do...until wisdom needed...

[Ben Hutchings]

Graham Hughes <ghughes at lynda.com> writes:
<snip>
> I couldn't even write a RC4 stream encryptor in R5RS, because it
> didn't have a logical xor operation.

Oh, please.  Any logical expression can be written with only nand
operators or only nor operators.  Multiple logical operators are just
syntactic sugar; also, they provide too many ways to do the same
thing.

    A xor B = (A or B) and not (A and B)

            = not (A nor B) and not (not A nor not B)
            = (A nor B) nor ((A nor A) nor (B nor B))

            = not ((not A nand not B) nand (A nand B))
            = (((A nand A) nand (B nand B)) nand (A nand B))
              nand (((A nand A) nand (B nand B)) nand (A nand B))

-- 
Any opinions expressed are my own and not necessarily those of Roundpoint.