On Sat, 5 Jun 2004, Phil Steitz wrote:
> The problem is that we do not know what the "working programmers" are
> going to use this class for. Your view seems to be that "Fraction" should
> really be "RationalNumber" -- so that two equivalent fractions are equal.
Yes. Scheme has had this numeric class for a long time and it IS what
"working programmers" find useful.
> The problem is that the class is not named or currently implemented that
> way (in terms of representation and identity). Representing the fractions
> themselves instead of collapsing immediately to the equivalence classes
> (rational numbers) is more flexible; though as you point out, more care
> has to be taken to prevent overflows and some efficiency in the arithmetic
> operations may be sacrificed as a result.
and the current implementation allows both uses, although it deprecates
the latter (due to its being harder for programmers to use correctly).
It can be un-deprecated at some later time if there is outcry.
> If we just fix the computational bugs in the current implementation, the
> overflow situation should be OK with the arithmetic operations implemented
> as they are now, since they call reduce() before returning results. We
> may in fact want to add alternative methods that do not reduce returned
> fractions, or that otherwise restrict / control denominators. While I do
> not have specific use cases in mind, it could be that some
> number-theoretic applications for this sort of thing may exist.
This is always a really bad way to design software.
> The fact that all current operations reduce returned values led me
> initially to agree that it was pointless to maintain the disctinction
> between equivalent fractions. Thinking about it some more, I am -0 to
> changing Fraction to "RationalNumber." I think our best path is to start
> by fixing the computational bugs and then see what sorts of applications
> emerge.
I have an application, and I made the changes that decades of scheme
experience have shown to be useful.
--scott
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( http://cscott.net/ )
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