Per Bothner scripsit: > 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 don't think such support is required in the general case. The real numbers and the complex numbers with exact 0 as the imaginary part can be identified. Of my usual suite of Schemes, only SISC fails to make them the same in the sense of EQV?. > 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? Sqrt is free to return inexact results on exact arguments, and a mixed-exactness number is inexact (in the sense that INEXACT? answers #t to it). > (sqrt -5) ==> 0.0+2.23606797749979i That works for the same reason that (sqrt 4) may return 2.0. > (sqrt -inf.0) ==> +inf.0i > i.e. with an exact real part. That is also licit. -- John Cowan co...@ccil.org http://ccil.org/~cowan The competent programmer is fully aware of the strictly limited size of his own skull; therefore he approaches the programming task in full humility, and among other things he avoids clever tricks like the plague. --Edsger Dijkstra _______________________________________________ r6rs-discuss mailing list r6rs-discuss@lists.r6rs.org http://lists.r6rs.org/cgi-bin/mailman/listinfo/r6rs-discuss
