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Re: Why "symbol's value" error about a list?

From: Eli Zaretskii
Subject: Re: Why "symbol's value" error about a list?
Date: Tue, 06 Feb 2018 06:13:13 +0200

> Date: Mon, 5 Feb 2018 13:46:38 -0800 (PST)
> From: Drew Adams <address@hidden>
> Cc: Eli Zaretskii <address@hidden>, address@hidden,
>         address@hidden
> > The error message given out is:
> >     Symbol's value as variable is void: ’bar
> That was the old, and legitimate, error message, yes.  It
> accurately describes what is really going on (as you describe
> well, below).
> Now the message is instead (invalid-read-syntax "strange quote"
> "’").  Is that better?

I think it's somewhat better, because it talks about "strange quote",
which is a hint for the user about the actual problem.

> I suggested that the variable name be enclosed in `...'.  That
> would make the original message clearer, I think:
>   Symbol's value as variable is void: `’bar'

That might make things even more confusing, because the text actually
displayed will be this:

    Symbol’s value as variable is void: ‘’bar’

which loses all hints of what is being quoted here.

> > This is a result of the change in `message', silently to convert ' to a
> > curly quote, by default.  Some of us were unhappy at this change and
> > protested against it.
> Count me as one of those "some of us".  Echoing Lisp code
> should do just that - no fiddling to "prettify" apostrophe to
> curly quote etc.

That ship has sailed two Emacs releases ago.  We are trying to fix the

And strange quotes is only one situation where confusingly similar
characters can be presented in error messages, making it hard for
users to spot the real problem.  We are trying to find ways of making
such "typos" more evident in error messages.

> The error is using a symbol as a variable, when it is not
> defined as a variable.  Which is exactly what the original
> error message said.
> That's the LISP error.  Is there a _user error_ here?
> Yes, it's the mistake of copying and pasting what was
> printed in *Messages*.
> That user mistake is excusable.  And we would want to
> inform the user about it, if we can't prevent it.  But
> changing Lisp read syntax to guess what might be the
> most helpful thing to tell a user here is NOT the solution.

The issue is what _would_ be a helpful message in these cases.  You
are just saying what should _not_ be done (repeatedly), but that
doesn't advance us towards the solution.

> Should this Lisp syntax change be reverted?  That's the
> question being discussed here.

No, that's only part of the question.  The other, no less important
part is if we revert that change, how to make the confusing error
message less so and more helpful in understanding the user error.

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