Re: feature request from r5rs

On Wed, Jun 11, 2003 at 09:27:06AM -0400, Narang wrote:
> 1st caveat I agree with but the other two caveats are also true for
> 
> (+ (force (delay (* 3 7)) 13)      ===> 34

Oh right, as for efficiency, if it was supported by the compiler, and 
introduced as a new uexp, it shouldn't affect performance anywhere else.

	Scott

> 
> Matthias Radestock <[email protected]> writes:
> 
> > Narang wrote:
> > > From r5rs: * Some implementations may implement ``implicit forcing,''
> > > where the value of a promise is forced by primitive procedures like
> > > cdr and +:
> > > (+ (delay (* 3 7)) 13)          ===>  34
> > > Can this feature be added to sisc? thoughts.
> > 
> > It wouldn't be hard to add, with three caveats:
> > 
> > * preventing it from slowing down *everything* is difficult,
> > 
> > * synchronization is required in order to implement the correct
> > semantics in the presence of multiple threads,
> > 
> > * care needs to be taken to ensure the correct call/cc semantics is
> > implemented.
> > 
> > R5RS doesn't say anything explictly about the last point. However, it
> > is clear from the examples that capturing a k inside a delayed
> > expression and subsequently invoking it will
> > 
> > * (partially) re-evaluate the delayed expression and re-set the
> > memoized value,
> > 
> > * resume computation at the point where the force (explicit or
> > implicit) occured.
> > 
> > 
> > Matthias.
> 
> 
> 
> -------------------------------------------------------
> This SF.net email is sponsored by:  Etnus, makers of TotalView, The best
> thread debugger on the planet. Designed with thread debugging features
> you've never dreamed of, try TotalView 6 free at www.etnus.com.
> _______________________________________________
> SISC-devel mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/sisc-devel
> 

--

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.2 (GNU/Linux)

iD8DBQE+5zoHr9IW4v3mHtQRAqqTAJwO2Trxny5V9UBwKdPKa5TuMhw33wCaArfg
u7uxcQX2koSnkX0Y1s47YUU=
=+z9e
-----END PGP SIGNATURE-----