Re: for a given emacs session: insert a subject with an increasing counter

[Eric Abrahamsen <eric@ericabrahamsen.net>]

Emanuel Berg <moasenwood@zoho.eu> writes:

>>> That's called a "closure", because the function "closes
>>> over" the let-bound symbol. Once evaluated, _only_ the
>>> function body has access to that symbol: it can treat it
>>> like a globally-defined variable, but no one else can see
>>> it. When lexical-binding is non-nil, you're always making
>>> closures:
>>>
>>> (setq lexical-binding t)
>>> (lambda (arg) (message "%S" arg)) -->
>>>   (closure (t) (arg) (message "%S" arg))
>>>
>>> The (t) is where the closed-over symbols and their current
>>> values would be stored, if there were any. It's sort of
>>> like the function's own private let-form.
>>
>> But ... isn't that what you get with lexical/static `let'
>> _in_ the function?
>
> Ah, now I understand what you mean. With `let' inside, the
> variable will reset, so it cannot count, but with `let'
> outside (the closure), as you say "it can treat it like
> a globally-defined variable".

That's right.

> "globally-defined", very good!
>
> Oh, no!
>
> I didn't know of this (never seen it). I have used global
> variables to hold the "state" (be a memory between function
> calls) but I've also done more involved solutions like
> properties and even self-modifying code :O
>
> And all the while, it was this easy ...

TBH, I've never actually used a closure in anger, probably just because
it doesn't occur to me. I'll bet if I went back and looked over the code
I've written in the past I could find some situations where I could have
used them, but... *shrug*