Hello,
On Fri, 13 Nov 2020 21:51:49 +1100
Steven D'Aprano <st...@pearwood.info> wrote:
> > match foo:
> > case ("foo", >val1):
> > ...
> > case ("bar", >val2):
> > ...
>
> > 1. Much more intuitive for beginners. (If Python adopts it, I see
> > other "user-friendly" languages adopting the same pattern in the
> > coming decades).
>
> I think you and I have a very different concept of "intuitive for
> beginners" here. I don't think that using the *greater than symbol*
> as a sigil for assignment would have been "intuitive" to me as a
> beginner, or anyone I have helped teach over the years.
Treat it as "arrow pointing into a variable identifier, meaning that
value is getting into variable". ">>" and "->" are other alternatives
with the same intuitive connotation. ">>" is a particularly interesting
choice, as it should give warm fuzzy feelings (and partial moral
compensation) to all folks who miss the print statement
('print >>sys.stderr, "foo"').
[]
> > # Why is this possible?
> > obj.foo, obj.bar = val
> >
> > # And this is not?
> > match val:
> > case obj.foo, obj.bar:
>
>
> I agree with this. I think it is surprising that unqualified names
> are binding patterns but qualified names are not. That difference
> gives me pause.
But *that's the problem* we're trying to solve!
Aka, stop resolving binding-vs-value ambiguity by assigning semantic
discrepancies to different *syntactic* patterns, and instead, consider
using *punctuation* to resolve the ambiguity. And then there're 2
choices.
1. Use punctuation ("sigils") to mark as-value terms (expressions).
This is now well (enough) covered in PEP642, from which this thread
is, well, started.
2. Use punctuation ("sigils") to mark as-binding terms. This choice
still seems to be under-considered. (As in: it doesn't seem like many
people, including the PEP authors, tried to say "indeed, what if?"
and feel thru it. I mean, try really hard. I trust the "gang of 4"
spent maybe whole few hours on that and delivered "no" to all us. It's
still not the same as dozens of people trying it over a few months).
> But using `>` as an assignment sigil is surely worse
> than the problem you hope to solve with it.
">" is just a notation mark and one of many possible choices. ">", "->",
">>", "@", "$" were mentioned before, and today, even word-fulls like
"bind" were proposed (thread "Words rather than sigils in Structural
Pattern Matching"). All valid choices to consider, *once* we agree that
it is a viable idea to mark bind-terms, on par with other alternatives,
and not a throw-away "misconception", how PEP635 tries to represent it
(https://www.python.org/dev/peps/pep-0635/#capture-patterns)
--
Best regards,
Paul mailto:pmis...@gmail.com
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