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Re: How the backquote and the comma really work?
From: |
Michael Heerdegen |
Subject: |
Re: How the backquote and the comma really work? |
Date: |
Sun, 12 Jul 2015 17:54:24 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux) |
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.
- Re: How the backquote and the comma really work?, Marcin Borkowski, 2015/07/10
- Re: How the backquote and the comma really work?,
Michael Heerdegen <=
- Re: How the backquote and the comma really work?, Marcin Borkowski, 2015/07/12
- Re: How the backquote and the comma really work?, Marcin Borkowski, 2015/07/12
- Re: How the backquote and the comma really work?, Marcin Borkowski, 2015/07/14
- Re: How the backquote and the comma really work?, Emanuel Berg, 2015/07/14
- Re: How the backquote and the comma really work?, Michael Heerdegen, 2015/07/21
- Re: How the backquote and the comma really work?, Michael Heerdegen, 2015/07/24
- Re: How the backquote and the comma really work?, Michael Heerdegen, 2015/07/21
- Re: How the backquote and the comma really work?, Michael Heerdegen, 2015/07/21