From: Michael Heerdegen <michael_heerdegen@web.de>
To: Marcin Borkowski <mbork@mbork.pl>
Cc: help-gnu-emacs@gnu.org
Subject: Re: How the backquote and the comma really work?
Date: Sun, 12 Jul 2015 17:54:24 +0200 [thread overview]
Message-ID: <87zj318j7z.fsf@web.de> (raw)
In-Reply-To: <87615sxn1a.fsf@mbork.pl> (Marcin Borkowski's message of "Fri, 10 Jul 2015 13:36:01 +0200")
Hi Marcin,
sorry for the late reply.
> So here's my humble attempt at the reader itself. It does nothing
> with ticks, backticks and commas -- AFAIUC, it shouldn't be done at
> this level anyway -- it just translates them to special forms (quote
> ...), (quasi-quote ...) and (unquote ...).
Yes, that's the right approach. You could of course translate into the
symbols named "'", "`" and "," instead, like the Lisp reader does, but
that's a detail. In Elisp, these aren't special forms. They could be
in your interpreter, of course.
> Do I get it correctly that it's the eval function which should handle
> these?
In Elisp, it's not directly handled by eval, since handling the
backquote mechanism is not hardcoded. Instead, backquote is
a macro written in Lisp.
Dunno if your interpreter will support macros. If not, you could handle
backquote directly in your interpreter.
> (require 'anaphora) ; we'll use acase
It would be good if you could drop this dependence. This would spare
people from trying your code from installing additional stuff.
> (defun mci/next-token () ...
> (defun mci/read () ...
> (defun mci/read-list-contents () ...
That looks already very promising!
I never tried to write a Lisp reader in Elisp, but the general approach
seems to be appropriate (others might be able to give more and better
comments -- Drew, Stefan, Lars, ... - anyone?).
There is a problem though when the read expression is nested. I tried
to `mci/read' this string for example:
"(defun fac (x) (if (< 2 x) 1 (* x (fac (1- x)))))"
and got
(defun fac :open-paren x)
as result. If you Edebug your functions, you can see what goes wrong.
Please tell me if you need more hints...
I guess you already know that you have not chosen the easiest way to
understand backquote. Anyway, you learn a lot of stuff with your
approach. Looking forward the next version!
Regards,
Michael.
next prev parent reply other threads:[~2015-07-12 15:54 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-25 17:09 How the backquote and the comma really work? Marcin Borkowski
2015-06-25 17:33 ` Michael Heerdegen
2015-06-25 18:06 ` Marcin Borkowski
2015-06-25 18:22 ` Michael Heerdegen
2015-06-25 18:39 ` Marcin Borkowski
2015-06-25 18:44 ` Marcin Borkowski
2015-06-25 19:06 ` Michael Heerdegen
2015-07-10 11:36 ` Marcin Borkowski
2015-07-12 15:54 ` Michael Heerdegen [this message]
2015-07-12 19:55 ` Marcin Borkowski
2015-07-12 20:33 ` Marcin Borkowski
2015-07-14 18:17 ` Marcin Borkowski
2015-07-14 22:08 ` Emanuel Berg
2015-07-21 22:08 ` Michael Heerdegen
2015-07-24 13:01 ` Michael Heerdegen
2015-08-11 11:41 ` Marcin Borkowski
2015-08-12 15:29 ` Michael Heerdegen
[not found] ` <mailman.8207.1439393377.904.help-gnu-emacs@gnu.org>
2015-08-12 16:30 ` Pascal J. Bourguignon
2015-08-23 8:30 ` Marcin Borkowski
[not found] ` <mailman.110.1440318650.11330.help-gnu-emacs@gnu.org>
2015-08-23 16:46 ` Pascal J. Bourguignon
2015-07-21 21:54 ` Michael Heerdegen
2015-08-11 10:15 ` Marcin Borkowski
2015-08-11 17:20 ` Thorsten Jolitz
2015-08-12 15:01 ` Michael Heerdegen
2015-07-21 21:50 ` Michael Heerdegen
2015-06-25 18:10 ` Drew Adams
2015-06-25 18:40 ` Michael Heerdegen
2015-06-25 18:53 ` Marcin Borkowski
2015-06-25 19:39 ` Michael Heerdegen
2015-06-25 20:05 ` Drew Adams
2015-06-25 20:18 ` Marcin Borkowski
2015-06-25 20:37 ` Drew Adams
2015-06-25 23:55 ` Robert Thorpe
[not found] ` <mailman.5697.1435276533.904.help-gnu-emacs@gnu.org>
2015-06-26 1:41 ` Rusi
2015-06-26 14:24 ` Michael Heerdegen
[not found] ` <mailman.5716.1435328741.904.help-gnu-emacs@gnu.org>
2015-06-26 14:35 ` Rusi
2015-06-26 14:51 ` Michael Heerdegen
2015-06-25 18:46 ` Marcin Borkowski
2015-06-26 7:31 ` tomas
2015-06-26 13:48 ` Drew Adams
2015-06-26 14:06 ` tomas
2015-06-26 15:06 ` Emanuel Berg
2015-07-12 17:38 ` Vaidheeswaran C
[not found] <mailman.5657.1435252169.904.help-gnu-emacs@gnu.org>
2015-06-30 16:27 ` sokobania.01
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