On Thursday, July 14, 2016 at 12:49:58 PM UTC+9, ZyX wrote:
> 2016-07-13 19:17 GMT+03:00 mattn <mattn...@gmail.com>:
> > On Wednesday, July 13, 2016 at 4:11:59 AM UTC+9, Bram Moolenaar wrote:
> >
> > Well, I wonder this lambda will be useful. At the first, we hoped to call
> > statements in lambda. But the implementation you will include into vim
> > can't do because it only allow expressions. It's similar to python's
> > lambda. python's one doesn't allow statements. So usecase are limited to
> > use. I don't have strong opinion but I'm thinking that this is an new
> > expresssion or language for the lambda. It will demand to learn the new
> > expression for the users.
>
> Vim has `execute()`. Python-3 has `exec()` function (Python-2 has it
> as a statement). Lambdas do not usually allow statements because they
> are to be used in contexts which requires return value (e.g. in Python
> this is sorted()/list.sort(), defaultdict(), re.sub[n] (BTW, it is
> good idea to have `substitute(s, pattern, funcref, flags)` to work
> like `substitute(s, pattern, '\=funcref(submatch(0), submatch(1), …)',
> flags)`)). Lambdas are also used as a replacement for
> `functools.partial` (python)/`function(fref, args, self)` (VimL) in
> cases when they do not apply (e.g. when one needs to fix not the
> first, but second or other arguments), but this requires closures.
execute() doesn't have scope. So:
call execute("let a = 1")
echo 1
This define new variable in global scope. I want anonymous function. If
execute() works with the scope, for example "let a = 1" mean "let l:a = 1",
It's so great.
> If you need lambda with statement then most likely you are going to
> create unreadable code. Good lambdas are *small*, all examples you
> have shown in documentation are either
>
> 1. More readable with new lambda style. It is absolutely not needed to
> write `return` and `a:` in `sort()` or `map()` callbacks.
> 2. Not practical. I still want to see an example of timer callback
> which is used for more practical applications then testing timers
> (like your echo) and yet is more readable with your variant of lambda
> among variants a) :function, b) new lambda style (+ execute()!) and c)
> your lambda style.
The arrow operator which bram suggested is new, I think.
> 3. Needs closures and not lambdas. I would not really say that your
> example with multiline lambda used for counter generator is better
> then with :function. Though it actually needs no closures in the
> current state:
>
> function s:counter(x)
> let d = {'x': a:x}
> function d.counter()
> let self.x += 1
> return self.x
> endfunction
> return d.counter
> endfunction
>
> And there is no new language, expressions are already used in a number
> of places.
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