Haml and Sass
Haml and Sass are templating engines
for the two most common types of documents on the web:
HTML and CSS, respectively.
They are designed to make it both easier and more pleasant
to code HTML and CSS documents,
by eliminating redundancy,
reflecting the underlying structure that the document represents,
and providing elegant, easily understandable, and powerful syntax.
Using
Haml and Sass can be used from the command line
or as part of a Ruby web framework.
The first step is to install the gem:
gem install haml
After you convert some HTML to Haml or some CSS to Sass,
you can run
haml document.haml
sass style.scss
to compile them.
For more information on these commands, check out
haml –help
sass –help
To install Haml and Sass in Rails 2,
just add config.gem "haml" to config/environment.rb.
In Rails 3, add gem "haml" to your Gemfile instead.
and both Haml and Sass will be installed.
Views with the .html.haml extension will automatically use Haml.
Sass is a little more complicated;
.sass files should be placed in public/stylesheets/sass,
where they’ll be automatically compiled
to corresponding CSS files in public/stylesheets when needed
(the Sass template directory is customizable…
see the Sass reference for details).
For Merb, .html.haml views will work without any further modification.
To enable Sass, you also need to add a dependency.
To do so, just add
dependency “merb-haml”
to config/dependencies.rb (or config/init.rb in a flat/very flat Merb application).
Then it’ll work just like it does in Rails.
Sass can also be used with any Rack-enabled web framework.
To do so, just add
require ‘sass/plugin/rack’
use Sass::Plugin::Rack
to config.ru.
Then any Sass files in public/stylesheets/sass
will be compiled CSS files in public/stylesheets on every request.
To use Haml and Sass programatically,
check out the YARD documentation.
Formatting
Haml
The most basic element of Haml
is a shorthand for creating HTML:
%tagname{:attr1 => ‘value1’, :attr2 => ‘value2’} Contents
No end-tag is needed; Haml handles that automatically.
If you prefer HTML-style attributes, you can also use:
%tagname(attr1=‘value1’ attr2=‘value2’) Contents
Adding class and id attributes is even easier.
Haml uses the same syntax as the CSS that styles the document:
%tagname#id.class
In fact, when you’re using the <div> tag,
it becomes even easier.
Because <div> is such a common element,
a tag without a name defaults to a div. So
#foo Hello!
becomes
Haml uses indentation
to bring the individual elements to represent the HTML structure.
A tag’s children are indented beneath than the parent tag.
Again, a closing tag is automatically added.
For example:
%ul
%li Salt
%li Pepper
becomes:
- Salt
- Pepper
You can also put plain text as a child of an element:
%p
Hello,
World!
It’s also possible to embed Ruby code into Haml documents.
An equals sign, =, will output the result of the code.
A hyphen, -, will run the code but not output the result.
You can even use control statements
like if and while:
%p
Date/Time:
- now = DateTime.now
%strong= now
- if now > DateTime.parse(“December 31, 2006”)
= “Happy new ” + “year!”
Haml provides far more tools than those presented here.
Check out the reference documentation
for full details.
Indentation
Haml’s indentation can be made up of one or more tabs or spaces.
However, indentation must be consistent within a given document.
Hard tabs and spaces can’t be mixed,
and the same number of tabs or spaces must be used throughout.
Sass
Sass is an extension of CSS
that adds power and elegance to the basic language.
It allows you to use variables, nested rules,
mixins, inline imports,
and more, all with a fully CSS-compatible syntax.
Sass helps keep large stylesheets well-organized,
and get small stylesheets up and running quickly,
particularly with the help of
the Compass style library.
Sass has two syntaxes.
The one presented here, known as “SCSS” (for “Sassy CSS”),
is fully CSS-compatible.
The other (older) syntax, known as the indented syntax or just “Sass”,
is whitespace-sensitive and indentation-based.
For more information, see the reference documentation.
To run the following examples and see the CSS they produce,
put them in a file called test.scss and run sass test.scss.
Nesting
Sass avoids repetition by nesting selectors within one another.
The same thing works for properties.
table.hl {
margin: 2em 0;
td.ln { text-align: right; }
}
li {
font: {
family: serif;
weight: bold;
size: 1.2em;
}
}
Variables
Use the same color all over the place?
Need to do some math with height and width and text size?
Sass supports variables, math operations, and many useful functions.
$blue: #3bbfce;
$margin: 16px;
.content_navigation {
border-color: $blue;
color: darken($blue, 10%);
}
.border {
padding: $margin / 2;
margin: $margin / 2;
border-color: $blue;
}
Mixins
Even more powerful than variables,
mixins allow you to re-use whole chunks of CSS,
properties or selectors.
You can even give them arguments.
@mixin table-scaffolding {
th {
text-align: center;
font-weight: bold;
}
td, th { padding: 2px; }
}
@mixin left($dist) {
float: left;
margin-left: $dist;
}
#data {
@include left(10px);
@include table-scaffolding;
}
A comprehensive list of features is available
in the Sass reference.
Executables
The Haml gem includes several executables that are useful
for dealing with Haml and Sass from the command line.
haml
The haml executable transforms a source Haml file into HTML.
See haml --help for further information and options.
sass
The sass executable transforms a source Sass file into CSS.
See sass --help for further information and options.
html2haml
The html2haml executable attempts to transform HTML,
optionally with ERB markup, into Haml code.
Since HTML is so variable, this transformation is not always perfect;
it’s a good idea to have a human check the output of this tool.
See html2haml --help for further information and options.
sass-convert
The sass-convert executable converts between CSS, Sass, and SCSS.
When converting from CSS to Sass or SCSS,
nesting is applied where appropriate.
See sass-convert --help for further information and options.
Authors
Haml and Sass were created by Hampton Catlin
(hcatlin) and he is the author of the original implementation. However, Hampton
doesn’t even know his way around the code anymore and now occasionally consults
on the language issues. Hampton lives in Jacksonville, Florida and is the lead
mobile developer for Wikimedia.
Nathan Weizenbaum is the primary developer and architect of
the “modern” Ruby implementation of Haml. His hard work has kept the project
alive by endlessly answering forum posts, fixing bugs, refactoring, finding
speed improvements, writing documentation, implementing new features, and
getting Hampton coffee (a fitting task for a boy-genius). Nathan lives in
Seattle, Washington and while not being a student at the University of
Washington or working at an internship, he consults for Unspace Interactive.
Chris Eppstein is a core contributor to
Sass and the creator of Compass, the first Sass-based framework. Chris focuses
on making Sass more powerful, easy to use, and on ways to speed its adoption
through the web development community. Chris lives in San Jose, California with
his wife and daughter. He is the Software Architect for
Caring.com, a website devoted to the 34 Million caregivers
whose parents are sick or elderly, that uses Haml and Sass.
If you use this software, you must pay Hampton a compliment. And
buy Nathan some jelly beans. Maybe pet a kitten. Yeah. Pet that kitty.
Some of the work on Haml was supported by Unspace Interactive.
Beyond that, the implementation is licensed under the MIT License.
Okay, fine, I guess that means compliments aren’t required.