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Re: meta-comment on typing

This page is part of the web mail archives of SRFI 77 from before July 7th, 2015. The new archives for SRFI 77 contain all messages, not just those from before July 7th, 2015.

bear wrote:
For example, if I know that I added something to 27 and got -32,
reversibility means I should be able to uniquely determine what was
added to 27; under the rules of linear addition, it would have to be
-59, not any positive number.  But with modular addition, it could be
either of two numbers, -59 and ($MODULUS - 59), so modular addition
isn't reversible like linear additon.

Yeah, but if you have the additional information that all "numbers" are in the range -2^31 to 2^31-1 inclusive, you can determine the unique value that was added to 27 to give -59.

I'm not saying fixnums are great, just that your example doesn't convince me that addition of fixnums is not reversible.


Dr Alan Watson
Centro de Radioastronomía y Astrofísica
Universidad Astronómico Nacional de México