[web-devel] WAI Routing

Stephen Paul Weber singpolyma at singpolyma.net
Thu Aug 9 05:25:26 CEST 2012

I'm back!  I've walked in the desert for a bit longer than last time I was 
on this list, and have a much better handle on Haskell base concepts, which 
is useful.

So, I re-looked-at yesod-routes as it exists now, and Yesod.Routes.Dispatch 
is very nice for doing the sort of thing I want.  Doesn't even use any 
language extensions itself!  (Oh, almost, it uses bang patterns.  Or is that 
not an extension when used in a datatype?  Anyway...)

Unfortunately, using Yesod.Routes.Dispatch by itself is a bit verbose.  Of 
course, yesod-routes has all kinds of nice utilities to help with that, but 
they are very TH-heavy, so I set out to build a different way: code 

The result is: <http://hackage.haskell.org/package/route-generator> which 
takes in a simple text file format (attoparsec FTW!) and outputs a module 
that can be compiled into any application using yesod-routes and provide 
a list of routes based on the text file.  The types of the captured URI 
segments are inferred from the types of the actual Haskell code that handles 
the route.

The generator assumes a single module that it will import exports names for 
all of the handlers, but I don't think this is too bad since you can always 
have a module that just re-exports all the handlers from wherever you define 

A simple example is in the git repository.

I have also pushed up <http://hackage.haskell.org/package/wai-dispatch>, 
which is a simple wrapper around Yesod.Routes.Dispatch for use in WAI apps 
to convert a "default" (likely 404 or static file serving) Application, and 
a list of Route for yesod-route, into an Application that does the routing.  
It's very little code, but I immidiately identified it as code that would 
end up appearing in every single one of my web apps, so I abstracted it out 
into a tiny library.

Stephen Paul Weber, @singpolyma
See <http://singpolyma.net> for how I prefer to be contacted
edition right joseph
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