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Gmane
From: Dimitry Golubovsky <golubovsky <at> gmail.com>
Subject: "Hello World" in Haskell for web browser
Newsgroups: gmane.comp.lang.haskell.cafe
Date: Friday 7th March 2008 03:05:01 UTC (over 9 years ago)
Hi,

I have noticed that some people tried to compile a traditional Haskell
program using IO monad to show "Hello World" using Yhc Web Service.

Thanks for your interest, and here are some clues.

The programming paradigm chosen for Haskell Web programming is not
based on monads. It is based on CPS-style calls to DOM functions by
Haskell code compiled to Javascript. Further on, additional layers may
stack up (such as Haskell Web Toolkit) to provide more convenient
APIs, but DOM is the basis.

So here is an example of "Hello World" program written this way:

-- begin pasteable code --

module HelloWorldDOM where

import CPS
import UnsafeJS
import CDOM.Level2.DomUtils
import DOM.Level2.Dom
import DOM.Level2.Html2
import DOM.Level2.HTMLElement
import DOM.Level2.HTMLDivElement

main = getHTMLDocument $ \doc ->
       documentBody doc $ \body ->
       mkText doc "Hello World" $ \txt ->
       mkDiv doc $ \dv ->
       addChild txt dv $ \_ ->
       addChild dv body $ id

-- end   pasteable code --

The meaning of this:
  * get reference to the HTML document node first (it is the parent of
everything),
  * extract the  tag node, create at text element with "Hello World",
  * create a 
tag node, * insert the text node into div, * insert div into body Or, same in HTML:
Hello World
but filled in dynamically. Using Haskell Web Toolkit API, the same may be expressed in more compact fashion: -- begin pasteable code -- module HelloWorldHsWTK where import DOM.Level2.HTMLDivElement import Graphics.UI.HsWTK main = docBodyC (mkDiv |<< textP "Hello World") -- end pasteable code -- Here, docBodyC is roughly equivalent of the first two DOM calls, mkDiv is same as above, |<< means "insert into container", and textP is a wrapper around mkText. Earlier, I posted the link to Haddock-generated documentation which also includes the Haskell DOM API. Here it is again: http://www.golubovsky.org:5984/_utils/yhcws/index.html Hopefully this example along with the documentation provided helps shed some light on Haskell Web programming techniques. Feel free to ask questions. Thanks. -- Dimitry Golubovsky Anywhere on the Web
 
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