From: "andlind@gmail.com" <andlind@gmail.com>
To: help-gnu-emacs@gnu.org
Subject: Re: Why looking-at-p works?
Date: Tue, 15 May 2018 01:34:36 -0700 (PDT) [thread overview]
Message-ID: <048df544-2003-4bdf-91ea-8ed78a70dc8b@googlegroups.com> (raw)
In-Reply-To: <86r2oxsi4o.fsf@zoho.com>
On Tuesday, 6 March 2018 09:50:03 UTC+1, Emanuel Berg wrote:
> Do you need dynamic scope for `let' to work
> like that?
It depends on if the variable has been declared using `defvar' or not.
If is has beed declared with `defvar' then `let' will behave in the same way -- it appears as though the global variable is temporary changed in the body and in functions called from the body. In fact, this has been the standard way change a global variable in elisp for many years, and I guess no one was prepared to change it.
On the other hand, if the variable hasn't been declared then a statically scoped program will create a true local variable that doesn't affect called functions, whereas a dynamically scoped program would create a variable that would hide variables with the same name in outer scopes. (Reservation: I haven't verified this myself.)
Personally, I think elisp took a wrong turn when they retrofitted statically scopes to elisp. It would have been better to introduce a new primitive, say `slet', to create a static binding, regardless if the variable was global or not.
-- Anders
Ps. If you use the package `lisp-font-lock-extra', variables bound e.g. by `let' will be highlighted, and the package will highlight local and globally declared variables differently. This helps you to avoid accidentally overwriting generically named global variables like `features' and `mode-name'.
next prev parent reply other threads:[~2018-05-15 8:34 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.10182.1520323093.27995.help-gnu-emacs@gnu.org>
2018-03-06 8:49 ` Why looking-at-p works? Emanuel Berg
2018-05-15 8:34 ` andlind [this message]
2018-05-15 8:49 ` tomas
2018-03-06 7:57 Marcin Borkowski
2018-03-06 18:53 ` John Mastro
2018-03-06 20:42 ` Marcin Borkowski
2018-03-06 22:23 ` Drew Adams
2018-03-07 9:09 ` Marcin Borkowski
2018-03-07 13:06 ` Marcin Borkowski
2018-03-07 19:53 ` Eli Zaretskii
2018-03-08 4:20 ` Marcin Borkowski
2018-03-08 4:40 ` Eli Zaretskii
2018-03-08 20:33 ` Marcin Borkowski
2018-03-06 23:17 ` Nick Dokos
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