Re: [Scheme-reports] Formal Comment: R7RS 'eqv?' cannot be used for reliable memoization

[Ray Dillinger <bear@x>]

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I see +0.0 and -0.0 as branch cut selectors.

Both are numerically zero, but distinguished by which
branch cut we want to talk about when we ask about the
result of some expressions not continuous at zero.

Branch cut selectors are strictly unnecessary in a
language that has the ability to return multiple values
from a function; the alternative is to simply return
both (or all) answers at non-continuous points.  But
to take full advantage of this we'd need multivalent
variables too.

I'm not advocating removing -0 from R7; it's still
useful in implementing convenient (single-return)
math functions and getting the primary return value
to be the one people actually want.  I'm just
pointing out that it isn't strictly necessary.

				Bear
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