In 2016, I wrote PEP 511 "API for code transformers" which proposed a different implementation but also used "preprocessor" use case in the rationale:
""" A preprocessor can be easily implemented with an AST transformer. A preprocessor has various and different usages.
* Remove debug code like assertions and logs to make the code faster to run it for production. * Tail-call Optimization * Add profiling code * Lazy evaluation: see lazy_python (bytecode transformer) and lazy macro of MacroPy (AST transformer) * Change dictionary literals into collection.OrderedDict instances * Declare constants: see @asconstants of codetransformer * Domain Specific Language (DSL) like SQL queries. The Python language itself doesn't need to be modified. Previous attempts to implement DSL for SQL like PEP 335 - Overloadable Boolean Operators was rejected. * Pattern Matching of functional languages * String Interpolation, but PEP 498 -- Literal String Interpolation was merged into Python 3.6.
MacroPy has a long list of examples and use cases.
This PEP does not add any new code transformer. Using a code transformer will require an external module and to register it manually. """ https://www.python.org/dev/peps/pep-0511/#usage-2-preprocessor
I rejected my PEP, extract of the rejection notice:
""" This PEP was seen as blessing new Python-like programming languages which are close but incompatible with the regular Python language. It was decided to not promote syntaxes incompatible with Python.
This PEP was also seen as a nice tool to experiment new Python features, but it is already possible to experiment them without the PEP, only with importlib hooks. If a feature becomes useful, it should be directly part of Python, instead of depending on an third party Python module. """ https://www.python.org/dev/peps/pep-0511/#rejection-notice
Le mar. 15 sept. 2020 à 21:27, Mark Shannon email@example.com a écrit :
I'd like to propose a new PEP for hygienic macros.
I'm attempting to reduce the controversy and pain of adding new syntax to Python, ... by adding new syntax.
That might sound silly, but I hope to persuade that it isn't.
Adding a new feature to the language is always controversial.
Before a new module or functionality is added to the standard library, it must usually prove itself as a package on PyPI.
(Not always the same package, the value of dataclasses was demonstrated by "attrs".)
However, this isn't currently possible with new language features.
Any new language feature has pros and cons. It adds expressive power for some (usually experienced) users, but potentially confuses and inconveniences other users (especially beginners). However, it is very hard, if not impossible, to determine whether adding new syntax will be be beneficial or harmful before the syntax is added.
Is there a way to add new syntax in a way that allows it be battle tested before adding to the released version of the language? Yes there is, Macros.
I'm not talking about C-style macros which do textual substitution, but "hygienic" macros that rewrite the AST during compilation.
Macros allow domain specific new syntactic features, without bloating the language or confusing newcomers.
In general, I would except macros to be used within libraries, so that those libraries gain the power of their custom macros without making Python ever larger and more complex.
However, there is no reason why they cannot be made more widely available. Should a macro become widely used and popular, then it can be considered for adoption into the language.
Cheers, Mark. _______________________________________________ Python-Dev mailing list -- firstname.lastname@example.org To unsubscribe send an email to email@example.com https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://firstname.lastname@example.org/message/7BX4S6RO... Code of Conduct: http://python.org/psf/codeofconduct/