[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: external representations



Bradley Lucier wrote:

 > Re: Your idea of representing common Scheme values as NaNs.
 >
 > I believe it is possible under IEEE 754 that the "hardware"
 > could return a different NaN for each execution of (/ 0. 0.)
 > in the code (for example). (Some proposals have suggested
 > putting the address of the code and/or a rough time stamp
 > in the mantissa.) I'm a bit concerned that a floating-point
 > operation could return a value that would be interpreted by
 > your scheme as #\C (for example).

Interesting.  Can you tell me of any hardware that actually
does this?

The idea is important even if it only works on some hardware.

Furthermore the idea can be made to work despite hardware that
puts the current PC into the code.  Hardware that puts a time
stamp into the code might be a little harder to deal with,
although the garbage collector should be able to relocate the
heap as necessary to avoid address space that could be confused
with the current time.  No, I am not kidding.

Will