How about instead of omitting the body, it contains a single expression,
say:
def int(x: float): -> float
typing.Prototype
It doesn’t totally break protocol to have a function complie differently
depending on its content— that’s done with generator functions.
-CHB
On Thu, Dec 23, 2021 at 7:20 AM <asleep.c...@gmail.com> wrote:
> Hello
>
> In thread about PEP 677, I (with the help of another proposal) came up
> with an alternative to typing.Callable called function prototypes. The
> basic concept is to create a function prototype object when the body of a
> function is omitted.
>
> The thread can be found here:
> https://mail.python.org/archives/list/python-dev@python.org/thread/OGACYN2X7RX2GHAUP2AKRPT6DP432VCN/
>
> Mark Shannon initially proposed that functions be used as types and
> provided this example:
>
> @Callable
> def IntToIntFunc(a:int)->int:
> pass
>
> def flat_map(
> l: list[int],
> func: IntToIntFunc
> ) -> list[int]:
> ....
>
> I further proposed that we make the body of a function non-mandatory and
> create a function prototype if it is omitted. I provided these examples:
>
> import typing
>
> @typing.Callable
> def IntToIntFunc(a: int) -> int
>
> def flat_map(
> l: list[int],
> func: IntToIntFunc
> ) -> list[int]:
> ...
>
> import ctypes
>
> @ctypes.CFUNCTYPE
> def f(x: int) -> bool
>
> I have since taken it upon myself to implement this in a fork of cpython:
> https://github.com/asleep-cult/cpython
>
> To remain consistent with function definitions, I have also added an
> alternative lambda syntax that allows you to annotate arguments and the
> return type. The syntax requires you to parenthesize the argument list:
>
> lambda (a: int, b: int) -> int: ...
>
> This new lambda syntax also allows you to create a function prototype by
> omitting the body. The original example can be rewritten as follows:
>
> def flat_map(
> l: list[int],
> func: lambda (a: int) -> int
> ) -> list[int]:
> ...
>
> Problems:
> - It is not possible to use ParamSpec with this
> - The lambda prototype syntax might be jarring
> - Some people might accidentally forget the function body
>
> Here is some feedback that I have already collected:
>
> "Yeah, making the body optional (without looking at decorators) is not
> acceptable either. Too easy to do by mistake (I still do this All. The.
> Time. :-)" - Guido van Rossum
>
> "i would strongly prefer this over the existing pep" - Ronny Pfannschmidt
>
> "I find this unnecessary and unreadable.
>
> Python isn't C or Java." - BundleOfJoysticks (Reddit)
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>
--
Christopher Barker, PhD (Chris)
Python Language Consulting
- Teaching
- Scientific Software Development
- Desktop GUI and Web Development
- wxPython, numpy, scipy, Cython
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