April 2012
Intermediate to advanced
294 pages
6h 27m
English
Content preview from Developing Web Applications with Haskell and YesodBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Chapter 3. Basics
The first step with any new technology is getting it to run. The goal of this chapter is to get you started with a simple Yesod application, and cover some of the basic concepts and terminology.
Hello World
Let’s get this book started properly: a simple web page that says Hello World:
{-# LANGUAGE TypeFamilies, QuasiQuotes, MultiParamTypeClasses,TemplateHaskell, OverloadedStrings #-}importYesoddataHelloWorld=HelloWorldmkYesod"HelloWorld"[parseRoutes|/HomeRGET|]instanceYesodHelloWorldgetHomeR::HandlerRepHtmlgetHomeR=defaultLayout[whamlet|HelloWorld!|]main::IO()main=warpDebug3000HelloWorld
If you save that code in helloworld.hs and run it with
runhaskell helloworld.hs, you’ll get a web server
running on port 3000. If you point your browser to http://localhost:3000, you’ll get the following HTML:
<!DOCTYPE html> <html><head><title></title></head><body>Hello World!</body></html>
We’ll refer back to this example through the rest of the chapter.
Routing
Like most modern web frameworks, Yesod follows a front controller pattern. This means that every request to a Yesod application enters at the same point and is routed from there. As a contrast, in systems like PHP and ASP you usually create a number of different files, and the web server automatically directs requests to the relevant file.
In addition, Yesod uses a declarative style for specifying routes. In our example above, this looked like:
mkYesod"HelloWorld"[parseRoutes|/HomeRGET
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.