[Haskell-beginners] happstack versus yesod

Michael Snoyman michael at snoyman.com
Tue Apr 5 20:32:38 CEST 2011

This probably isn't the right forum for expressing this thought, but here
goes anyway:

What exactly is the freedom that Yesod takes away from you? I know this idea
gets passed around a lot: Yesod isn't "really" Haskell, Yesod is its own
language, etc. But all of that is really just talking about some sugar that
Yesod puts in place for you: under the surface, it's just functions, data
types and type classes. You can go ahead and write a complete Yesod
application without using Template Haskell of QuasiQuotation.

So what's the restriction that Yesod has that Happstack/Snap don't? Yesod
requires you to provide some datatypes. That's it. What's the purpose of the
datatypes? Mostly, it's about type-safe URLs. I'm not exactly sure why the
term "restriction" or "freedom" even applies here: Yesod has a *feature*
that Happstack/Snap do not include out of the box.

Let me phrase this in a different way: "But I don't like Haskell, because
the idea of Python in more interesting for me. Python gives you some
freedom." I really do see this as the same argument. You can go ahead and
right some code without static type checking in Python, and you might even
write it faster than you would have in Haskell. But go ahead and start
making changes, and unless you have some very good unit tests, you're in for
a world of hurt. In Haskell, often times the compiler will save you from

The same is true in Yesod. I've refactored incredibly large codebases, with
hundreds of different resource patterns, and *never* had to worry about
404s. Maybe some people consider that giving up freedom. I consider it
giving up the freedom to shoot yourself in the foot.

Oh, and if you are absolutely dependent on the idea of getting rid of this
data-type requirements, and want all the freedom of dynamic routes, you can
try out a 44 line module[1] that I mentioned recently[2].

OK, enough of this rant. I'm not trying to attack you, I'm just tired of
this notion that Yesod is a ball-and-chain around your ankles. People can
have legitimate reasons to prefer Happstack or Snap to Yesod, I've never
claimed that it was a perfect framework for everyone. I just don't think
this is one of those legitimate reasons.


[1] https://gist.github.com/884802

On Tue, Apr 5, 2011 at 8:35 PM, Alexey G <kreed131 at gmail.com> wrote:

> Hello. It's very interesting theme for me and I want to express my
> opinion.
> Yesod - very fast web-framework(
> http://www.yesodweb.com/blog/preliminary-warp-cross-language-benchmarks).
> But I don't like Yesod, because idea of Happstack more interesting for me.
> Happstack gives to you some freedom.
> I trying to use Snap Framework now. And it's very good for me. Try it
> http://snapframework.com/!
> Sorry for my english.
> 2011/4/5 Ramy Abdel-Azim <ramy.abdelazim at gmail.com>
>> I already posted about this a little bit but i think i should let the old
>> thread get back to it's regularly scheduled conversaion. on to my question:
>> So I know there are a million easier ways to createa  blog (wordpress,
>> django, drupal, etc. etc.) but which would you recommend I use to build a
>> beginner website that is simliar to a blog: happstack or yesod?
>> _Ramy
>> _______________________________________________
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