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authorRichard M. Stallman <rms@gnu.org>1994-04-29 10:16:53 +0000
committerRichard M. Stallman <rms@gnu.org>1994-04-29 10:16:53 +0000
commitff2806758e7722e6e1f02d2b40c85d6678443dd0 (patch)
tree1b2b26b5d50fd35a4238cdef365ce23d66bad828 /lispref/variables.texi
parent71e3a2a6c4c811edcc6edb222431a2cf51995315 (diff)
downloademacs-ff2806758e7722e6e1f02d2b40c85d6678443dd0.tar.gz
*** empty log message ***
Diffstat (limited to 'lispref/variables.texi')
-rw-r--r--lispref/variables.texi45
1 files changed, 29 insertions, 16 deletions
diff --git a/lispref/variables.texi b/lispref/variables.texi
index 2b12607d488..ffee1a39c45 100644
--- a/lispref/variables.texi
+++ b/lispref/variables.texi
@@ -20,7 +20,7 @@ symbol. The use of a symbol as a variable is independent of its use as
a function name. @xref{Symbol Components}.
The Lisp objects that constitute a Lisp program determine the textual
-form of the program--it is simply the read syntax for those Lisp
+form of the program---it is simply the read syntax for those Lisp
objects. This is why, for example, a variable in a textual Lisp program
is written using the read syntax for the symbol that represents the
variable.
@@ -166,7 +166,7 @@ binding.
local bindings.
@defspec let (bindings@dots{}) forms@dots{}
-This function binds variables according to @var{bindings} and then
+This special form binds variables according to @var{bindings} and then
evaluates all of the @var{forms} in textual order. The @code{let}-form
returns the value of the last form in @var{forms}.
@@ -217,7 +217,7 @@ form. Compare the following example with the example above for
@end example
@end defspec
- Here is a complete list of the other facilities which create local
+ Here is a complete list of the other facilities that create local
bindings:
@itemize @bullet
@@ -365,9 +365,11 @@ more precisely, if its current binding is not void. It returns
@node Defining Variables
@section Defining Global Variables
+@cindex variable definition
You may announce your intention to use a symbol as a global variable
-with a definition, using @code{defconst} or @code{defvar}.
+with a @dfn{variable definition}: a special form, either @code{defconst}
+or @code{defvar}.
In Emacs Lisp, definitions serve three purposes. First, they inform
people who read the code that certain symbols are @emph{intended} to be
@@ -381,7 +383,7 @@ variables in a program.
a matter of intent, serving to inform human readers of whether programs
will change the variable. Emacs Lisp does not restrict the ways in
which a variable can be used based on @code{defconst} or @code{defvar}
-declarations. However, it also makes a difference for initialization:
+declarations. However, it does make a difference for initialization:
@code{defconst} unconditionally initializes the variable, while
@code{defvar} initializes it only if it is void.
@@ -518,7 +520,7 @@ pi
@defun user-variable-p variable
@cindex user option
-This function returns @code{t} if @var{variable} is a user option--- a
+This function returns @code{t} if @var{variable} is a user option---a
variable intended to be set by the user for customization---and
@code{nil} otherwise. (Variables other than user options exist for the
internal purposes of Lisp programs, and users need not know about them.)
@@ -647,8 +649,7 @@ This function sets @var{symbol}'s value to @var{value}, then returns
@var{symbol} is evaluated to obtain the symbol to set.
The most-local existing binding of the variable is the binding that is
-set; shadowed bindings are not affected. If @var{symbol} is not
-actually a symbol, a @code{wrong-type-argument} error is signaled.
+set; shadowed bindings are not affected.
@example
@group
@@ -681,18 +682,26 @@ one
@end group
@end example
+If @var{symbol} is not actually a symbol, a @code{wrong-type-argument}
+error is signaled.
+
+@example
+(set '(x y) 'z)
+@error{} Wrong type argument: symbolp, (x y)
+@end example
+
Logically speaking, @code{set} is a more fundamental primitive than
@code{setq}. Any use of @code{setq} can be trivially rewritten to use
@code{set}; @code{setq} could even be defined as a macro, given the
availability of @code{set}. However, @code{set} itself is rarely used;
-beginners hardly need to know about it. It is needed for choosing which
-variable to set is made at run time. For example, the command
+beginners hardly need to know about it. It is useful only for choosing
+at run time which variable to set. For example, the command
@code{set-variable}, which reads a variable name from the user and then
sets the variable, needs to use @code{set}.
@cindex CL note---@code{set} local
@quotation
-@b{Common Lisp note:} in Common Lisp, @code{set} always changes the
+@b{Common Lisp note:} In Common Lisp, @code{set} always changes the
symbol's special value, ignoring any lexical bindings. In Emacs Lisp,
all variables and all bindings are (in effect) special, so @code{set}
always affects the most local existing binding.
@@ -726,7 +735,7 @@ located textually within the function or block that binds the variable.
@cindex CL note---special variables
@quotation
@b{Common Lisp note:} variables declared ``special'' in Common Lisp
-are dynamically scoped like variables in Emacs Lisp.
+are dynamically scoped, like variables in Emacs Lisp.
@end quotation
@menu
@@ -1012,7 +1021,7 @@ But @code{save-excursion} as shown here avoids the problem:
buffer-local binding of buffer @samp{b}.
When a file specifies local variable values, these become buffer-local
-value when you visit the file. @xref{Auto Major Mode}.
+values when you visit the file. @xref{Auto Major Mode}.
@node Creating Buffer-Local
@subsection Creating and Deleting Buffer-Local Bindings
@@ -1116,6 +1125,10 @@ buffer. However, if you set the variable again, that will once again
create a local binding for it.
@code{kill-local-variable} returns @var{variable}.
+
+This function is a command because it is sometimes useful to kill one
+buffer-local variable interactively, just as it is useful to create
+buffer-local variables interactively.
@end deffn
@defun kill-all-local-variables
@@ -1156,7 +1169,7 @@ change a variable's default value regardless of whether the current
buffer has a buffer-local binding. For example, you could use
@code{setq-default} to change the default setting of
@code{paragraph-start} for most buffers; and this would work even when
-you are in a C or Lisp mode buffer which has a buffer-local value for
+you are in a C or Lisp mode buffer that has a buffer-local value for
this variable.
@c Emacs 19 feature
@@ -1172,8 +1185,8 @@ variable. If @var{symbol} is not buffer-local, this is equivalent to
@end defun
@c Emacs 19 feature
-@defun default-boundp variable
-The function @code{default-boundp} tells you whether @var{variable}'s
+@defun default-boundp symbol
+The function @code{default-boundp} tells you whether @var{symbol}'s
default value is nonvoid. If @code{(default-boundp 'foo)} returns
@code{nil}, then @code{(default-value 'foo)} would get an error.