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Re: dolist considered harmful

From: Eli Zaretskii
Subject: Re: dolist considered harmful
Date: Tue, 30 Oct 2018 21:31:18 +0200

> From: Stefan Monnier <address@hidden>
> Date: Tue, 30 Oct 2018 14:39:46 -0400
> - The docstring is incomprehensible:
>       Loop over a list.
>       Evaluate BODY with VAR bound to each car from LIST, in turn.
>       Then evaluate RESULT to get return value, default nil.
>   I don't know how to loop over a list.

I think the rest of the doc string explains how.

>   "evaluate" is unclear (is it passed to   `eval`?  Then why not say it?

What "evaluation" is, is described in the section "Evaluation" of the
ELisp manual.

>   Also, in which order?

It says "each car from LIST, in turn".  I think this answers your

>   How does RESULT communicate the return value?
>   Is it RESULT which defaults to nil or the return value?
>   If the return value, then when does it default to nil?

I think this is clear from the text, I'm unsure what confused you.

> - The docstring says nothing of what happens when LIST is not a list,
>   yet a quick grep shows that most uses of dolist use for LIST a simple
>   variable rather than a list.  What gives?

There's no contradiction here.

> Since it can only be used when we're 100% sure that LIST is a LIST,
> (and who can be sure of such a thing in a dynamic language like Emacs
> Lisp), I think we'd be better off deprecating it and changing all uses
> of dolist with a clear while+cdr loop that everyone can understand.

Patches welcome.

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