Re: curious why private variables are rare

[Emanuel Berg <incal@dataswamp.org>]

Samuel Wales wrote:

> the usual thing is:
>
>   (defvar var ...)
>   (defun fun ...)

I hope not, as that introduces a global/dynamic/special
variable ...

> even when var is only used by fun.  but you could do:
>
>   (let ((var ...))
>     (defun fun ...))

Yes, a lexical let-closure.

Here [1] is an example of the two use cases I've found so far

  https://dataswamp.org/~incal/emacs-init/w3m/w3m-survivor.el

The use-cases are

  (1) state variables that don't change between function calls
  
  (2) share variables between functions

(The `declare-function' stuff is to shut up the byte-compiler.)

> [at least, i /think/ you can do this with similar results from the
> perspective of the function

You think right!

> the most obvious drawback of the latter would probably be
> convenience in debugging/inspectability/discoverability.
> re-using a variable name could be confusing. other than that
> and extra indentation, i'm not sure if there are
> big drawbacks.

I don't think there are any drawbacks to closures, it's a good
way, maybe the best way, to do (1) and (2).

> it would limit scope so you don't pollute completion,
> apropos, etc. you can eliminate prefix. no stomp on vars.

If so, that's a problem for completion etc.

[1] https://dataswamp.org/~incal/emacs-init/w3m/w3m-survivor.el

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