Syntax for one-line "nonymous" functions in "declaration style"

[Alexey Muranov]

On mer., Mar 27, 2019 at 5:00 PM, python-list-request at python.org wrote:
> On 27/03/19 09:21, Alexey Muranov wrote:
>>  Whey you need a simple function in Python, there is a choice 
>> between a
>>  normal function declaration and an assignment of a anonymous 
>> function
>>  (defined by a lambda-expression) to a variable:
>> 
>>     def f(x): return x*x
>> 
>>  or
>> 
>>     f = lambda x: x*x
>> 
>>  It would be however more convenient to be able to write instead just
>> 
>>     f(x) = x*x
>> 
>>  (like in Haskell and such).
>> 
>>  Have this idea been discussed before?
>> 
>>  I do not see any conflicts with the existing syntax.   The following
>>  would also work:
> 
> I don't know. Something like the following is already legal:
> 
> f(x)[n] = x * n
> 
> And it does something completly different.
> 

Thanks for pointing out this example, but so far i do not see any issue 
with this.

Of course assignment (to an identifier) is a completely different type 
of operation than in-place mutation (of an object) with __setitem__, 
etc.

In

    <...> [<...>] = <...>

the part to the left of "[<...>]=" is an expression that is to be 
evaluated, and only its value matters.  Here "[]=" can be viewed as a 
method call, which is distinguished by the context from "[]" method 
call (__getitem__).

In

    <identifier> = <...>

the <identifier> is not evaluated.

I still think that

    <identifier>(<identifiers>)...(<identifiers>) = <...>

is unambiguous.  The following seems possible too:

    a[m][n](x)(y) = m*x + n*y

It would be the same as

    a[m][n] = lambda x: lambda y: m*x + n*y

Here a[m] is evaluated, and on the result the method "[]=" 
(__setitem__) is called.

Basically, "()...()=" seems to technically fit all contexts where "=" 
fits...

Alexey.