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| Date: Fri, 21 Oct 2005 11:59:06 -0400 | From: "John.Cowan" <jcowan@xxxxxxxxxxxxxxxxx> | | Aubrey Jaffer scripsit: | | > For an interpreter this would mean that 1/2 read before the | > full-tower module was loaded could be an inexact 0.5; but after | > loading 1/2 would read as an exact 1/2. Unpredictability is bad. | | It would merely mean that 1/2 would be an error (and preferably | would signal an error as well). Of course, #e1/2 would still be an | inexact 0.5. I think you meant #i1/2 | > None of the examples in SRFI-77 return -0.0 unless they are | > passed -0.0 as an argument. Does -0.0 result only from a literal | > -0.0 constant? | > | > In an implementation with -0.0, what is the result of (* -5.0 0.0)? | > | > -0.0 is insufficiently specified by SRFI-77; it will be a portability | > killer. | | The IEEE standard is our friend here. 0.0 being the most common inexact number, SCM has only one boxed 0.0. Thus in SCM: (/ (* 0.0 -5.0)) ==> +inf.0 While in an implementation with two zeros: (/ (* 0.0 -5.0)) ==> -inf.0 Thus dual zero systems behave differently from single zero systems, which can cause portability problems.