On 06/23/2020 10:11 PM, Ethan Furman wrote:
As others have noted, the leading dot to disambiguate between a name assignment
and a value check is going to be a problem.
I suspect I wasn't as clear as I could have been, so let me try again (along
with some thinking-out-loud...).
First premise: the visual difference between BLACK and .BLACK is minuscule,
and will trip people up.
Second premise: there is no practical difference between
match color:
case BLACK:
# do stuff
and
match color:
case _:
BLACK = color
# do stuff
Conclusion: there is no need for an always true match, since that's basically the same thing as an
"else" (or "case _", currently).
Since we don't need an always True match, we don't need to allow a single name after
"case" as an assignment target, which means we don't need to support ".name" as
a value target -- the plain name will work as a value target.
Am I just stuck on the single-name scenario and missing the bigger picture?
What happens here:
aught = 0
match an_obj:
case Point(aught, 6):
# do stuff
for the aught in Point to match the global aught it needs the dot prefix,
doesn't it. But this is what guard clauses are for, right?
aught = 0
match an_obj:
case Point(x, 6) if x == aught:
# do stuff
So we still don't need a leading dot.
Going back to the example and taking a different tack [1]:
match color:
case BLACK: # BLACK is the global variable
is really the same as
match color:
case color == BLACK:
We've been dropping the "color ==" part, but what if we only drop the "color"
part?
match color:
case == BLACK: # comparing against the global variable
and then
match color:
case BLACK: # always True match with `color` assigned to `BLACK`
Equal signs are much easier to notice than a single dot.
Okay, I've pretty much done a 180 here -- a bare name should be an assignment target, but instead of
having a leading dot be the "this is really an existing variable switch", have an operator be
that switch: ==, <, >=, etc. Of course "==" will be the most common, so it can be
dropped as well when the meaning doesn't change in its absence (kind of like parentheses usually being
optional).
--
~Ethan~
[1] https://en.wikipedia.org/wiki/Tack_(sailing)
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