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.
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.sass
to compile them. For more information on these commands, check out
haml --help
sass --help
To install Haml and Sass as a Rails plugin,
just run haml --rails path/to/rails/app
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.
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
<div id='foo'>Hello!</div>
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:
<ul>
<li>Salt</li>
<li>Pepper</li>
</ul>
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 in the Haml module.
At its most basic, Sass is just another way of writing CSS. Although it's very much like normal CSS, the basic syntax offers a few helpful features: indentation indicates the properties in a rule, rather than non-DRY brackets; and newlines indicate the end of a properties, rather than a semicolon. For example:
#main
background-color: #f00
width: 98%
becomes:
#main {
background-color: #f00;
width: 98% }
However, Sass provides much more than a way to make CSS look nice. In CSS, it's important to have accurate selectors, so your styles don't just apply to everything. However, in order to do this, you need to use nested element selectors. These get very ugly very quickly. I'm sure everyone's had to write something like "#main .sidebar .top p h1 a", followed by "#main .sidebar .top p h1 a:visited" and "#main .sidebar .top p h1 a:hover". Well, Sass gets rid of that. Like Haml, it uses indentation to indicate the structure of the document. So, what was:
#main {
width: 90%;
}
#main p {
border-style: solid;
border-width: 1px;
border-color: #00f;
}
#main p a {
text-decoration: none;
font-weight: bold;
}
#main p a:hover {
text-decoration: underline;
}
becomes:
#main
width: 90%
p
border-style: solid
border-width: 1px
border-color: #00f
a
text-decoration: none
font-weight: bold
a:hover
text-decoration: underline
Pretty nice, no? Well, it gets better.
One of the main complaints against CSS is that it doesn't allow variables.
What if have a color or a width you re-use all the time?
In CSS, you just have to re-type it each time,
which is a nightmare when you decide to change it later.
Not so for Sass!
You can use the ! character to set variables.
Then, if you put = after your property name,
you can set it to a variable.
For example:
!note_bg= #55aaff
#main
width: 70%
.note
background-color = !note_bg
p
width: 5em
background-color = !note_bg
becomes:
#main {
width: 70%; }
#main .note {
background-color: #55aaff; }
#main p {
width: 5em;
background-color: #55aaff; }
You can even do simple arithmetic operations with variables, adding numbers and even colors together:
!main_bg= #46ar12
!main_width= 40em
#main
background-color = !main_bg
width = !main_width
.sidebar
background-color = !main_bg + #333333
width = !main_width - 25em
becomes:
#main {
background-color: #46a312;
width: 40em; }
#main .sidebar {
background-color: #79d645;
width: 15em; }
Taking the idea of variables a bit further are mixins. These let you group whole bunches of CSS properties into a single directive and then include those anywhere you want:
=blue-border
border:
color: blue
width: 2px
style: dotted
.comment
+blue-border
padding: 2px
margin: 10px 0
.reply
+blue-border
becomes:
.comment {
border-color: blue;
border-width: 2px;
border-style: dotted;
padding: 2px;
margin: 10px 0;
}
.reply {
border-color: blue;
border-width: 2px;
border-style: dotted;
}
A comprehensive list of features is in the documentation for the Sass module.
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.
The Haml gem includes several executables that are useful for dealing with Haml and Sass from the command line.
The haml executable transforms a source Haml file into HTML.
See haml --help for further information and options.
The sass executable transforms a source Sass file into CSS.
See sass --help for further information and options.
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.
The css2sass executable attempts to transform CSS into Sass code.
This transformation attempts to use Sass nesting where possible.
See css2sass --help for further information and options.
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.