R6RS seems to require support for "mixed-exactness"
complex numbers. I.e. numbers where the real part is exact
while the imaginary part of inexact or vice versa.
That is implied by these examples for real?:
(real? -2.5+0.0i) ==> #f
(real? -2.5+0i) ==> #t
I.e. -2.5+0i is equivalent to -2.5 and has an exact zero
imaginary part.
So logically a pure imaginary value has an exact zero real part.
So what does the square root of a negative real return?
Is the real part exact zero or inexact zero? The examples
seem inconsistent:
(sqrt -5) ==> 0.0+2.23606797749979i
i.e. with an inexact real part. However:
(sqrt -inf.0) ==> +inf.0i
i.e. with an exact real part.
It seems the following should yield the same answer:
(exact? (real-part (sqrt -5)))
(exact? (real-part (sqrt -inf.0)))
Logically, both should return #t, but R6RS implies #f
for the former and #t for the latter.
Is it (intended to be) implementation-dependent?
I didn't see this covered in the R6RS errata.
--
--Per Bothner
[email protected] http://per.bothner.com/
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