Title

# html { # head { title { text "Title" } }; # body { # p { class_ "warning"; text "paragraph" } # }; # } ##

##

# doc {
#     my_elem {
#         # children go here
#     };
# };

##

##

# my_elem {
#     text "some text";
#     my_attr_ "value";
# };

##

##

our $__frag;  # points to fragment under active construction

sub doc(&) {
    my ($content_fn) = @_;
    local $__frag = [undef,undef,undef];
    $content_fn->();
    $__frag->[2][0];
}

sub _elem {
    my ($elem_name, $content_fn) = @_;
    # an element is represented by the triple [name, attrs, children]
    my $elem = [$elem_name, undef, undef];
    do { local $__frag = $elem; $content_fn->() };
    push @{$__frag->[2]}, $elem;
}

sub _attr {
    my ($attr_name, $val) = @_;
    push @{$__frag->[1]}, [$attr_name, $val];
}

sub text($) {
    push @{$__frag->[2]}, @_;
}

##

##

sub define_vocabulary {
    my ($elems, $attrs) = @_;
    eval "sub $_(&) { _elem('$_',\@_) }"     for @$elems;
    eval "sub ${_}_(\$) { _attr('$_',\@_) }" for @$attrs;
}

##

##

BEGIN {
    define_vocabulary(
        [qw( html head title body h1 h2 h3 p img br )],
        [qw( src href class style )]
    );
}

##

##

my $my_doc = doc {
    html {
        head { title { text "Title" } };
        body {
            p { class_ "warning"; text "paragraph" }
        };
    }
};

use Data::Dumper;
$Data::Dumper::Indent = $Data::Dumper::Terse = 1;
print Dumper $my_doc;
# [
#   'html',
#   undef,
#   [
#     [
#       'head',
#       undef,
#       [
#         [
#           'title',
#           undef,
#           [
#             'Title'
#           ]
#         ]
#       ]
#     ],
#     [
#       'body',
#       undef,
#       [
#         [
#           'p',
#           [
#             [
#               'class',
#               'warning'
#             ]
#           ],
#           [
#             'paragraph'
#           ]
#         ]
#       ]
#     ]
#   ]
# ]

##

##

use XML::Writer;

sub render_via_xml_writer {
    my $doc = shift;
    my $writer = XML::Writer->new(@_);  # extra args go to ->new()
    my $render_fn;
    $render_fn = sub {
        my $frag = shift;
        my ($elem, $attrs, $children) = @$frag;
        $writer->startTag( $elem, map {@$_} @$attrs );
        for (@$children) {
            ref() ? $render_fn->($_) : $writer->characters($_);
        }
        $writer->endTag($elem);
    };
    $render_fn->($doc);
    $writer->end();
}

##

##

render_via_xml_writer( $my_doc, DATA_MODE => 1, UNSAFE => 1 );
# 
# 
# Title
# 
# 
# paragraph
# 
# 

##

##

sub render_doc(&) {
    my $docfn = shift;
    render_via_xml_writer(
        doc( \&$docfn ),
        DATA_MODE => 1,
        UNSAFE => 1
    );
}

##

##

render_doc {
    html {
        head { 
            title { text "My grand document!" }
        };
        body {
            h1 { text "Heading" };
            p {
                class_ "first";       # attribute class="first"
                text "This is the first paragraph!";
                style_ "font: bold";  # another attr
            };
            # it's just Perl, so we can mix in other code
            for (2..5) {
                p { text "Plus paragraph number $_." }
            }
        };
    };
};
# 
# 
# My grand document!
# 
# 
# Heading
# This is the first paragraph!
# Plus paragraph number 2.
# Plus paragraph number 3.
# Plus paragraph number 4.
# Plus paragraph number 5.
# 
#