Re: Elisp programming style

[Thorsten <quintfall@googlemail.com>]

Eric Schulte <schulte.eric@gmail.com> writes:

Hi Eric, 

> Hmmm, this looks suspiciously like the case in some Babel functions :)

well ... ;)

> in which we originally has instances of the first style and then had to
> manually transition to the second.  IMO the first is very poor form, the
> variables are technically "free variables" when defined in the helper,
> and just through undocumented variable capture does the execution work
> out correctly, this can lead to unpleasant bugs.
>
> The means the helper may only be used when variables of certain names
> are in scope.
>
> If you do want to use a helper which uses variables in scope which
> aren't passed as arguments (again just my opinion) you should defined
> the helper function using `flet' *inside* of the main function and the
> scope of the variables.

That sounds like an operational prescription to me, and I think will
follow this advice in the future.

>> Would that be considered bad style from the original author, or is that
>> up to personal choice and not considered a problem?
>>
>
> I don't believe we have an official canon of such rules, but personally
> I would consider this to be bad style.  If the helper function is only
> used in one main function then it should be defined using flet, if it is
> used across multiple functions then the in-scope variables should be
> passed as explicit arguments (preferably with names other than those
> which it has in scope so you can be sure you are actually using the
> arguments).
>
> Finally, I believe the emacs-lisp compiler would complain about such
> free variables.
>
> Hope this helps, Best -- Eric

yes that helped, thanks

cheers
-- 
Thorsten