[R6RS] safe and unsafe; declarations

Michael Sperber sperber at informatik.uni-tuebingen.de
Sat Mar 4 08:31:42 EST 2006

William D Clinger <will at ccs.neu.edu> writes:

> My concept is that we pretend unsafe mode does not affect
> how exceptions are raised.
> This is fiction, but it is a useful fiction.  Its chief
> advantage is that we can pretend unsafe mode does not
> conflict with any language in the R6RS that might require
> exceptions to be raised in certain situations.

OK, I think I understand now.  However, I think this is highly
confusing.  Here's one technical reason why:

> There is only one notion of exception, but there are two
> mechanisms for handling exceptions.  One mechanism is the
> one that will be described in the R6RS, which is presumably
> similar to SRFI-34.  The other mechanism is the one used
> in unsafe mode, which the R6RS will not constrain in any
> way whatsoever.

I'm not sure this will really groove with SRFI 34, because raising an
exception is the same thing as invoking the current exception handler.
Therefore saying that unsafe mode might invoke a different handling
mechanism implies that the "raising mechanism" is also different.
(But I think it would be confusing even if we adopted some other
notion of "raise.")

As we'll be sorting out the various exceptional situations in the
report anyway, wouldn't it be preferable to use language saying: "In
safe mode, this will raise an XXX exception; in unsafe mode, the
behavior is unspecified." ?

Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla

More information about the R6RS mailing list