Module Haml
In: lib/haml/exec.rb
lib/haml/html.rb
lib/haml/error.rb
lib/haml/template.rb
lib/haml/helpers.rb
lib/haml/engine.rb
lib/haml/helpers/action_view_extensions.rb
lib/haml.rb

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, ERB, 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
  • Integrates Ruby code
  • Implements Rails templates with the .haml extension

Using Haml

Haml can be used in two ways: as a plugin for Ruby on Rails, and as a standalone Ruby module.

Sass can be used in several ways: As a template engine for Ruby on Rails or Merb, or as a standalone engine. The first step for all of these is to install the Haml gem:

  gem install haml

To enable it as a Rails plugin, then run

  haml --rails path/to/rails/app

Haml is enabled in Merb by default, so Merb users don‘t have to do anything more.

Once it‘s installed, all view files with the ".haml" extension (or ".html.haml" for Merb or edge Rails) will be compiled using Haml.

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 (this example uses Rails, but the principle for Merb is the same):

  # 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>

Ruby Module

Haml can also be used completely separately from Rails and ActionView. To do this, install the gem with RubyGems:

  gem install haml

You can then use it by including the "haml" gem in Ruby code, and using Haml::Engine like so:

  engine = Haml::Engine.new("%p Haml code!")
  engine.render #=> "<p>Haml code!</p>\n"

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.

%

The percent character 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 <element></element>. 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' />

Some tags are automatically closed, as long as they have no content. meta, img, link, script, br, and hr tags are closed by default. This list can be customized by setting the :autoclose option (see below). For example:

  %br
  %meta{'http-equiv' => 'Content-Type', :content => 'text/html'}

is also 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 class and id 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 otherclass' 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 . or # 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'>
      <div class='description'>What a cool item!</div>
    </div>
  </div>

=

= is placed at the end of a tag definition, after class, id, and attribute declarations. It‘s just a shortcut for inserting Ruby code into an element. It works the same as = without a tag: it inserts the result of the Ruby code into the template. However, if the result is short enough, it is displayed entirely on one line. For example:

  %p= "hello"

is not quite the same as:

  %p
    = "hello"

It‘s compiled to:

  <p>hello</p>

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 !!!. 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 !!!. 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 character set 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:

  %peanutbutterjelly
    / This is the peanutbutterjelly element
    I like sandwiches!

is compiled to:

  <peanutbutterjelly>
    <!-- This is the peanutbutterjelly element -->
    I like sandwiches!
  </peanutbutterjelly>

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) by enclosing the condition in square brackets after the /. 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 | 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:

  <whoo>
    <hoo>
      I think this might get pretty long so I should probably make it multiline so it doesn't look awful.
    </hoo>
  </whoo>

:

The colon character designates a filter. This allows you to pass an indented block of text as input to another filtering program and add the result to the output of Haml. The syntax is simply a colon followed by the name of the filter. For example,

  %p
    :markdown
      Textile
      =======

      Hello, *World*

is compiled to

  <p>
    <h1>Textile</h1>

    <p>Hello, <em>World</em></p>
  </p>

Haml has the following filters defined:

plain
Does not parse the filtered text. This is useful for large blocks of text without HTML tags, when you don‘t want lines starting with . or - to be parsed.
ruby
Parses the filtered text with the normal Ruby interpreter. All output sent to $stdout, like with puts, is output into the Haml document. Not available if the suppress_eval option is set to true.
preserve
Inserts the filtered text into the template with whitespace preserved. preserved blocks of text aren‘t indented, and newlines are replaced with the HTML escape code for newlines, to preserve nice-looking output.
erb
Parses the filtered text with ERB, like an RHTML template. Not available if the suppress_eval option is set to true. At the moment, this doesn‘t support access to variables defined by Ruby on Rails or Haml code.
sass
Parses the filtered text with Sass to produce CSS output.
redcloth
Parses the filtered text with RedCloth (whytheluckystiff.net/ruby/redcloth), which uses both Textile and Markdown syntax. Only works if RedCloth is installed.
textile
Parses the filtered text with Textile (www.textism.com/tools/textile). Only works if RedCloth is installed.
markdown
Parses the filtered text with Markdown (daringfireball.net/projects/markdown). Only works if RedCloth or BlueCloth (www.deveiate.org/projects/BlueCloth) is installed (BlueCloth takes precedence if both are installed).

You can also define your own filters (see Setting Options, below).

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>

You can also use two equal signs, ==, along with conventional Ruby string-embedding syntax to easily embed Ruby code in otherwise static text. For example:

  %p
    == 1 + 1 = #{1 + 1}

is compiled to:

  <p>
    1 + 1 = 2
  </p>

-

The hyphen character makes the text following it into "silent script": Ruby script that is evaluated, but not output.

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.

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>

-#

The hyphen followed immediately by the pound sign signifies a silent comment. Any text following this isn‘t rendered in the resulting document at all.

For example:

%p foo -# This is a comment %p bar

is compiled to:

<p>foo</p> <p>bar</p>

Other Useful Things

Helpers

Haml offers a bunch of helpers that are useful for doing stuff like preserving whitespace, creating nicely indented output for user-defined helpers, and other useful things. The helpers are all documented in the Haml::Helpers and Haml::Helpers::ActionViewExtensions modules.

Haml Options

Options can be set by setting the hash Haml::Template.options from environment.rb in Rails, or by passing an options hash to Haml::Engine. Available options are:

:suppress_eval
Whether or not attribute hashes and Ruby scripts designated by = or ~ should be evaluated. If this is true, said scripts are rendered as empty strings. Defaults to false.
:attr_wrapper
The character that should wrap element attributes. This defaults to (an apostrophe). Characters of this type within the attributes will be escaped (e.g. by replacing them with &apos;) if the character is an apostrophe or a quotation mark.
:filename
The name of the Haml file being parsed. This is only used as information when exceptions are raised. This is automatically assigned when working through ActionView, so it‘s really only useful for the user to assign when dealing with Haml programatically.
:filters
A hash of filters that can be applied to Haml code. The keys are the string names of the filters; the values are references to the classes of the filters. User-defined filters should always have lowercase keys, and should have:
  • An initialize method that accepts one parameter, the text to be filtered.
  • A render method that returns the result of the filtering.
:locals
The local variables that will be available within the template. For instance, if :locals is { :foo => "bar" }, then within the template, = foo will produce bar.
:autoclose
A list of tag names that should be automatically self-closed if they have no content. Defaults to [‘meta’, ‘img’, ‘link’, ‘script’, ‘br’, ‘hr’].

Classes and Modules

Module Haml::Error
Module Haml::Helpers
Class Haml::Engine
Class Haml::HTML
Class Haml::HamlError
Class Haml::SyntaxError
Class Haml::Template

[Validate]