Copying Twitters Style - Integrating Index and Create Form on Same Page

I'd like to basically do what Twitter's stream does - have the create action and index action available on the same page, but I'm now getting an error, NilClass from the form.

Here's my view, then my code

class MistakesController < ApplicationController

  respond_to :html, :xml, :json

  before_filter :authenticate_user!

  def index
    @mistakes = Mistake.all
    @user = current_user

    respond_to do |t|
      t.html
    end
  end

  def create

    @mistake = Mistake.new(params[:mistake])
    @mistake.user = current_user

    respond_to do |f|
      if @mistake.save
        f.html {开发者_如何学Python redirect_to("/", :notice => 'cool') }
      else
        f.html { render :action => 'new' }
      end
    end
  end

  def new
    @new_mistake = Mistake.new
  end

  def show
    @mistake = Mistake.find(params[:id])
  end

end

and index.html.haml

%p test
%p= @user.email
= link_to "Create", new_mistake_path
- semantic_form_for @mistake do |form|
  = form.inputs :name => "Basic" do
    = form.input :message
    = form.input :notes
  = form.inputs :name => "Topics" do
    = form.input
  = form.buttons do
    = form.commit_button

I'm starting to go through the growing pains of creating a non-trivial rails app so any help would be great.

Thanks

EDIT:

Error Info

Message

undefined method `model_name' for NilClass:Class

Occurs when I view index.html.haml.

Try adding this to the index action of your controller

@mistake = Mistake.new

This is required in addition to the @mistakes variable you already have there...

You may not need a new action at all, since that form is now part of your index page. I'd recommend just getting rid of that action and having create redirect to index instead.

This is in addition to stephenmurdoch's suggestion above.