Rhodri James wrote:

Eric Nieuwland wrote:

...

Just after I hit ‘send’ it dawned on me it might be preferable to make that

match poly: p0 = Point(x0, y0) p1 = Point(x1, y1) p2 = Point(x2, y2) case Polygon(p0, p1, p2): …

so the part preceded by ‘match’ is the preparation phase for matching.

Are you intending p0, p1 and p2 to be subpatterns rather than object instantiations? That makes me a little twitchy; the difference between what you wrote and:

match poly: p0 = Point(x0, y0) p1 = Point(x1, y1) case Polygon(p0, p1, p2): ... is very easy to miss.

You are perfectly right. That is why I prefer explicit marking of variables to be bound by matching. Your example could then become:

match poly: p0 = Point(x0, \y0) p1 = Point(\x1, y1) case Polygon(p0, p1, \p2): …

and IMHO it would be very clear what to expect.

An alternative would be to ‘declare’ variables that are to be bound to make things even more explicit, like:

match poly: x1 = to_be_bound_by_matching y0 = to_be_bound_by_matching p2 = to_be_bound_by_matching p0 = Point(x0, y0) p1 = Point(x1, y1) case Polygon(p0, p1, p2): …

where a better name than ‘to_be_bound_by_matching’ would certainly be needed.

—eric