Re: exception systems

[Matthias Blume <blume@cs.Princeton.EDU>]

From: "Guillermo J. Rozas" <gjr@martigny.ai.mit.edu>
Subject: Re: exception systems
Date: Fri, 19 Apr 96 12:03:53 -0400

> Even in SML you have to re-instate the exception register, and perhaps
> (I don't know much about SML exceptions), do something else on top.

You don't have to do something else `on top', and restoring a register
is not a big deal at all -- there are other registers to be restored
already anyway.

> Yes, but if you happen to use a library (e.g. basic I/O) that uses
> dynamic-wind unbeknownst to you, you will get in trouble.

Which is why I said I would like to see dynamic-wind go and never come
back.

> |   This is a myth.  SML/NJ's implementation strategy happens to allow a
> |   very cheap implementation of call/cc.  It was, however, not chosen
> |   just because of that.  Also, I don't know what you mean by `making
> |   everything else somewhat more expensive'.  Admittedly, it is a
> |   controversial topic, but if you look at Appel and Shao's papers on
> |   this issue then you will see that the jury is still out.
> 
> We can discuss this ad infinitum, but it is not a myth.

Then, please, be specific.  What is slowed down by SML/NJ's call/cc
mechanism?

-Matthias