From: Michael Heerdegen <michael_heerdegen@web.de>
To: help-gnu-emacs@gnu.org
Subject: Re: How the backquote and the comma really work?
Date: Wed, 12 Aug 2015 17:29:18 +0200 [thread overview]
Message-ID: <87h9o4ed9t.fsf@web.de> (raw)
In-Reply-To: 87h9o6gihr.fsf@mbork.pl
Marcin Borkowski <mbork@mbork.pl> writes:
> Interestingly, there's a lot of buzz about Lisp /interpreter/ written
> in Lisp, but not so much about Lisp /reader/ written in Lisp. In
> fact, I didn't find one on the Internet.
Good question. Maybe it's because doing such things is mainly for
educational reasons, and when you want to learn how a language works,
studying the interpreter is more beneficial.
> What I found was Peter Norvig's tiny Lisp written in Python
> (http://norvig.com/lispy.html). His reader is quite simple, but there
> is an important difference: he reads all the tokens into a (Python)
> list, and then he can "peek" at the next token without "consuming" it.
> In my approach, this is not possible (well, it is of course possible,
> but moving the point back so that the same token will be read again is
> ugly).
What disadvantages do you fear could your version have?
On the page you cited, the flat list is only used as an intermediate
step to produce the syntax tree. There is not much more you could do
with it.
And if you want to re-read any form in some buffer, putting point back
to its beginning is a fast operation.
> Now I'm wondering: is my approach (read one token at a time, but never
> go back, so that I can't really "peek" at the next one) reasonable?
> Maybe I should just read all tokens in a list? I do not like this
> approach very much. I could also set up a buffer, which would contain
> zero or one tokens to read, and put the already read token in that
> buffer in some cases (pretty much what TeX's \futurelet does. Now
> I appreciate why it's there...).
I really don't get the point in which way the Python example would have
advantages over yours. The only difference is that your version
combines the two steps that are separate in the Python example. Your
version is more efficient, since it avoids building a very long list
that is not really needed and will cause a lot of garbage collection to
be done afterwards.
Regards,
Michael.
next prev parent reply other threads:[~2015-08-12 15:29 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
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 [this message]
[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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87h9o4ed9t.fsf@web.de \
--to=michael_heerdegen@web.de \
--cc=help-gnu-emacs@gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this external index
https://git.savannah.gnu.org/cgit/emacs.git
https://git.savannah.gnu.org/cgit/emacs/org-mode.git
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.