Darren Duncan wrote: > I don't know if this was previously discussed and dismissed but ... > > Inspired by some recent discussion in the "comparing inexact values" thread > plus some temporal discussion and some older thoughts ... > > I was thinking that Perl 6 ought to have a generic interval type that is > conceptually like Range, in that it is defined using a pair of values of an > ordered type and includes all the values between those, but unlike Range > that type is not expected to have discrete consecutive values that can be > iterated over.
Note that smart-matching currently treats Range as an interval. The question is whether we need intervals for any other purpose. If we do, perhaps we could still press Range into service, but indicate that there are no discrete consecutive values by saying something like ":step(0)" (where "0" is being used to mean "arbitrarily small" rather than truly zero). This would disable some uses (such as using it as a looping mechanism or counting the number of items that it encompasses), but might enable some others. > I'm thinking of a Range-alike that one could use with Rat|Num or Instant > etc, and not just Int etc. There would be operators to test membership of a > value in the interval, and set-like operators to compare or combine > intervals, such as is_inside, is_subset, is_overlap, union, intersection, > etc. Such an interval would be what you use for inexact matching and would > be the result of a ± infix operator or % postfix operator. Also, as Range > has a .. constructor, this other type should have something. (Not postfix:<%>, please; that should produce a single value by itself.) Instead of saying "set-like operators", etc., why not just say that Interval does Set? The conceptual difference would be that it is a set of continuous values rather than a set of discrete values... This should also allow you to do things like "any($i)" (where $i is an Interval). Indeed, a Set membership test strikes me as being equivalent to smart-matching an any-junction of the Set. As for a constructor: as hinted above, ".." could probably pull double-duty as a constructor for both Ranges and Intervals, based on the spacing (or absence thereof) between members. One _might_ even go so far as to say that :step (or whatever it's called) defaults to 1 for discrete types (such as Int) and to 0 for continuous types (such as Rat); so "0 .. 1" and "0.0 .. 1.0 :step(1)" would each create a two-item Range, while "0 .. 1 :step(0)" and "0.0 .. 1.0" would each create an Interval. -- Jonathan "Dataweaver" Lang
