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Re: external representations




On Jun 21, 2005, at 11:18 AM, William D Clinger wrote:

Aubrey Jaffer wrote:

SRFI-70 mandates no connection between IEEE-754 NaN and 0/0.

No one said it did.  In the discussion of SRFI-70,
however, Bradley Lucier proposed having external
representations for NaNs.  I was responding to
Lucier's proposal as much as to yours.

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).

Brad