
            <li>
                green
            </li>
            <li>
                blue
            </li>
        </ul>
        <ul class="my_ulist">
            <li>
                one
            </li>
            <li>
                two
            </li>
            <li>
                three
            </li>
        </ul>
    </body>
</html>

TEMPLATE OBJECT

If you do not like defining templates as package meta-data you can use them in a less-meta form:

use strict;
use warnings;

use DSL::HTML;

my $ulist = template ulist {
    # DSL::HTML::Rendering.
    my @items = @_;

    css 'ulist.css';

    tag ul(class => 'my_ulist') {
        for my $item (@items) {
            tag li { $item }
        }
    }
}

my $list_pair = template list_pair {
    my ($items_a, $items_b) = @_;
    $ulist->include( @$items_a ); # Using the ulist template above
    $ulist->include( @$items_b ); # " "

    # Alternatively you could do:
    # include $ulist => ...;
    # the 'include' keyword works with at emplate object as an argument
}

my $html = $list_pair->compile(
    [qw/red green blue/],
    [qw/one two three/],
);

# You could also do:
# build_template $list_pair => (...);

print $html;

Should give us:

<html>
    <head>
        <link type="text/css" rel="stylesheet" href="ulist.css" />
    </head>

    <body>
        <ul class="my_ulist">
            <li>
                red
            </li>
            <li>
                green
            </li>
            <li>
                blue
            </li>
        </ul>
        <ul class="my_ulist">
            <li>
                one
            </li>
            <li>
                two
            </li>
            <li>
                three
            </li>
        </ul>
    </body>
</html>

SEE ALSO

HTML::Declare

HTML::Declare seems to be a similar idea, but I dislike the feel of it. That said still have to give the author props for doing it as good as possible without Devel::Declare.

AUTHORS

Chad Granum exodist7@gmail.com

COPYRIGHT

Copyright (C) 2013 Chad Granum

DSL-HTML is free software; Standard perl license (GPL and Artistic).

DSL-HTML is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the license for more details.