= Haml (XHTML Abstraction Markup Language)
Haml is a markup language
that's used to cleanly and simply describe the XHTML of any web document,
without the use of inline code.
Haml functions as a replacement
for inline page templating systems such as PHP, RHTML, and ASP.
However, Haml avoids the need for explicitly coding XHTML into the template,
because it is actually an abstract description of the XHTML,
with some code to generate dynamic content.
== Features
* Whitespace active
* Well-formatted markup
* DRY
* Follows CSS conventions
* Interpolates Ruby code
* Implements Rails templates with the .haml extension
== Authors
Haml was originally created by Hampton Catlin (hcatlin).
Help with the Ruby On Rails implementation and much of the documentation
by Jeff Hardy (packagethief).
Nathan Weizenbaum (Nex3) contributed the buffered-engine code,
along with many other enhancements
(including the silent-line syntax: "-").
If you use this software, you must pay Hampton a compliment.
Say something nice about it.
Beyond that, the implementation is licensed under the MIT License.
Ok, fine, I guess that means compliments aren't *required*.
== Formatting
Haml is sensitive to spacing and indentation;
it uses nesting to convey structure.
When you want an element to have children,
indent the lines below it using two spaces.
Remember, spaces are not the same as tabs.
For example:
#contact
%h1 Eugene Mumbai
%ul.info
%li.login eugene
%li.email eugene@example.com
is compiled to:
<div id='contact'>
<h1>Eugene Mumbai</h1>
<ul class='info'>
<li class='login'>eugene</li>
<li class='email'>eugene@example.com</li>
</ul>
</div>
== Characters with meaning to Haml
Various characters, when placed at a certain point in a line,
instruct Haml to render different types of things.
=== XHTML Tags
These characters render XHTML tags.
==== %
This element is placed at the beginning of a line.
It's followed immediately by the name of an element,
then optionally by modifiers (see below), a space,
and text to be rendered inside the element.
It creates an element in the form of <tt><element></element></tt>.
For example:
%one
%two
%three Hey there
is compiled to:
<one>
<two>
<three>Hey there</three>
</two>
</one>
Any string is a valid element name;
Haml will automatically generate opening and closing tags for any element.
==== {}
Brackets represent a Ruby hash
that is used for specifying the attributes of an element.
It is literally evaluated as a Ruby hash,
so logic will work in it and local variables may be used.
Quote characters within the attribute
will be replaced by appropriate escape sequences.
The hash is placed after the tag is defined.
For example:
%head{ :name => "doc_head" }
%script{ 'type' => "text/" + "javascript",
:src => "javascripts/script_#{2 + 7}" }
is compiled to:
<head name="doc_head">
<script src='javascripts/script_9' type='text/javascript'>
</script>
</head>
==== []
Square brackets follow a tag definition and contain a Ruby object
that is used to set the class and id of that tag.
The class is set to the object's class
(transformed to use underlines rather than camel case)
and the id is set to the object's class, followed by its id.
Because the id of an object is normally an obscure implementation detail,
this is most useful for elements that represent instances of Models.
For example:
# file: app/controllers/users_controller.rb
def show
@user = CrazyUser.find(15)
end
# file: app/views/users/show.haml
%div[@user]
%bar[290]/
Hello!
is compiled to:
<div class="crazy_user" id="crazy_user_15">
<bar class="fixnum" id="fixnum_581" />
Hello!
</div>
This is based off of DHH's SimplyHelpful syntax,
as presented at RailsConf Europe 2006.
==== /
The forward slash character, when placed at the end of a tag definition,
causes the tag to be self-closed.
For example:
%br/
%meta{:http-equiv => 'Content-Type', :content => 'text/html'}/
is compiled to:
<br />
<meta http-equiv='Content-Type' content='text/html' />
==== . and #
The period and pound sign are borrowed from CSS.
They are used as shortcuts to specify the <tt>class</tt>
and <tt>id</tt> attributes of an element, respectively.
Multiple class names can be specified in a similar way to CSS,
by chaining the class names together with periods.
They are placed immediately after the tag and before an attributes hash.
For example:
div#things
%span#rice Chicken Fried
%p.beans{ :food => 'true' } The magical fruit
%h1.class.otherclass#id La La La
is compiled to:
<div id='things'>
<span id='rice'>Chicken Fried</span>
<p class='beans' food='true'>The magical fruit</p>
<h1 class='class' id='id'>La La La</h1>
</div>
And,
#content
.articles
.article.title
Doogie Howser Comes Out
.article.date
2006-11-05
.article.entry
Neil Patrick Harris would like to dispel any rumors that he is straight
is compiled to:
<div id="content">
<div class="articles">
<div class="article title">Doogie Howser Comes Out</div>
<div class="article date">2006-11-05</div>
<div class="article entry">
Neil Patrick Harris would like to dispel any rumors that he is straight
</div>
</div>
</div>
==== Implicit Div Elements
Because the div element is used so often, it is the default element.
If you only define a class and/or id using the <tt>.</tt> or <tt>#</tt> syntax,
a div element is automatically used.
For example:
#collection
.item
.description What a cool item!
is the same as:
%div{:id => collection}
%div{:class => 'item'}
%div{:class => 'description'} What a cool item!
and is compiled to:
<div id='collection'>
<div class='item'>Broken record album</div>
<div class='description'>What a cool item!</div>
</div>
==== = and ~
<tt>=</tt> and <tt>~</tt> are placed at the end of a tag definition,
after class, id, and attribute declarations.
They're just shortcuts for inserting Ruby code into an element.
They work the same as <tt>=</tt> and <tt>~</tt> without a tag;
see below for documentation of those.
However, if the result is short enough,
it is displayed entirely on one line.
For example:
%p= "hello"
%h1~ 1 + 2
is not quite the same as:
%p
= "hello"
%h1
~ 1 + 2
It's compiled to:
<p>hello</p>
<h1>3</h1>
=== XHTML Helpers
==== No Special Character
If no special character appears at the beginning of a line,
the line is rendered as plain text.
For example:
%gee
%whiz
Wow this is cool!
is compiled to:
<gee>
<whiz>
Wow this is cool!
</whiz>
</gee>
==== !!!
When describing XHTML documents with Haml,
you can have a document type or XML prolog generated automatically
by including the characters <tt>!!!</tt>.
For example:
!!! XML
!!!
%html
%head
%title Myspace
%body
%h1 I am the international space station
%p Sign my guestbook
is compiled to:
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>Myspace</title>
</head>
<body>
<h1>I am the international space station</h1>
<p>Sign my guestbook</p>
</body>
</html>
You can also specify the version and type of XHTML after the <tt>!!!</tt>.
XHTML 1.0 Strict, Transitional, and Frameset and XHTML 1.1 are supported.
The default version is 1.0 and the default type is Transitional.
For example:
!!! 1.1
is compiled to:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
and
!!! Strict
is compiled to:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
If you're not using the UTF-8 characterset for your document,
you can specify which encoding should appear
in the XML prolog in a similar way.
For example:
!!! XML iso-8859-1
is compiled to:
<?xml version="1.0" encoding="iso-8859-1" ?>
==== /
The forward slash character, when placed at the beginning of a line,
wraps all text after it in an HTML comment.
For example:
%billabong
/ This is the billabong element
I like billabongs!
is compiled to:
<billabong>
<!-- This is the billabong element -->
I like billabongs!
</billabong>
The forward slash can also wrap indented sections of code. For example:
/
%p This doesn't render...
%div
%h1 Because it's commented out!
is compiled to:
<!--
<p>This doesn't render...</p>
<div>
<h1>Because it's commented out!</h1>
</div>
-->
You can also use Internet Explorer conditional comments
(about)[http://www.quirksmode.org/css/condcom.html]
by enclosing the condition in square brackets after the <tt>/</tt>.
For example:
/[if IE]
%a{ :href => 'http://www.mozilla.com/en-US/firefox/' }
%h1 Get Firefox
is compiled to:
<!--[if IE]>
<a href='http://www.mozilla.com/en-US/firefox/'>
<h1>Get Firefox</h1>
</a>
<![endif]-->
==== \
The backslash character escapes the first character of a line,
allowing use of otherwise interpreted characters as plain text.
For example:
%title
= @title
\- MySite
is compiled to:
<title>
MyPage
- MySite
</title>
==== |
The pipe character designates a multiline string.
It's placed at the end of a line
and means that all following lines that end with <tt>|</tt>
will be evaluated as though they were on the same line.
For example:
%whoo
%hoo I think this might get |
pretty long so I should |
probably make it |
multiline so it doesn't |
look awful. |
%p This is short.
is compiled to:
%hoo I think this might get |
pretty long so I should |
probably make it |
multiline so it doesn't |
look awful. |
=== Ruby evaluators
==== =
The equals character is followed by Ruby code,
which is evaluated and the output inserted into the document as plain text.
For example:
%p
= ['hi', 'there', 'reader!'].join " "
= "yo"
is compiled to:
<p>
hi there reader!
yo
</p>
==== ~
The tilde character works the same as the equals character,
but the output is modified in such a way
that newlines in whitespace-sensitive elements work properly.
For example:
%foo
= "Woah <pre> this is \n</pre> crazy"
%foo2
~ "Woah <pre> this is \n</pre> crazy"
is compiled to:
<foo>
Woah <pre> this is
</pre> crazy
</foo>
<foo2>
Woah <pre> this is 
</pre> crazy
</foo2>
If the ~ character isn't followed by text,
it doesn't evaluate Ruby at all.
Instead, an indented section following it will be rendered
in a whitespace-sensitive manner,
using HTML encodings for newlines.
For example:
For example:
.house
%pre
~
/^^^\
|[] []|
|_____|
is compiled to:
<div class="house">
<pre>

 /^^^\
|[] []|
|_____|

</pre>
</div>
==== -
The hyphen character makes the text following it into "silent script":
Ruby script that is evaluated, but not output.
<b>It is not recommended that you use this widely;
almost all processing code and logic should be restricted
to the Controller, the Helper, or partials.</b>
For example:
- foo = "hello"
- foo << " there"
- foo << " you!"
%p= foo
is compiled to:
<p>
hello there you!
</p>
===== Blocks
Ruby blocks, like XHTML tags, don't need to be explicitly closed in Haml.
Rather, they're automatically closed, based on indentation.
A block begins whenever the indentation is increased
after a silent script command.
It ends when the indentation decreases
(as long as it's not an +else+ clause or something similar).
For example:
- (42...47).each do |i|
%p= i
%p See, I can count!
is compiled to:
<p>
42
</p>
<p>
43
</p>
<p>
44
</p>
<p>
45
</p>
<p>
46
</p>
Another example:
%p
- case 2
- when 1
= "1!"
- when 2
= "2?"
- when 3
= "3."
is compiled to:
<p>
2?
</p>
== Using Haml as a Rails plugin
Write Rails templates with the .haml extension.
For example:
# file: app/views/movies/teen_wolf.haml
%html
%head
%title= "Teen Wolf (1985)"
%body
#contents
%h1 "A highschooler discovers that he is a werewolf"
%ul.cast
%li "Scott Howard"
%li "Rupert 'Stiles' Stilinski"
%li "Lisa 'Boof' Marconi"
%li "Lewis"
is compiled to:
<html>
<head>
<title>Teen Wolf (1985)</title>
</head>
<body>
<div id='contents'>
<h1>A highschooler discovers that he is a werewolf</h1>
<ul class='cast'>
<li>Scott Howard</li>
<li>Rupert 'Stiles' Stilinski</li>
<li>Lisa 'Boof' Marconi</li>
<li>Lewis</li>
</ul>
</div>
</body>
</html>
You can access instance variables in Haml templates
the same way you do in ERb templates.
Helper methods are also available in Haml templates.
For example:
# file: app/controllers/movies_controller.rb
class MoviesController < ApplicationController
def index
@title = "Teen Wolf"
end
end
# file: app/views/movies/index.haml
#content
.title
%h1= @title
= link_to 'Home', home_url
may be compiled to:
<div id='content'>
<div class='title'>
<h1>Teen Wolf</h1>
<a href='/'>Home</a>
</div>
</div>
=== Setting Options
Options can be set by setting the hash <tt>Haml::Template.options</tt>
from <tt>environment.rb</tt>.
Available options are:
[<tt>:suppress_eval</tt>] Whether or not attribute hashes and Ruby scripts
designated by <tt>=</tt> or <tt>~</tt> should be
evaluated. If this is true, said scripts are
rendered as empty strings. Defaults to false.
[<tt>:precompiled</tt>] A string containing a precompiled Haml template.
If this is passed, <tt>template</tt> is ignored
and no precompilation is done.
[<tt>:attr_wrapper</tt>] The character that should wrap element attributes.
This defaults to <tt>'</tt> (an apostrophe). Characters
of this type within the attributes will be escaped
(e.g. by replacing them with <tt>'</tt>) if
the character is an apostrophe or a quotation mark.
[<tt>:locals</tt>] The local variables that will be available within the
template. For instance, if <tt>:locals</tt> is
<tt>{ :foo => "bar" }</tt>, then within the template,
<tt>= foo</tt> will produce <tt>bar</tt>.
---
Copyright (c) 2006 Hampton Catlin
Licensed under the MIT License
