From: Stefan Monnier <monnier@IRO.UMontreal.CA>
To: Chong Yidong <cyd@stupidchicken.com>
Cc: emacs-devel@gnu.org
Subject: Re: e and pi
Date: Fri, 17 Sep 2010 17:11:40 +0200 [thread overview]
Message-ID: <jwvsk18fmeu.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <8739t9xpt2.fsf@stupidchicken.com> (Chong Yidong's message of "Thu, 16 Sep 2010 18:54:17 -0400")
>> Can anyone think of a better solution?
> I don't like the idea of `float-e' and `float-pi'.
> What is the problem with dynamically scoping `e' and `pi'? If it's only
> the compiler warning, we can give the compiler a whitelist of variables
> not to complain about.
It's not a question of compiler warning. It's a question of semantics.
Let's take a classic example where lexical-scoping matters: currying.
E.g. the following function
(defun make-inc (n)
(lambda (m) (+ n m)))
means that (make-inc 3) returns a function which adds 3 to its argument:
(let ((f (make-inc 3)))
(funcall f 5))
should evaluate to 8.
Now, this only works because "n" is statically scoped. So in the
current lexbind branch (where e is defined as a global/dynamic
variable), the below code would not do the same:
(defun make-inc (e)
(lambda (f) (+ e f)))
because "e" happens to be a predefined global variable with
dynamic-scoping semantics. Now for people who use such magic numerical
constants often (e.g. in the context of Calc), this may seem like an
obvious no-no, but for a poor theoretician like me who uses "e"
days-in-days-out to mean "expression", not being able to reliably use
"e" as a free variable of a closure is a real trap.
BTW, the worst of the two is `e' and AFAIK it only has a single use in
Emacs, which is as the initial value of the register "e" in
calculator.el.
At least `pi' is used a few more times, and it is not let-bound
anywhere, so we could decide to make `pi' lexically-scoped and it would
apparently work OK, but `e' OTOH is let-bound at many places, so it's
not at all obvious that making it lexically-scoped wouldn't introduce
subtle bugs. Of course, this idea of making `pi' and `e' lexically
scoped itself depends on how one would force lexical-scoping for a few
special vars in files compiled with dynamic-scoping; something which the
current lexbind doesn't support right now.
Stefan
PS: Oddly enough, SML has a similar trap where "o" is predefined as the
function-composition operator and "op" is a rarely used reserved
keyword, and I think everyone agrees by now that these were
bad decisions.
next prev parent reply other threads:[~2010-09-17 15:11 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-16 13:25 e and pi Stefan Monnier
2010-09-16 13:44 ` Deniz Dogan
2010-09-16 15:37 ` Stefan Monnier
2010-09-16 13:47 ` Leo
2010-09-16 15:39 ` Stefan Monnier
2010-09-16 14:27 ` Helmut Eller
2010-09-16 15:44 ` Stefan Monnier
2010-09-16 18:52 ` Helmut Eller
2010-09-16 14:44 ` Jason Rumney
2010-09-16 22:54 ` Chong Yidong
2010-09-17 0:04 ` Deniz Dogan
2010-09-17 0:14 ` Wojciech Meyer
2010-09-17 7:00 ` David Kastrup
2010-09-17 8:09 ` Simon Leinen
2010-09-17 8:15 ` David Kastrup
2010-09-17 9:06 ` Stephen J. Turnbull
2010-09-17 9:21 ` David Kastrup
2010-09-17 9:47 ` Helmut Eller
2010-09-17 15:11 ` Stefan Monnier [this message]
2010-09-17 15:22 ` Lars Magne Ingebrigtsen
2010-09-17 15:56 ` Helmut Eller
2010-09-17 22:13 ` Stefan Monnier
2010-09-17 15:44 ` Wojciech Meyer
2010-09-17 15:50 ` Chong Yidong
2010-09-17 16:06 ` Wojciech Meyer
2010-09-17 16:18 ` Helmut Eller
2010-09-17 16:45 ` Glenn Morris
2010-09-17 17:14 ` Glenn Morris
2010-09-18 10:01 ` Eli Zaretskii
2010-09-18 10:21 ` Helmut Eller
2010-09-18 11:07 ` Eli Zaretskii
2010-09-18 11:26 ` Helmut Eller
2010-09-18 10:50 ` David Kastrup
2010-09-18 11:09 ` Eli Zaretskii
2010-09-18 14:27 ` Stephen J. Turnbull
2010-09-18 14:32 ` Andreas Schwab
2010-09-18 15:11 ` Drew Adams
2010-09-17 22:17 ` Stefan Monnier
2010-09-18 1:10 ` Chong Yidong
2010-09-18 8:30 ` Stefan Monnier
2010-09-18 19:10 ` Chong Yidong
2010-09-18 21:37 ` Uday S Reddy
2010-09-19 0:57 ` Drew Adams
2010-09-18 13:43 ` Juanma Barranquero
2010-09-18 14:53 ` Stefan Monnier
2010-09-18 15:01 ` Lars Magne Ingebrigtsen
2010-09-18 16:00 ` Stefan Monnier
2010-09-19 10:07 ` Juanma Barranquero
2010-09-17 16:14 ` Drew Adams
2010-09-18 15:12 ` tomas
2010-09-18 17:52 ` David Kastrup
2010-09-19 19:13 ` tomas
2010-09-17 23:35 ` Uday S Reddy
2010-09-17 16:55 ` Sam Steingold
2010-09-17 22:16 ` Stefan Monnier
2010-09-17 22:55 ` Drew Adams
-- strict thread matches above, loose matches on Subject: below --
2010-09-17 4:20 MON KEY
2010-09-18 5:58 MON KEY
2010-09-18 14:50 ` Stefan Monnier
2010-09-19 2:03 ` MON KEY
2010-09-18 16:07 ` David De La Harpe Golden
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