On 11 Jul 2020, at 21:03, Eric Nieuwland <eric.nieuwl...@gmail.com> wrote:
> What I meant to say is that as I read the current PEP text there would be a
> confusing difference between
>
> match poly:
> case Polygon(Point(x0, y0), Point(x1, y1), Point(x2, y2)):
> ...
>
> and
>
> p0 = Point(x0, y0)
> p1 = Point(x1, y1)
> p2 = Point(x2, y2)
> match poly:
> case Polygon(p0, p1, p2):
> ...
>
> This would be especially clumsy if I need to match parts in a deep structure.
> It would require me to either write the whole construction as part of the
> ‘match’ or use ‘match’ nested to drill down to the parts I need.
>
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.
This could also resolve the discussion on indentation of the ‘case’ parts and
the placement of the default matching:
match <expression> [as <var>]:
<preparation statements>
case <pattern> [<guard>]:
<statements>
…
[else:
<statements>]
within the preparation statements it would then be allowed to use undefined
variables as receivers of matched parts.
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