[Haskell-beginners] What's this [f| data |] ??

[Jack Henahan]

parseRoutes is a quasiquoter [1]. It uses a type-safe metaprogramming language called Template Haskell [2] to parse a string as a Route (e.g., HomeR is a Route describing the base resource). You can see the source here [3]. I'm pretty new with Yesod, myself, so I'm sure someone else will give you a more in depth description shortly.

[1]: http://www.haskell.org/haskellwiki/Quasiquotation
[2]: http://www.haskell.org/haskellwiki/Template_Haskell
[3]: http://hackage.haskell.org/packages/archive/yesod-routes/1.0.1.2/doc/html/src/Yesod-Routes-Parse.html#parseRoutes

On Jul 3, 2012, at 10:10 PM, Carlos J. G. Duarte wrote:

> Hi. I'm trying to get into haskell in my free time. I have already covered some syntax, but there's plenty to do yet, and when I'm consulting other people's stuff, I find lots of unknown constructs to me, which turns harder to lookup for, due to the very "symbolic" nature of Haskell.
> 
> For instance, on this http://www.yesodweb.com/blog/2012/04/yesod-js-todo they have a few constructs like this:
> 
> mkYesod "App"
>  [parseRoutes|
> / 
> HomeR GET
> 
> /todo 
> TodosR GET PUT
> 
> /todo/#
> TodoId TodoR GET DELETE
> 
> |]
> 
> 
> It seems that the inline text is going to be fed to parseRoutes. How does that constructs work (links?)? I already know list comprehensions which appear to be related with this. 
> 
> Thanks.
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> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners

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