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Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...)))
From: |
Thien-Thi Nguyen |
Subject: |
Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))) |
Date: |
Tue, 04 Jan 2011 19:12:21 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) |
() Richard Stallman <address@hidden>
() Mon, 03 Jan 2011 11:15:11 -0500
It is un-lispy for a special symbol in the middle of
a list to change the way that list is used.
Hmm. I guess that this is the same grounds for your
unease with keyword arguments. Close? My take on the
lispiness of this change is:
- We are already dealing with a construct where the
treatment of the list is non-uniform (EXPR vs BODY),
so playing in the "neck" area has precedence: special
handling of docstring, ‘interactive’ form, indentation
hints (for ‘defmacro’), etc.
- Functional style is not unlispy. It's true that a
large body of Emacs Lisp is written with assignments
(and will continue to be done that way), but that is
hardly elegant. It would be nice to bolster this
argument with "and hardly needed", supplying stats
gathered from lisp/* on how often a local variable is
declared only to be used in communication between a
cond's EXPR and BODY forms, but i haven't done that,
yet. (Anyone want to beat me to it?)
Having said that, i readily admit my relative inexperience
with Lisp (Emacs Lisp or otherwise). It could be that what i
hold dear as lispy is actually more schemey than anything...
Now for some thoughts on:
Here's another syntax that makes it all much simpler.
(cond VAR COND-CLAUSES...)
[...]
The same variable gets used for each clause, but if
you want to change to a different one, just write
another top-level symbol:
(cond
tail
((cdr list) (car tail))
first
((car list) (car first)))
Really, what i want to do is elide variable names entirely,
for what i regard as essentially an internal (to each clause)
affair. Any communication outside of that scope is a lose
(or rather, is the status quo, which is less than winning).
Only the last cond variable gets set, and not if it's nil.
So you can also write this:
(cond temp first nil
((setq temp (cdr list)) (car temp))
((setq first (car list)) (car first)))
That is more explicit. It is not quite as brief,
but it s still better than this:
(cond
((cdr list) -> (lambda (temp) (car temp)))
((car list) -> (lambda (first) (car first))))
Currently you can write this,
(let (temp first)
(cond
((setq temp (cdr list)) (car temp))
((setq first (car list)) (car first))))
so the alternatives proposed above are not a tremendous
improvement, just a small improvement. But even the small
improvement might be good, since it improves readability.
I should clarify. The original proposal should read:
(cond (EXPR => 1-ARY-FUNC) ...)
In other words, the (lambda (VAR) ...) does the job,
but is not required. So, the example expression you
gave above can actually be made even more succinct:
(cond
((cdr list) => #'car)
((car list) => #'car)
No variables at all!
- emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Thien-Thi Nguyen, 2011/01/02
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Stefan Monnier, 2011/01/02
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Richard Stallman, 2011/01/03
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))),
Thien-Thi Nguyen <=
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Stefan Monnier, 2011/01/05
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Harald Hanche-Olsen, 2011/01/05
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Stefan Monnier, 2011/01/05
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Helmut Eller, 2011/01/06
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Stefan Monnier, 2011/01/06
- Re: emacs lisp syntax rfc: (cond (EXPR => (lambda (X) ...))), Richard Stallman, 2011/01/06