1. new in this version
2. build a web 2.0 app in happstack
3. why happstack is cool
4. getting started with happstack
5. prerequisites
6. cabal install me
7. first shot at happstack
8. url handling
9. basic HTML inclusion
10. templates
11. stringtemplate basics
12. debugging
13. form data: get and post
14. form data: file uploads
15. cookies
16. introduction to macid
17. first steps with macid
18. scaling with multimaster
19. using macid safely
20. macid dummy data
21. changing the data model
22. macid stress test
23. limitations of macid
24. foreign characters
25. IxSets
26. cron jobs
27. thanks
28. appendix (floundering in ghci)

StringTemplate Basics

In the previous section we rendered a template in ghci using the following command

*Main Misc View Text.StringTemplate> do templates <- directoryGroup "templates" ; writeFile "output.html" ( renderTemplateGroup templates ([]::[(String,String)]) "templatesdontrepeatyourself" )

Let's look more carefully at these functions.

• The directoryGroup function reads in all *.st type files in a directory, and returns an IO STGroup value, which is basically a group of StringTemplates.
  *Main Misc View Text.StringTemplate> :t (directoryGroup :: String -> IO (STGroup String))
  The actual type of directoryGroup is a little less concrete than the above, and uses type classes.
  Our :t command gives directoryGroup a concrete type, and since there's no error, we know it typechecks.
• renderTemplateGroup takes an STGroup, some template key/value pairs, and a named template, and renders the template if it is found in the STGroup. If it is not found, an error is returned.
  *Main Misc View Text.StringTemplate> :t renderTemplateGroup
  renderTemplateGroup :: STGroup String -> [(String, String)] -> String -> String

Next, let's look at a slightly more involved example of StringTemplate usage than we've seen so far.

• The controller: myFavoriteAnimal, in src/ControllerBasic.hs
  a snip:
    renderTemplateGroup templates
      [("favoriteAnimal", "Tyrannasaurus Rex") , ("leastFavoriteAnimal","Bambi")] $ "myFavoriteAnimalBase"
• The rendered page: my favorite animal
• The template: templates/myFavoriteAnimalBase.st
• A template included from inside an included templates: leastFavoriteAnimal()

Try to gain an understanding of the most important features in the StringTemplate system by getting a sense of how the my-favorite-animal page got generated.

When you're done doing that, you should have enough StringTemplate knowledge to shoot yourself in the foot :)

For a more in depth look at StringTemplate, see the following:

• stringtemplate.org
• HStringTemplate, a haskell port of StringTemplate on hackage
• fmapfixreturn, Sterling Clover's blog

And now, on to debugging.