example.jade

:model
  form(user)
    p
      field(name)
    p
      field(email)
    p
      field(summary, as: 'textarea')
    buttons

old.jade

form(method="post", id="user-model-form")
  p
    input(type="text", name="user[name]", value=user.name)
    - if (user.errors.name)
      p.error= user.errors.name
  p
    input(type="text", name="user[email]", value=user.email)
    - if (user.errors.email)
      p.error= user.errors.email
  p.buttons
    - if (user.isNew)
      input(type="submit", value="Save")
    - else
      input(type="submit", value="Update")

output.html

<form id="user-model-form" method="post">
 <p>
  <label for="user[name]">Name:</label>
  <input type="text" value="Tobi" name="user[name]"/></p>
 <p>
  <label for="user[email]">Email:</label>
  <input type="text" value="vision-media.ca" name="user[email]"/>
   <p class="error">Invalid email</p></p>
 <p>
  <label for="user[summary]">Summary:</label>
  <textarea name="user[summary]">Tobi is a ferret, he is supes cool.</textarea></p>
 <p class="buttons">
  <input type="submit" value="Update"/></p>
  <input type="hidden" name="_method" value="put"/></form>

rails-is-lame.erb

<% form_for(@user) do |f| %>
  <p>
    <%= f.label :name %>
    <%= f.text_field :name %>
  </p>
  <p>
    <%= f.label :name %>
    <%= f.text_field :email %>
  </p>
  <p>
    <%= f.label :summary %>
    <%= f.text_area :summary %>
  </p>
  <p class="buttons">
    <%= f.submit %>
  </p>
<% end %>

visitor.js

// First define a filter named "model",
// which accepts a node (a Block node),
// and the parent Compiler

jade.filters.model = function(block, compiler){
    // pass the block / previous options to our new Visitor
    return new Visitor(block, compiler.options).compile();
};

function Visitor(node, options) {
    // "super" to the Compiler() constructor
    Compiler.call(this, node, options);
}

// Inherit from Compiler

Visitor.prototype.__proto__ = Compiler.prototype;

// Overwrite visitTag method 

Visitor.prototype.visitTag = function(node){
    var parent = Compiler.prototype.visitTag;
    switch (node.name) {
        case 'form':
            // Store the record variable name,
            // in our case "user" is our first
            // anonymous attribute
            this.record = node.attrs[0].name;
            // remove the record name attribute
            node.removeAttribute(this.record);
            node.setAttribute('id', '"' + this.record + '-model-form"');
            node.setAttribute('method', '"post"');

            // when the record is not new, we probably want a _method hidden
            // field to tell our server to use PUT with frameworks like Express
            var code = new nodes.Code('if (!' + this.record + '.new)');
            var put = new nodes.Tag('input');
            put.setAttribute('type', '"hidden"');
            put.setAttribute('name', '"_method"');
            put.setAttribute('value', '"put"');
            code.block = new nodes.Block(put);
            node.block.push(code);

            parent.call(this, node);
            break;
        case 'field':
            // Grab "as" attribute, defaulting it to "text"
            // perform some surgery on it since it IS literal JavaScript
            var name = node.attrs[0].name,
                as = (node.getAttribute('as') || 'text').trim().replace(/'/g, ''),
                capitalized = name.charAt(0).toUpperCase() + name.slice(1);

            // Field label
            var label = new nodes.Tag('label');
            label.setAttribute('for', '"' + this.record + '[' + name + ']"');
            label.block.push(new nodes.Text(capitalized + ':'));
            parent.call(this, label);

            // Field input
            switch (as) {
                case 'textarea':
                    var code = new nodes.Code(this.record + '.' + name, true, true);
                    node = new nodes.Tag('textarea');
                    node.block.push(code);
                    break;
                case 'text':
                    node = new nodes.Tag('input');
                    node.setAttribute('type', '"text"');
                    node.setAttribute('value', this.record + '.' + name);
            }
            node.setAttribute('name', '"' + this.record + '[' + name + ']"');
            parent.call(this, node);

            // Potential error tag
            var err = this.record + '.errors.' + name;
            node = new nodes.Code('if (' + err + ')');
            node.block = new nodes.Block;
            var p = new nodes.Tag('p', new nodes.Block(new nodes.Code(err, true, true)));
            node.block.push(p);

            Visitor.prototype.visitCode.call(this, node);
            break;
        case 'buttons':
            // Generate context sensative buttons which
            // check the record's state.
            node = new nodes.Tag('input');
            node.setAttribute('type', '"submit"');
            node.setAttribute('value', this.record + '.new ? "Save" : "Update"');
            var p = new nodes.Tag('p', new nodes.Block(node));
            p.setAttribute('class', '"buttons"');
            parent.call(this, p);
            break;
        default:
            parent.call(this, node);
    }
};