Announcing Yesod 1.0

April 9, 2012

3 years of development. 80 packages. Dozens of contributors. Thousands of commits.

The Yesod team is very pleased to announce the release of Yesod 1.0. As expected, this was a minor incremental upgrade over version 0.10. You can see a full changelog on the Wiki. The only possibly confusing change I'm aware of is the meaning of approot versus host in the config file; please see the changelog for more details.

We're very proud of this release. With 1.0, we're signaling that we've achieved feature maturity with an API we're happy with. We aren't stopping of course; we already have plans for the next wave of features, mostly focusing on better client side integration. But we consider 1.0 a strong foundation to build on top of.

The rest of this post is intended as an introduction to Yesod for new users.

Introductory Screencast

Yesod 1.0 Introductory Screencast from Michael Snoyman on Vimeo.

Why another web framework?

The main goal of Yesod is to provide robustness. We want a web framework that helps you build secure sites and minimize production bugs. In this endeavor, we follow the mantra that the compiler is your ally, not your enemy. To make this happen, we use Haskell's strong typing to eliminate entire classes of bugs and security holes. This applies to everything from creating valid links (type-safe URLs), avoiding Cross Site Scriping (XSS) attacks, and automatic data marshaling.

Those familiar with more commonly used statically typed languages, like Java or C++, may have already decided that the extra safety is not worth it. Two complaints from traditionaly statically typed languages are:

  • They're just so verbose!
  • I haven't written a single bug that would have been caught by a compiler.

We believe Haskell solves both of these complaints. Due to type inference, you rarely have to give a type signature in your Haskell code. Many of us choose to anyway, and consider it a form of documentation which is enforced by the compiler. But in most cases it's optional.

As for the second point: it's true that the type systems in Java and C++ make it difficult to express program invariants well. In Haskell, however, the expressive type system let's us do much more. If you've ever had an XSS vulnerability, generated an invalid link, treated a stream of bytes as text, or just made a typo, the compiler can help you. This means that in Haskell, you don't have to waste time writing unit tests for the boring, mundane stuff. Let the compiler handle it for you automatically, and you can worry about the more important issues.

The result: Yesod is a web framework with a level of productivity rivaling Rails or Django, but with greater security and much easier code maintenance.

The other advantages

While robustness was our main goal in creating Yesod, we've also achieved other major benefits as well:

  • Asynchronous made easy. Everyone keeps talking about how important asynchronous programming is for creating servers. In other systems, you have to restructure your code to work with callbacks. Haskell's multithreaded runtime does all the heavy lifting for you. You write simple code that asks for data and sends it, and Haskell's compiler (GHC) will restructure it to use the appropriate event library for your OS. This allowed us to write a powerful and fast webserver in about 500 lines of code.
  • Scalable and performant. Yesod lets you write simple, high-level code, and gives you good performance. But when you need more, you can tune your compiled code for something even faster. Many of Yesod’s base libraries work exactly this way: providing a nice, safe interface for users while getting near-C performance with direct memory access. The GHC compiler ensures we get fast machine code at the end of the day.
  • Light-weight syntax. A lot of web development is boilerplate. Setting up routing tables, creating database schemas, and dealing with forms can all be long, repetitive code. Yesod’s has simple DSLs for templating, persistence, routing, and much more. But more importantly the DSLs are correct: they are all compile-time checked to get rid of the runtime bugs.

Learn more

We'll be coming out with a few more introductory blog posts over the next few weeks, and hopefully a few more screencasts too. If you're ready to jump in, the getting started guide gives you all the information you need to get up-and-running with Yesod, as well as a number of handy links. If you want a third-party opinion on what makes Yesod great, check out Yesod excellent ideas.

And later this month, O'Reilly will be publishing our first book on Yesod. You can already read it online.

We're very happy with Yesod, and think it can be a valuable tool for many web developers. We hope you do too!


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