The State of Exceptions (corrected)

Allen Wirfs-Brock Allen_Wirfs-Brock at
Tue Oct 20 04:45:17 UTC 1998

Oops, there was one more thing I forget to mention.  You also need to copy
the current activation stack at the time the continuation is created and
reinstall a copy of this stack when the continuation is evaluated.  Not
pretty, but it worked.

Allen Wirfs-Brock

At 08:59 PM 10/19/98 -0700, Allen Wirfs-Brock wrote:
>At 12:30 PM 10/19/98 -0400, Vassili Bykov wrote:
>>Ralph E. Johnson wrote:
>>> A block with a return in it is what I was thinking of
>>> as a continuation.  A block is a first-class object.
>>Sheldon probably means unlimited extent continuations as in Scheme.  A while
>>ago, I posted a longish message on c.l.s. about imitating continuations
>>using thisContext, it should be at
>><>.  In a nutshell, you can
>>come fairly close remaining at the image level.  ...
>Many years ago I built an experimental image level implementation of
>continuations using the Tektronix version of Smalltalk-80.  It was quite
>straight forward.  Points to consider:
>	a block of the form [:x| ^x] is almost a continuation. ST-80 problems are:
>		x is not local to the block.
>		multiple returns are not allowed so:
>	1) encapsulate the block in another object.  That object serves as the
>continuation object
>	2) when the continuatiuon object is "evaluated" (via a message) do the
>		a) make a copy of the encapsulated block
>		b) do a fixTemps on the copy
>		c) send value: to the copy
>The copy and fixTemps took care of the short comings of the contexts and I
>was able to
>to all the classic scheme style continuation tricks.
>Allen Wirfs-Brock

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