[Ur] constructor-level constraints and more

[Adam Chlipala]

Possibly this point should go in the Ur/Web FAQ. ;)

On 09/26/2013 12:30 PM, Sergey Mironov wrote:
> My plan was to add a shorthand for
> `record (dpage (t ++ [JQ = url]))' like this:
>
> con my = fn t =>  record (dpage (t++[JQ=url]))
>    

The Ur type system doesn't support this sort of abstraction.  The 
recommended approach is to avoid introducing an abbreviation.