[updates to HelloWorld.lhs
Jeremy Shaw <jeremy@seereason.com>**20100413201817
 Ignore-this: 74cdcaaaf1a4f719158584e79f280463
] hunk ./HelloWorld.lhs 1
+<!--
+
+> {-# LANGUAGE CPP #-}
+
+-->
+
hunk ./HelloWorld.lhs 17
-> main = simpleHTTP nullConf $ ok (toResponse "Hello, World!")
+> main = simpleHTTP nullConf $ ok "Hello, World!"
hunk ./HelloWorld.lhs 50
+<p>The top-level function <code>simpleHTTP</code> is what actually starts the programming listening for incoming HTTP requests.</p>
+
hunk ./HelloWorld.lhs 55
+
+<p>The first argument is some simple server configuration information. It is defined as:</p>
+
+#ifdef HsColour
+> data Conf = Conf { port :: Int
+>                  , validator :: Maybe (Response -> IO Response) 
+>                  }
+#endif
+
+<p>The <code>port</code> is the TCP port to listen on for incoming connection. The <code>validator</code> is used to do on-the-fly validation of output during development. It's will eventually be described elsewhere is this document.</p>
+
+<p>The default config is <code>nullConf</code> which is simply defined as:</p>
+
+#ifdef HsColour
+> -- | Default configuration contains no validator and the port is set to 8000
+> nullConf :: Conf
+> nullConf = Conf { port      = 8000
+>                 , validator  = Nothing
+>                 }
+#endif
+
+<p>The second argument is a bit more interesting. The <code>ServerPartT IO a</code> is the code that actually processes an incoming HTTP <code>Request</code> and generates a <code>Response</code>. The <code>ServerPartT IO</code> monad is essentially a fancy way of writing a function with the type:</p>
+
+#ifdef HsColour
+> Request -> IO Response
+#endif
+
+<p><code>simpleHTTP</code> processes each incoming request in it's own thread. It will parse the <code>Request</code> call your <code>ServerPartT</code> handler, and then return the <code>Response</code> to the client. When developing your server part, it is natural to think about things as if you are writing a program which processes a single <code>Request</code>, generates a <code>Response</code>, and exits. However it is important when doing I/O, such as writing files to disk, or talking to a ''database'' to remember that there may be other threads running simultaneously.</p>
+
+
+<p>In this example, our server part is simply:</p>
+
+#ifdef HsColour
+> ok "Hello, World!"
+#endif
+
+<p><code>ok</code> is one of several combinators which can be used to set the HTTP response code. In this case, it will set the response code to <code>200 OK</code>.</p>
+
+<p>The body of the response will be "Hello, World!".</p>
+
+<p>The <code>String</code> "Hello, World!" is turned into a <code>Response</code> because simpleHTTP calls <code>toResponse</code> from the <code>ToMessage</code> class on it. Often times we will opt to make this call explicit rather than implicit. For example:</p>
+
+#ifdef HsColour
+> main :: IO ()
+> main = simpleHTTP nullConf $ ok (toResponse "Hello, World!")
+#endif
+
+<p>The <code>toResponse</code> function takes care of setting the <code>Content-type</code> and converting the value into a lazy <code>ByteString</code> which will be sent back to the client. Happstack comes with pre-defined <code>ToMessage</code> instances for many types such as <code>Text.Html.Html</code>, <code>Text.XHtml.Html</code>, <code>String</code>, the types from HSP, and more.</p>
+
hunk ./Main.lhs 5
-  <title>Data Serialization, Deserialization, and Migration using HAppS-Data</title>
+  <title>Crash Course in Happstack</title>
hunk ./Makefile 55
-	HsColour -css -partial $< -o$@ -lit
+	./HsColour -css -partial $< -o$@ -lit
hunk ./blog.css 4
-  width: 40em;
+  width: 35em;
hunk ./blog.css 24
+code
+{  }