procyberian/emacs
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

; Improve description of scoping and let-bindings

Browse source 
* doc/lispref/variables.texi (Local Variables, Variable Scoping):
Explain the move to lexical-binding and elaborate on 'let*'.
Suggested by Michael Heerdegen <michael_heerdegen@web.de>.
(Bug#60027)
This commit is contained in:
Eli Zaretskii 2022-12-14 17:46:16 +02:00
parent 752f9dde63
commit d51b66ed54
1 changed files with 23 additions and 4 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

27
doc/lispref/variables.texi
View file

@ -188,15 +188,18 @@ It determines the value returned by evaluating the variable symbol,
and it is the binding acted on by @code{setq}. and it is the binding acted on by @code{setq}.
For most purposes, you can think of the current binding as the For most purposes, you can think of the current binding as the
innermost local binding, or the global binding if there is no innermost local binding, or the global binding if there is no local
local binding. To be more precise, a rule called the @dfn{scoping binding. To be more precise, a rule called the @dfn{scoping rule}
rule} determines where in a program a local binding takes effect. The determines where in a program a local binding takes effect. The
default scoping rule in Emacs Lisp is called @dfn{dynamic scoping}, default scoping rule in Emacs Lisp is called @dfn{dynamic scoping},
which simply states that the current binding at any given point in the which simply states that the current binding at any given point in the
execution of a program is the most recently-created binding for that execution of a program is the most recently-created binding for that
variable that still exists. For details about dynamic scoping, and an variable that still exists. For details about dynamic scoping, and an
alternative scoping rule called @dfn{lexical scoping}, @pxref{Variable alternative scoping rule called @dfn{lexical scoping}, @pxref{Variable
Scoping}. Scoping}. Lately Emacs is moving towards using lexical binding in
more and more places, with the goal of eventually making lexical
binding the default. In particular, all Emacs Lisp source files and
the @file{*scratch*} buffer use lexical scoping.
The special forms @code{let} and @code{let*} exist to create local The special forms @code{let} and @code{let*} exist to create local
bindings: bindings:
@ -266,6 +269,17 @@ Compare the following example with the example above for @code{let}.
@result{} (1 1) @result{} (1 1)
@end group @end group
@end example @end example
@noindent
Basically, the @code{let*} binding of @code{x} and @code{y} in the
previous example is equivalent to using nested @code{let} bindings:
@example
(let ((y 1))
(let ((z y))
(list y z)))
@end example
@end defspec @end defspec
@defspec letrec (bindings@dots{}) forms@dots{} @defspec letrec (bindings@dots{}) forms@dots{}
@ -974,6 +988,11 @@ binding can also be accessed from the Lisp debugger.}. It also has
binding can live on even after the binding construct has finished binding can live on even after the binding construct has finished
executing, by means of special objects called @dfn{closures}. executing, by means of special objects called @dfn{closures}.
The dynamic binding was (and still is) the default in Emacs for many
years, but lately Emacs is moving towards using lexical binding in
more and more places, with the goal of eventually making that the
default.
The following subsections describe dynamic binding and lexical The following subsections describe dynamic binding and lexical
binding in greater detail, and how to enable lexical binding in Emacs binding in greater detail, and how to enable lexical binding in Emacs
Lisp programs. Lisp programs.