[Python-ideas] pep 312 - implicit lambdas idea

[ilya]

I'd like to use this syntax only in situations of PEP 312, that is,
where a colon is prohibited by current grammar. In those situations,
writing _: is also prohibited by current grammar so it will be parsed
unambiguously.

The examples you quoted will not change under my idea, but ``x =
(_:_*2)`` would be possible as an alternative. Note that I would be
against being able to use ``x = _:_*2``. I think it's better to
require either lambda keyword or parentheses for the RHS of the
assignment as colon has a well-defined meaning as starting an indented
block unless it's inside some brackets.

On Fri, Aug 7, 2009 at 4:58 PM, Gerald Britton<gerald.britton at gmail.com> wrote:
> The underscore is already a viable identifier:
>>>> _ = lambda x:x*2
>>>> _(3)
> 6
> and
>>>> x = lambda _:_*2
>>>> x(3)
> 6
>>>>
>
> So I don't think you can use it the way you're proposing without breaking
> existing programs
>
> On Fri, Aug 7, 2009 at 8:46 AM, ilya <ilya.nikokoshev at gmail.com> wrote:
>>
>> I was thinking about a good syntax for implicit lambdas for a while
>> and today I had this idea: make ``_:`` a shortcut for ``lambda
>> _=None:``
>>
>> For example:
>>
>>    map( _: _ + 5, some_list)
>>    register_callback( _: True)
>>    def apply_transform(..., transform = _:_, ... ):
>>
>> but still
>>
>>    addition = lamba x, y: x + y
>>
>> The rationale is that you only want to get rid of lambda keyword to
>> create a *very* simple function, the one that will be called either
>> without parameters or with only one parameter. For everything more
>> complicated, you really should go and write the explicit function
>> signature using lambda.
>>
>> Even though ``:`` could theoretically denote implicit lambda, it's too
>> easy to miss it. The combination ``_:`` is much easier to notice. It
>> also makes explicit that there is at most one parameter and it's name
>> is ``_``. Since it's very short, it can easily be used in a long
>> function call or as a default parameter, as above
>>
>> Your thoughts?
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>
>
>
> --
> Gerald Britton
>