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Marcin 'Qrczak' Kowalczyk <qrczak@xxxxxxxxxx> writes: > I want to make more predictable when the programmer will obtain a > ratnum and when a flonum. And I want him to be sure that he will not > obtain some weird representation like "a ratnum with inexactness bit" > or "fixed-size decimal fraction" without explicitly asking for it. How about providing arithmetic functions that provide those guarantees then? You're approach has been to have programmers ask for a particular *implementation*. This is not the scheme way, and it's a bad way to think about programming in general. Much better is to think about what *features* specifically you want, and have programmers ask for *those*. It is in that sense that I say that Scheme does not have a "flonum". So far you've mentioned one feature: constant size arithmetic. I've suggested one way of having programmers ask for that feature (though there are surely others). >> See, this is where you're wrong. Constant-width addition is valuable >> for integers too, not just floats. But when people doing integer >> arithmetic want that, it's an "efficiency hack", and when you want it >> for floating point, it's Absolutely Essential. > > What do you mean by constant-width addition? I mean "addition in which the space use of the output is no larger than the input". This is a feature which you said was needed for reals (I agree) and it's a feature that is useful for integers too. > Fixed-size floating point arithmetic differs in that it's safe, that > people expect it to be slightly inexact (or should be taught to expect > this), and that often the performance difference between fixed size > floating point and exact ratios is huge, while the difference in the > answer is small. I don't know what you mean by "safe"; there are legions of programmers making bad mistakes because of the unobvious intricacies of the way that floating point simulates well understood mathematical operations. > Of course the programmer can use exact ratios instead if he chooses. > It should be his choice, not the Scheme implementor's choice. But it already is! I'm baffled by what you're asking here; the feature you seem to be requesting (though I can't tell for sure) is now that you want a way for programmers to specify whether they want exact or inexact numbers. Of course, Scheme provides that already. > Letting (+ 1.2 3.4) perform fixed-size binary floating point arithmetic > is compatible with both the existing standard and common practice. What exactly are you asking for? Perhaps I'm misunderstanding. By "letting" do you mean "requiring"? (Because then, you're wrong.)