Michael Montague scripsit:

> I think this is the issue for Kawa: If all of the clause tests evaluate
> to false and the 'guard' has no 'else' clause, then 'raise-continuable'
> is invoked on the raised object within the dynamic environment of
> the original call to 'raise' or 'raise-continuable'. But the 'guard'
> clauses are evaluated with the dynamic environment of the 'guard'. If
> you use an upward continuation to get to the dynamic environment of
> the 'guard', then you can't get back to the continuation of 'raise'
> for the implicit 'else' case.

That's right as far as it goes.  The trouble is that we want guards and
exception handlers to be able to intercept exceptions thrown in Java code
as non-continuable Scheme exceptions.  That's why the convolutions
described in my original message are desirable.

For implementations like SISC, where the Scheme stack is not the Java
stack, there isn't a problem.

--
I am expressing my opinion.  When my            John Cowan
honorable and gallant friend is called,         cowan@ccil.org
he will express his opinion.  This is           http://www.ccil.org/~cowan
the process which we call Debate.                   --Winston Churchill

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