Hi Guido,
On 16/11/2020 4:41 pm, Guido van Rossum wrote:
Thanks Mark, this is a helpful and valuable contribution.
I will try to understand and review it in the coming weeks (there is no
hurry since the decision is up to the next SC) but I encourage you to
just put it in PEP form and check it into the PEP repo.
Because I only skimmed very briefly, I don't have an answer to one
question: does your PEP also define a precise mapping from the PEP 634
syntax to your "desugared" syntax? I think that ought to be part of your
PEP.
No it doesn't define a precise mapping, and I don't think it will.
I'm not familiar enough with ever corner of PEP 634 to do that.
I could add a general "how to" guide though. It fairly straightforward
conceptually but, as you know, the devil is in the details.
Cheers,
Mark.
--Guido
On Mon, Nov 16, 2020 at 6:41 AM Mark Shannon <[email protected]
<mailto:[email protected]>> wrote:
Hi everyone,
There has been much discussion on the syntax of pattern matching for
Python (in case you hadn't noticed ;)
Unfortunately the semantics seem to have been somewhat overlooked.
What pattern matching actually does seems at least as important as the
syntax.
I believe that a pattern matching implementation must have the
following
properties:
* The semantics must be precisely defined.
* It must be implemented efficiently.
* Failed matches must not pollute the enclosing namespace.
* Objects should be able determine which patterns they match.
* It should be able to handle erroneous patterns, beyond just syntax
errors.
PEP 634 and PEP 642 don't have *any* of these properties.
I've written up a document to specify a possible semantics of pattern
matching for Python that has the above properties, and includes reasons
why they are necessary.
https://github.com/markshannon/pattern-matching/blob/master/precise_semantics.rst
It's in the format of a PEP, but it isn't a complete PEP as it lacks
surface syntax.
Please, let me know what you think.
Cheers,
Mark.
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--
--Guido van Rossum (python.org/~guido <http://python.org/~guido>)
/Pronouns: he/him //(why is my pronoun here?)/
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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