So I was thinking today about how far you can go with statically type checked web programs. Yesod uses Hamlet and web-routes, which allow you to statically type check your internal urls and html. What other parts of web applications can you type check? Well there are at least two other language domains that are commonly used in web applications, CSS and javascript. Javascript might be a bit hard for now, but CSS type checking might be possible within hamlet. Has this ever happened to you? you write an awesome css class that clears floats. called "AwesomeClearThing" Now it is time to use it in hamlet %p!class="AwesomClearThing" Recompile + Reload later...nothing has changed...Fail! what you need is: %p!@class|AwesomClearThing@ and now since it is type checked, the compiler will tell you something is up. This also has a prerequisite that yesod knows the css that is being used. Another interesting side note of this is that you could potentially figure out which classes and rules are unused and not put them in the compiled css file. There are other things, but I think type-checked class and id names would be a pretty awesome first step. What do you guys think?