107 lines
3.9 KiB
Plaintext
107 lines
3.9 KiB
Plaintext
FIXME documentation is out of date in a few places.
|
|
|
|
> {-# LANGUAGE QuasiQuotes #-}
|
|
> {-# LANGUAGE TemplateHaskell #-}
|
|
> {-# LANGUAGE TypeFamilies #-}
|
|
|
|
I in general recommend type signatures for everything. However, I wanted
|
|
to show in this example how it is possible to get away without the
|
|
signatures.
|
|
|
|
> {-# OPTIONS_GHC -fno-warn-missing-signatures #-}
|
|
|
|
There are only two imports: Yesod includes all of the code we need for creating
|
|
a web application, while Network.Wai.Handler.SimpleServer allows us to test our
|
|
application easily. A Yesod app can in general run on any WAI handler, so this
|
|
application is easily convertible to CGI, FastCGI, or even run on the Happstack
|
|
server.
|
|
|
|
> import Yesod
|
|
> import Network.Wai.Handler.SimpleServer
|
|
|
|
The easiest way to start writing a Yesod app is to follow the Yesod typeclass.
|
|
You define some data type which will contain all the specific settings and data
|
|
you want in your application. This might include database connections,
|
|
templates, etc. It's entirely up to you.
|
|
|
|
For our simple demonstration, we need no extra data, so we simply define Fact
|
|
as:
|
|
|
|
> data Fact = Fact
|
|
|
|
Now we need to declare an instance of Yesod for Fact. The most important
|
|
function to declare is handlers, which defines which functions deal with which
|
|
resources (aka URLs).
|
|
|
|
You can declare the function however you want, but Yesod.Resource declares a
|
|
convenient "resources" quasi-quoter which takes YAML content and generates the
|
|
function for you. There is a lot of cool stuff to do with representations going
|
|
on here, but this is not the appropriate place to discuss it.
|
|
|
|
|
|
|
|
The structure is very simply: top level key is a "resource pattern". A resource pattern is simply a bunch of slash-separated strings, called "resource pattern pieces". There are three special ways to start a piece:
|
|
|
|
* $: will take any string
|
|
|
|
* \#: will take any integer
|
|
|
|
* \*: will "slurp" up all the remaining pieces. Useful for something like
|
|
/static/*filepath
|
|
|
|
Otherwise, the piece is treated as a literal string which must be matched.
|
|
|
|
|
|
Now we have a mapping of verbs to handler functions. We could instead simply
|
|
specify a single function which handles all verbs. (Note: a verb is just a
|
|
request method.)
|
|
|
|
> $(mkYesod "Fact" [$parseRoutes|
|
|
> / Index GET
|
|
> /#num FactR GET
|
|
> /fact FactRedirect GET
|
|
> |])
|
|
|
|
> instance Yesod Fact where
|
|
> approot _ = "http://localhost:3000"
|
|
|
|
This does what it looks like: serves a static HTML file.
|
|
|
|
> getIndex = sendFile TypeHtml "examples/fact.html" >> return ()
|
|
|
|
HtmlObject is a funny beast. Basically, it allows multiple representations of
|
|
data, all with HTML entities escaped properly. These representations include:
|
|
|
|
* Simple HTML document (only recommended for testing).
|
|
* JSON (great for Ajax)
|
|
* Input to a HStringTemplate (great for no-Javascript fallback).
|
|
|
|
For simplicity here, we don't include a template, though it would be trivial to
|
|
do so (see the hellotemplate example).
|
|
|
|
> getFactR :: Integer -> Handler y ChooseRep -- FIXME remove
|
|
> getFactR _i = error "FIXME" {-simpleApplyLayout "Factorial result" $ cs
|
|
> [ ("input", show i)
|
|
> , ("result", show $ product [1..fromIntegral i :: Integer])
|
|
> ]-}
|
|
|
|
I've decided to have a redirect instead of serving the some data in two
|
|
locations. It fits in more properly with the RESTful principal of one name for
|
|
one piece of data.
|
|
|
|
> getFactRedirect :: Handler y ()
|
|
> getFactRedirect = do
|
|
> res <- runFormPost $ catchFormError
|
|
> $ checkInteger
|
|
> $ required
|
|
> $ input "num"
|
|
> let i = either (const "1") show res
|
|
> redirect RedirectPermanent $ "../" ++ i ++ "/"
|
|
|
|
You could replace this main to use any WAI handler you want. For production,
|
|
you could use CGI, FastCGI or a more powerful server. Just check out Hackage
|
|
for options (any package starting hack-handler- should suffice).
|
|
|
|
> main :: IO ()
|
|
> main = putStrLn "Running..." >> toWaiApp Fact >>= run 3000
|