[Python-ideas] A simple proposal concerning lambda

[MRAB]

On 2018-08-22 02:38, Elazar wrote:
> I don't think this change makes sense, but if it's done, there should be 
> another change, with actual implications:
> There is no way to express the types of the parameters in a lambda - 
> `lambda x: int : x` is obviously a syntax error. Replacing the colon 
> with a different symbol, such as "=>" will make this possible:
> 
>      def x => x
>      def x: int => x
>      def x: int -> int => x
> 
> It will also give one less meaning to the colon.
> 
The examples I showed had parens, so your examples could be:

     def (x): x
     def (x: int): x
     def (x: int) -> int: x

> 
> On Tue, Aug 21, 2018 at 6:28 PM MRAB <python at mrabarnett.plus.com 
> <mailto:python at mrabarnett.plus.com>> wrote:
> 
>     On 2018-08-22 01:25, Jonathan Fine wrote:
>      > Hi Abe
>      >
>      > Summary: You've done good work here. I've skim read the 2006
>      > discussion you found.
>      >
>      > You wrote:
>      >
>      >> I'm trying to dig up past threads about alternatives to lambda
>     because I
>      >> would be astonished if "def" hadn't been considered and rejected
>     for some
>      >> reason. What I've found so far is this unreassuring  post from
>     Guido back in
>      >> 2006
>      >
>      >> [Python-Dev] Let's just *keep* lambda
>      >>
>     https://mail.python.org/pipermail/python-dev/2006-February/060415.html
>      >
>      > This is an excellent piece of work. I'm most grateful. Here's
>     what Guido said:
>      >
>      >> After so many attempts to come up with an alternative for lambda,
>      >> perhaps we should admit defeat. I've not had the time to follow the
>      >> most recent rounds, but I propose that we keep lambda, so as to stop
>      >> wasting everybody's talent and time on an impossible quest.
>      >
>      > I've quickly read through the posts that followed Guido's message,
>      > picked out the ones that interest me. Here's a list.
>      >
>      >>
>     https://mail.python.org/pipermail/python-dev/2006-February/060487.html
>      >>
>     https://mail.python.org/pipermail/python-dev/2006-February/060474.html
>      >>
>     https://mail.python.org/pipermail/python-dev/2006-February/060471.html
>      >>
>     https://mail.python.org/pipermail/python-dev/2006-February/060445.html
>      >>
>     https://mail.python.org/pipermail/python-dev/2006-February/060435.html
>      >>
>     https://mail.python.org/pipermail/python-dev/2006-February/060431.html
>      >>
>     https://mail.python.org/pipermail/python-dev/2006-February/060470.html
>      >
>      > And one of the messages had a link to still live and excellent page
>      >
>      >> https://wiki.python.org/moin/AlternateLambdaSyntax
>      >
>      > This page lists over 100 suggestions, mostly variants. So far as
>     I can
>      > see, my simple proposal isn't listed on that page. The page also says
>      >
>     Hmm.
> 
>     That lists:
> 
>           def (a, b, c): return f(a) + o(b) - o(c)
> 
>     and:
> 
>           def (a, b, c) = f(a) + o(b) - o(c)
> 
>     but not:
> 
>           def (a, b, c): f(a) + o(b) - o(c)
> 
>      >> **Definitely Desirable Features**
>      > [snip]
>      >> *More friendly to inexperienced users*
>      > [snip]
>      >> Compared to other Python keywords, 'lambda' is rather esoteric.
>      >> In the challenge for "farthest outside day-to-day English usage",
>      >> its closest competitor would probably be 'assert', as even 'def'
>      >> and 'elif' are just abbreviations for 'define' and 'else if'. Use of
>      >> simpler keywords may make deferred expressions appear less
>      >> intimidating than they seem with the current unusual keyword.
>      >
>      > The word 'deferred' appears 7 times on the page. It also appears in
>      > the python-dev messages.
>      >
>      > If someone with more time and less bias then myself were to summarise
>      > this discussion from 2006, I'd be most grateful, and they'd have
>      > material for a great blog post.
>      >
>      > Finally, many thanks to Abe for finding this gem, and countless
>      > people's hard work in keeping it alive to be found. Backwards
>      > compatibility is there for a reason.
>      >