Re: How the backquote and the comma really work?

[Michael Heerdegen <michael_heerdegen@web.de>]

Marcin Borkowski <mbork@mbork.pl> writes:

> So, I assume that when Emacs Lisp interpreter encounters a backquote

It's even less mystical: backquote is just a normal macro:

  C-h f ` RET

It's also a reader macro so that you can write

  `thing

as an abbreviation of of

 (` thing)

but that's just a detail.

> If it is a list, its element are read and scanned.  If any part of the
> list (probably a nested one) begins with a comma, the whole thing after
> the comma (be it a symbol, a list or whatever) is evaluated as usual,
> and the result is put into the resulting list.
>
> Whew.  Is that (more or less) right?

Seems to be a reasonable mental model.  Of course, the elements have
already been read by the reader.  Whether these are evaluated or not
depends on whether the macro finds the `backquote-unquote-symbol' in
front of them, so to say.

> so a bonus question is: can I find an Emacs Lisp metacircular
> evaluator (taking into account the quoting mechanisms) anywhere?

You don't need a meta thing, since backquote is completely implemented
in Elisp, just read the source code ;-)


Regards,

Michael.