On Sun, Oct 24, 2021 at 1:48 PM Bruce Leban <bruce@leban.us> wrote:
>
>
> On Sat, Oct 23, 2021 at 6:23 PM Jelle Zijlstra <jelle.zijlstra@gmail.com> wrote:
>>
>> In the PEP's example:
>>
>> def bisect_right(a, x, lo=0, hi=>len(a), *, key=None):
>>
>> This reads to me like we're putting "hi" into "len(a)", when it's in fact the reverse.
>
> Every language I am aware of that has adopted a short hand lambda notation (without a keyword) has used => or -> except APL, Ruby, SmallTalk. See https://en.wikipedia.org/wiki/Anonymous_function
Anonymous functions are an awkward parallel here. The notation you're
describing will create a function which accepts one argument, and then
returns a value calculated from that argument. We're actually doing
the opposite: hi is being set to len(a), it's not that len(a) is being
calculated from hi.
That said, though, I still count "=>" among my top three preferences
(along with "=:" and "?="), and flipping the arrow to "<=" is too
confusable with the less-eq operator.
Sorry I was less than clear. The syllogism here is
(1) late-evaluated argument default should use => because that's the proposal for shorthand lambda
(2) shorthand lambda should use => because that's what other languages use.
I was talking about (2) but I should have been explicit. And yes, you highlight a potential source of confusion.
def f(x=>x + 1): ...
means that x is 1 more than the value of x from the enclosing global scope (at function call time) while
g = x => x + 1
sets g to a single-argument function that adds 1 to its argument value.
--- Bruce