Here's my proposal for how to handle dimensionality in Perl 6: Create a "units" trait that is designed to attach to any Numeric object. Dimensional information gets stored as a baggy object - that is, something that works just like a Bag, except that the count can go negative. (I don't know if the count should be a signed integer or a Num; what happens in dimensional analysis when you try to take the square root of two inches?) Overload the Numeric operators to properly track the units as well as performing their normal activities. Add one or two methods that allow you to easily extract the raw number and/or the units.
For now, unit conversions are always handled manually, and the units themselves are completely arbitrary At some later date we might consider adding a robust database of units and conversion rates; but that's a complication that we needn't deal with up front. Indeed, it might work best as a module to be included by those who want the added tools. Regardless, such a module should not interfere in the ability to use made-up units on the fly; instead, it should provide additional details for units that have been properly registered (such as what kind of value is being measured, which measurement system it's a part of, what the conversion rates are, and what synonyms exist for it). The goal should be to enhance, not restrict. If this is implemented, Duration should be an alias for something to the effect of "Num but units<second>". Otherwise, Instant and Duration remain unchanged. Thoughts? -- Jonathan "Dataweaver" Lang
