If I'm following this correctly, shouldn't we just say that Duration does Num? That way, a Duration can be used exactly like a Num is (with units measured in seconds); but it could also have special capabilities above and beyond what a Num can do, if such capabilities are needed.
More generally, I wonder if maybe we _should_ provide a tool to help with dimensional analysis: a role that does Num, but also tracks the units for you. The simplest version would leave it up to the programmer to handle unit conversions (e.g., divide a Dimensional that uses the "seconds" unit by a Dimensional that contains 86400 for its value and "seconds/day" for its units to get a Dimensional that uses the "days" unit, rather than providing built-in unit conversion routines). Indeed, th simplest form of Dimensional ought to be able to work with arbitrary units. The idea here isn't to place limitations on anything, but rather to make it easier to track additional data that's relevant to the calculations being performed. With this in place, Duration would be synonymous with "Dimensional, measured in 'seconds'". That said, it's possible that this would open up a can of worms. Would it? If so, it can be postponed; Perl 6 has this nice little versioning ability that lets us retroactively alter roles; so one could easily put together a Dimensionality module at a later date that redefines what a Duration is. -- Jonathan "Dataweaver" Lang
