[Ur] Generalizing transactions

[Karn Kallio]

> Karn Kallio wrote:
> > Adam, now that somebody ( Marc Weber ) is working on an application (
> > payment gateway ) where the transaction model of Ur/Web does not cleanly
> > apply, is there a chance of you generalizing Ur/Web transactions in a
> > safe, principled way ( that allows representing the semantics of the
> > application's effectful operations within Ur/Web )?  For example, I
> > think that the problem of leaving a permanent record of an event ( e.g.
> > receiving an order and not removing it on failure rollback ) could be
> > handled with a SAGA that has a null compensation for the process of
> > writing the record.
> 
> It seems like Marc and I have settled on a very straightforward and
> not-ugly way of implementing what he wants, so this case doesn't seem to
> me like a good impetus to add a new fancy feature.  I'm perfectly happy
> to help you figure out how to implement it yourself, if you want. :-)

Ok :)

Please accept my apologies for sounding snarky or demanding.  I want to be 
clear that I think Ur/Web is an amazing accomplishment and that you are 
breaking important new ground in the "design space" for the coming generation 
of "almost dependently" typed languages.

Also, about impredicative kind polymorphism, I was not complaining, only 
trying to make a joke ... I think that for the intended domain the existing 
implementation of kind unification is fine.  To illustrate that Ur/Web *does* 
exhibit impredicativity at the value/type level ( you have already pointed 
this out, but just to undo any confusion I may have left on this list ) I 
posted an example on the wiki at 
http://www.impredicative.com/wiki/index.php/Impredicativity_in_Ur/Web

Once again, thanks for Ur/Web !