use warnings;
use strict;

sub escape_ents {
  local $_ = shift;
  s/&/&/g;
  s/</&lt;/g;
  s/>/&gt;/g;
  s/"/&quot;/g; # "
  s/'/&apos;/g;
  return $_;
}

sub stringify_attribs {
  return join '',
    map{
      ' '.escape_ents( $_ ).'="'.escape_ents( $_[0]{$_} ).'"'
    } sort keys %{$_[0]};
}

##</code><code>##


sub XML_elem {
  my $tag = shift;
  my @results; # return value

  my $attribs = shift @_ if( ref( $_[0] ) eq 'HASH' );

  push @results, "<${tag}" . stringify_attribs( $attribs ) . ">";

  if( @_ == 0 ) { # handle an empty element
    $results[0] =~ s|>$| />|;
    return @results;
  }

  foreach my $arg ( @_ ) {
    if( ref( $arg ) eq 'CODE' ) {
      push @results, map{ "  $_" } $arg->(); # <--- ???
    } else {
      push @results, '  ' . escape_ents( $arg )
    }
  }

  push @results, "<\\${tag}>";
  return @results;
}

##</code><code>##


print "\n == code fragment 1 ============================================= \n";

print join "\n",
  XML_elem( 'root', { ID => 0 },
    XML_elem( 'branch',
      XML_elem( 'sub_branch', { foo => 2 },
        'some contents & entities, "<>"'
      ),
      'other contents',
    ),
  'root stuff',
  );


##</code><code>##

__END__

# ml (Make Lazy) takes a reference to a subroutine as it's 1st arg.  All
# remaining args are saved and used as arguments for the subroutine when
# the results of execution are desired.  returns a subroutine that behaves
# almost exactly as if the subroutine had been called when ml was called.
sub ml {
  my $sub = shift;
  my @args = @_;
  return sub {
    return $sub->( @args );
  };
}


##</code><code>##


print "\n == code fragment 2 ============================================= \n";

print join "\n",
  XML_elem( 'root', { ID => 0 },
    ml( \&XML_elem, 'branch',
      ml( \&XML_elem, 'sub_branch', { foo => 2 },
        'some contents & entities, "<>"'
      ),
      'other contents',
    ),
  'root stuff',
  );


##</code><code>##

__END__

# ca4ml (Curry Arguments for ML)
sub ca4ml {
  my $sub = shift;
  my $tag = shift;
  return sub {
    my @args = @_;
    return ml( $sub, $tag, @args );
  }
}

print "\n == code fragment 3 ============================================= \n";

my $root       = ca4ml( \&XML_elem, 'root' );
my $branch     = ca4ml( \&XML_elem, 'branch' );
my $sub_branch = ca4ml( \&XML_elem, 'sub_branch' );

print join "\n",
  $root->( { ID => 0 },
    $branch->(
      $sub_branch->( { foo => 2 },
      	 'some contents & entities "<>"'
      ),
      'other contents',
    ),
    'root stuff',
  )->();


##</code><code>##

__END__

sub make_func {
  my $tag = shift;
  return sub {
    my @args = @_;
    return ml( \&XML_elem, $tag, @args );
  }
}

print "\n == code fragment 4 ============================================= \n";

$root       = make_func( 'root' );
$branch     = make_func( 'branch' );
$sub_branch = make_func( 'sub_branch' );

print join "\n",
  $root->( { ID => 0 },
    $branch->(
      $sub_branch->( { foo => 2 },
	 'some contents & entities "<>"'
      ),
      'other contents',
    ),
    'root stuff',
  )->();

;
__END__