anchor.diff:  
   ==== Cabal file
   
  -Whether directly using +cabal+, or indirectly using +yesod devel+, building
  +Whether directly using +stack+, or indirectly using +stack exec -- yesod devel+, building
   your code will always go through the cabal file. If you open the file, you'll
   see that there are both library and executable blocks. If the +library-only+
   flag is turned on, then the executable block is not built.  This is how +yesod
  
positive.code: * Add it to the +Application.hs+ file.
  * Put a module statement at the top, and an +import Import+ line below it.
  
  You can use the +yesod add-handler+ command to automate the last three steps.
  
  === widgetFile
  
  
negative.code: 
  === How to Scaffold
  
  The yesod-bin package installs an executable (conveniently named
  _yesod_ as well). This executable provides a few commands (run _stack
  exec -- yesod --help_ to get a list). In order to generate a
  scaffolding, the command is _stack new my-project
  yesod-postgres_. This will generate a scaffolding site with a postgres
  database backend in a directory named +my-project+. You can see the
  other available templates using the command *stack templates*.
  
  The key thing differing in various available templates (from the
  *stack templates* command) is the database backend. You get a few
  choices here, including SQL and MongoDB backends, as well as
  "yesod-simple" template to include no database support.  This last
  option also turns off a few extra dependencies, giving you a leaner
  overall site. The remainder of this chapter will focus on the
  scaffoldings for one of the database backends. There will be minor
  differences for the yesod-simple backend.
  
  After creating your files, install the yesod command line tool inside
  the project: *stack build yesod-bin cabal-install*. Then do a *stack
  build* inside the directory.  In particular, the commands provided
  will ensure that any missing dependencies are built and installed.
  
  Finally, to launch your development site, you would use +stack exec --
  yesod devel+.  This site will automatically rebuild and reload
  whenever you change your code.
  
  === File Structure
  
  