MML

Author: Michael Olney <michael@spectralforms.com>
Version: 0.3
Status: Unstable

MML is a markup language intended to provide a better way to specify HTML documents. The main advantages are a simplified syntax and a template system that makes it easier to achieve abstraction when specifying document contents. The following table shows the relation between the syntax of MML and HTML:

HTML	MML
<br/>	{br}
<em></em>	{em->}
<a href=cat>meow</a>	{a{href->cat}->meow}
two&nbsp;&nbsp;spaces	two~~spaces

Unlike HTML, whitespace reduction within a tag body is part of the syntax, though the renderer is free to reduce the emitted whitespace further.

C-style comments ('/* */') are available. Characters are escaped either by preceding them with a backslash ('') or surrounding them with backticks ('`'). Literal characters are passed on as literal to HTML, but no attempt is made to prevent the renderer from doing things like collapsing whitespace. However, the syntax is designed to deal with these issues at the syntax level so that users don't usually have to worry about HTML's whitespace rules.

An important distiction between MML and HTML is that MML attribute values can contain the document structures (tags, text etc) that are allowed inside tag bodies. HTML allows only strings. This is important for the custom tag system.

MML is inspired partly by Erik Naggum's unreleased Enamel (NML) markup language.

Abstracting Markup With Custom Tags

MML also supports the creation of custom tags through a template syntax. Tags are defined by placing MML files (with the extension .mtag) into the path of the MML processor containing tags with names beginning with $ inside them. These special tags are treated as variables; when the tag is included in an MML file the attributes in the specific instance of the tag are substituted into the variables in the .mtag file. For example, a template might be created by placing the following into a file called field-entry.mtag

{div{class->field-entry}->
    {label{for->{$name}}->{$friendly-name}}
    {input{type->text}{name->{$name}}}
}

This template could then be invoked with the following syntax:

{@field-entry{name->first_name}{friendly-name->First Name}}

The substitution performed is syntactic and the results are guaranteed to be valid MML. Using this mechanism it is possible to abstract away some of your HTML tags in order to achieve a more semantic style of markup, e.g.:

{@band-list{name->The Beatles}{members->
    {@band-member{name->John Lennon}{portrait->john.jpg}}
    {@band-member{name->Paul McCartney}{portrait->paul.jpg}}
    {@band-member{name->Ringo Starr}{portrait->ringo.jpg}}
    {@band-member{name->George Harrison}{portrait->george.jpg}}
}

In programming terms, you can think of a custom tag as a function that takes in some arguments and returns document structure. Under this analogy, the attributes are named arguments and the child elements are the the positional arguments.

Future Work

So far MML is just a system I designed to build my personal website with. A more complete tool would need lots of extra features, including:

• Control structures and other programming constructs for defining custom tags.
• Encapsulation of CSS such that selectors cannot be used to cross abstraction boundaries.
• Custom CSS attributes, so that client CSS can usefully customize any custom elements.
• A module system. It would be useful to organise tags into modules that can be imported and reused.
• Encapsulation of DOM elements and other JavaScript structures.

Running

To install the package, use stack:

$ stack install

To convert an MML file to HTML, run the mml command:

$ mml --infile=index.mml --infmt=mml --outfile=index.html --outfmt=html