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 mailto:mark@hotpy.org> 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_semantic...
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. _______________________________________________ Python-Dev mailing list -- python-dev@python.org mailto:python-dev@python.org To unsubscribe send an email to python-dev-leave@python.org mailto:python-dev-leave@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/BTPODVYL... Code of Conduct: http://python.org/psf/codeofconduct/
-- --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-c...