= 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 PHP, RHTML, and ASP.
However, Haml avoids the need for explicitly coding XHTML into the template,
because it iself is a 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) contribued 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. 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. At
the moment, though, it doesn't see local variables. 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 definiton 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 and used as shortcuts to specify the
<tt>class</tt> and <tt>id</tt> attributes of an element, respectively. 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#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>
==== Assumed Divs
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. For example:
%p= "hello"
%h1~ 1 + 2
is the same as:
%p
= "hello"
%h1
~ 1 + 2
and is compiled to:
<p>
hello
</p>
<h1>
3
</h1>
=== XHTML Helpers
==== No Special Character
If no special character appears at the beginning of a line, it 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
generated automatically by including the characters <tt>!!!</tt> as the first
line in your document. Example:
!!!
%html
%head
%title Myspace
%body
%h1 I am the international space station
%p Sign my guestbook
is compiled to:
<!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>
==== /
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 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>
==== -
The hyphen character makes the text following it into "silent script", or
Ruby script that is evaluated, but not output.
<b>It is not reccomended that you use this widely; almost all processing
code and logic should be kept 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
Like XHTML tags, you don't need to explicity close your Ruby blocks in
HAML. Rather, they're automatically closed based on tabs. A block begins
whenever the indentation is increased after a silent script command, and
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. 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. 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>
---
Copyright (c) 2006 Hampton Catlin
Licensed under the MIT License
89a10b9dfe