[Ur] Exceptions handling

[Vladimir Shabanov]

2010/8/24 Adam Chlipala <adamc at impredicative.com>:
>> 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.

Hmm. Of course I can check constraint violations.

Interesting is there any way for Ur to force programmer to check
violations (don't allow DML w/o necessary checks)? (but I'm afraid
that it can be more complex than adding exceptions ;).

And there is another way to check DML errors -- another function dml'
can be adder which returns option string instead of error page, e.g.
    result <- dml' (...);
    case result of
          None => return "ok"
          Some e => return strcat("dberror: ", e)