Are "proper" closures used in Emacs sources?

Are "proper" closures used in Emacs sources?

[Marcin Borkowski]

Hi all,

it's been quite some time since lexical binding was introduced to
Elisp.  Apart from possible optimizations and being less error-prone, it
allows for all the cool tricks with closures.  Are there any places in
Emacs core where "proper" closures are actually used?  (By "proper",
I mean closures with non-empty lexical environment, actually using said
environment.)

TIA,

-- 
Marcin Borkowski
http://mbork.pl

Re: Are "proper" closures used in Emacs sources?

[tomas]

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On Tue, Jan 12, 2021 at 02:50:24PM +0100, Marcin Borkowski wrote:
> Hi all,
> 
> it's been quite some time since lexical binding was introduced to
> Elisp.  Apart from possible optimizations and being less error-prone, it
> allows for all the cool tricks with closures.  Are there any places in
> Emacs core where "proper" closures are actually used?  (By "proper",
> I mean closures with non-empty lexical environment, actually using said
> environment.)

tar-next-file-displayer of tar-mode.el seems to do (CAVEAT: I just
grepped for "closure" in the .el sources, dismissed the too-obvious
false-positives and half-scanned comments and code, so I might be
off by some amount! Double-check.)

Cheers
 - t

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Re: Are "proper" closures used in Emacs sources?

[Zhu Zihao]

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Marcin Borkowski writes:

> Hi all,
>
> it's been quite some time since lexical binding was introduced to
> Elisp.  Apart from possible optimizations and being less error-prone, it
> allows for all the cool tricks with closures.  Are there any places in
> Emacs core where "proper" closures are actually used?  (By "proper",
> I mean closures with non-empty lexical environment, actually using said
> environment.)
>
> TIA,

thunk.el & generator.el 


-- 
Retrieve my PGP public key:

  gpg --recv-keys D47A9C8B2AE3905B563D9135BE42B352A9F6821F

Zihao

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Re: Are "proper" closures used in Emacs sources?

[Stefan Monnier]

> it's been quite some time since lexical binding was introduced to
> Elisp.  Apart from possible optimizations and being less error-prone, it
> allows for all the cool tricks with closures.  Are there any places in
> Emacs core where "proper" closures are actually used?  (By "proper",
> I mean closures with non-empty lexical environment, actually using said
> environment.)

Yes.  Of course, there are lots of "proper" closures used at places
where the old code used dynamic scoping instead, such as:

    (mapcar (lambda (x) (concat x y)) foo)

I.e. using "downward funargs".  But there are also several places where
we use proper closures that survive their enclosing scope.
The completion-table functions do that a fair bit, for example, as does
`cl-generic`.  `gv-ref` is another example, along with `thunk`.
Several process filters and sentinels do that as well.

And then there are all the places where we replaced

    `(lambda ...)

with proper closures.

[ And then, there's `add-function` which relies on "proper closures" but
  it does it by manually constructing the bytecode objects rather than by
  relying on the `lexical-binding` support for lexical scope, so it's
  somewhat different (it's more like the use of `(lambda ...), just with
  byte-code objects).  ]


        Stefan

Re: Are "proper" closures used in Emacs sources?

[Andrea Corallo via Emacs development discussions.]

Marcin Borkowski <mbork@mbork.pl> writes:

> Hi all,
>
> it's been quite some time since lexical binding was introduced to
> Elisp.  Apart from possible optimizations and being less error-prone, it
> allows for all the cool tricks with closures.  Are there any places in
> Emacs core where "proper" closures are actually used?  (By "proper",
> I mean closures with non-empty lexical environment, actually using said
> environment.)

I've put a print in `byte-compile-make-closure' and did a bootstrap.

I'm counting 7289 occurrences in the Emacs code base.  Is this a correct
estimation?

  Andrea

Re: Are "proper" closures used in Emacs sources?

[Stefan Monnier]

> I've put a print in `byte-compile-make-closure' and did a bootstrap.
>
> I'm counting 7289 occurrences in the Emacs code base.  Is this a correct
> estimation?

Probably, but I suspect most of them are in the "downward funarg"
category, i.e. they'd work just as well with dynamic scope because they
don't outlive their own scope.


        Stefan