Should we consider making in-range signal an error for floats? I guess backwards compatibility says "no" but maybe in a future racket? With a note in the error message that points people in the right direction?<div> </div><div>Robby On Friday, February 27, 2015, Konrad Hinsen <<a href="mailto:konrad.hinsen@fastmail.net">konrad.hinsen@fastmail.net</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On 26/02/2015 15:13, Neil Toronto wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> The second alternative is a little harder to get right because of fencepost errors [1]. Fortunately, Racket has a library function for it. Unfortunately, it's buried in `plot/utils`. Here it is in action: > (require (only-in plot/utils linear-seq)) > (linear-seq 0.0 1.0 4) '(0.0 0.3333333333333333 0.6666666666666666 1.0) </blockquote> That's the best solution in my opinion. <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> I should really move this function into `math/base`. </blockquote> Yes! <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> If you must use a flonum step size, do something like this: (define (flonum-range start end step) (define n (exact-ceiling (/ (- end start) step))) (for/list ([i (in-range 0 n)]) (+ start (* i step)))) To get points with 0.5 ulp error each, which is the best you can do, add (require math/flonum) to your program and change the loop body to (flfma step (fl i) start). Arguably, `in-range` should do something like the above when given floating-point step lengths. I don't know how feasible that is, though. </blockquote> It would obviously break backward compatibility. And it would complicate the rather simple mental model one can have of in-range. More fundamentally, I am not sure it would be much of an advantage. Think of the two kinds of users: 1) Those who are not aware of the problem. They will still fall into the trap, only a bit later, and the cause of the problem will be even more hidden. It's a bit like languages that do decimal rounding of float output. 2) Those who are aware of the problem. They would use linear-seq, but might prefer the modified in-range in specific situations for compactness. I suspect group 1) is the bigger one, so the most important measure is to promote linear-seq instead of in-range for floats. Konrad. ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </blockquote></div>