[Ur] Building site templates

[Adam Chlipala]

austin seipp wrote:
> As for the inference errors: they are bad, but they generally point
> you around the code at fault as they did here, if you go by the error
> line #s and look around. You'll get intuition for the actual errors
> (in all their verbosity) as you keep going forward. The compiler does
> tricky things for its unification algorithm to work in the presence of
> the powerful Ur type system, so sometimes the inferred types can seem
> confusing as an example.
>    

I just want to add that I think the messages below are just fine! :)  
You have to understand the Ur type system to use Ur/Web, and the first 
error message explains the problem quite directly.  The following error 
messages wind up being fairly nonsensical, because the first error 
injects an ill-kinded constructor.

It is my intention that the official Ur/Web tutorial:
     http://www.impredicative.com/ur/tutorial/
explains all the context needed to understand these error messages.  If 
that's not the case, specific suggestions will be appreciated!

> On Tue, Dec 6, 2011 at 3:33 PM, James Parker<jp at jamesparker.me>  wrote:
>    
>> I've tried xml, body, and xhtml. Is there some other type I can try? If I simply define sidebar inside template, the project will compile and run correctly.
>>
>> The source is available here if it's helpful:
>>
>> https://github.com/jprider63/UMDTalks
>>
>> Here's the full error message:
>>
>> /home/james/Projects/UMDTalks/common.urs:4:32-4:35: Wrong kind
>> Constructor:  Basis.xml
>>   Have kind:  {Unit} ->  {Type} ->  {Type} ->  Type
>>   Need kind:  Type
>> Incompatible kinds
>> Kind 1:  {Unit} ->  {Type} ->  {Type} ->  Type
>> Kind 2:  Type
>>