+module Main where +import HAppS + +data MyState = MyState deriving (Read,Show) + +instance StartState MyState where + startStateM = return $ MyState +instance Serialize MyState where + typeString _ = "MyState" + encodeStringM = defaultEncodeStringM + decodeStringM = defaultDecodeStringM + +app :: Method -> Host -> [String] -> Ev MyState Request Result +app _ _ _ = do + addSideEffect 10 $ putStrLn "Hello World!" + sresult 200 "Hello World!" + +main = stdMain $ simpleHTTP "" [] app :*: End ++
+This simple program returns the string "Hello World!" to the +browser and prints it on the console where you run it. +
+ ++HAppS offers some easy ways to read and write XML and apply XSLT transformations +to the generated XML. +
++The following example shows how to generate XML from a datatype and how to +serialize it. Additionally a XSLT [9] stylesheet is used to +transform the XML into HTML. If you don't know how XSLT works, try a result +from [10] to learn it, it is an easy way to separate your +date from the representation. +
+
+To run the example, copy the following code into a file and compile it. The
+ToElement instance of Books requires the use of the
+module Main where
+import HAppS
+
+data MyState = MyState deriving (Read,Show)
+
+instance StartState MyState where
+ startStateM = return $ MyState
+instance Serialize MyState where
+ typeString _ = "MyState"
+ encodeStringM = defaultEncodeStringM
+ decodeStringM = defaultDecodeStringM
+
+type Books = [Book]
+instance ToElement Books where
+ toElement bs = listElem "Books" [] $ map toElement bs
+
+data Book = Book {author::String, title::String, content::String}
+instance ToElement Book where
+ toElement b = textElem "Book"
+ [("title", title b)
+ ,("author", author b)] $ content b
+
+app :: Method -> Host -> [String] -> Ev MyState Request Result
+app GET _ ["books"] = do
+ toMessageM $ XML (XSL "/static/books.xsl") $ toElement
+ [(Book "Haskell Curry" "Functions" "lambda")
+ ,(Book "Many" "Haskell Report" "String -> IO ()")]
+
+main = stdMain $ simpleHTTP "static/books.xsl" [("/static/", "static")] app :*: End
+
+
++Make a new directory called 'static' and insert the code below into a file called +'static/books.xsl'. This directory has to be at the same place where you run the +program. +
++<?xml version="1.0" encoding="ISO-8859-1"?> +<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> +<xsl:template match="/"> +<html> + <body> + <h2>Books</h2> + <table border="1"> + <tr bgcolor="#C0C0C0"> + <th align="left">Title</th> + <th align="left">Author</th> + </tr> + <xsl:for-each select="Books/Book"> + <tr> + <td><xsl:value-of select="@title"/></td> + <td><xsl:value-of select="@author"/></td> + </tr> + </xsl:for-each> + </table> + </body> +</html> +</xsl:template> +</xsl:stylesheet> ++
+Now you can point your browser at http://localhost:8000/books and you will see +a list of books. Depending on your browser, you will see the XML code or HTML +code when you examine the source of the document. +
++Let's examine this program. +
++module Main where +import HAppS + +data MyState = MyState deriving (Read,Show) + +instance StartState MyState where + startStateM = return $ MyState +instance Serialize MyState where + typeString _ = "MyState" + encodeStringM = defaultEncodeStringM + decodeStringM = defaultDecodeStringM ++
+For this example we use a very minimal state which contains no information. +
+ ++type Books = [Book] +instance ToElement Books where + toElement bs = listElem "Books" [] $ map toElement bs ++
+The type Books is nothing but a list of single books. The derivation of the +class ToElement allows us later on to call the toElement function to get +a XML representation of this book list. +
++The toElement function is written with the listElem function which is +provided from the HAppS.Protocols.MinHaXML module (automatically imported +when you import HAppS). It creates a XML element called "Books" with no +attributes (the empty list). This element contains the XML representation +of the books in the list as child elements. These are generated by +applying the toElement function to the list of books. +
+ +
+data Book = Book {author::String, title::String, content::String}
+instance ToElement Book where
+ toElement b = textElem "Book"
+ [("title", title b)
+ ,("author", author b)] $ content b
+
++The datatype Book defines a book itself. It has an author, a title and +a content. As before with the Books type, it derives from the ToElement +class. +
++Instead of the listElem function we use now textElem. It allows to create +an element that contains text in it's body. Additionally we define two +attributes of this element, title and author. The content of the book +is written as text. +
+ ++app :: Method -> Host -> [String] -> Ev MyState Request Result +app GET _ ["books"] = do + toMessageM $ XML (XSL "/static/books.xsl") $ toElement + [(Book "Haskell Curry" "Functions" "lambda") + ,(Book "Many" "Haskell Report" "String -> IO ()")] ++
+The message to send to the client is constructed by a call to the toElement +function. The XML constructor takes an element and information to the +stylesheet to be used as parameters. In this case, an XSL stylesheet is used. +
++The toMessageM finally converts the XML into a message with header +information that can be sent to the client. It is predefined for XML and some +few other types. You can derive from the ToMessage class for any type you +want. +
++Please note that the XSLT handling can happen on server or on client side. +If for example the content field is very big and you rely on the XSLT to +remove it from the HTML (as it is the case in this example). The whole +content will be transferred to the client if the client supports XSLT. hunk ./doc/tutorial.html 650 -To be Continued +
+main = stdMain $ simpleHTTP "static/books.xsl" [("/static/", "static")] app :*: End
+
++The main function is now extended with an indication to serve static +pages from the 'static' directory under the path "/static/". The +list contains tuples of URL locations to directory location mappings. +
+