[Ur] Exceptions handling

[Adam Chlipala]

Vladimir Shabanov wrote:
> 2010/8/24 Adam Chlipala<adamc at impredicative.com>:
>    
>> Vladimir Shabanov wrote:
>>      
>>> Ur/Web can throw error on invalid DML (for example "ERROR: duplicate
>>> key value violates unique constraint ..."). Currently this error
>>> results in invalid page.
>>>
>>> Is there a way to handle such errors?
>>>
>>>        
>> No, there is no support for that right now.  Do you have a suggestion of
>> what support you would like to see?
>>      
> There are several ways to add exceptions.
>    

This is certainly a thorough list of ways of supporting general 
exception-handling, but I had hoped (and continue to hope) Ur wouldn't 
need any such facility. ;)

Why can't you just check for uniqueness constraint violations in your 
code before inserting into the database?  I can see the case for a 
simple facility for specifying an alternate error-reporting page, but 
more than that doesn't seem worthwhile.  These errors should only come 
up in buggy programs.