Re: Native line numbers landed on master

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Mon, 07 Oct 2019 19:30:34 +0300, Eli Zaretskii <eliz@gnu.org> said:

    Eli> We have a node about writing Emacs Lisp primitives; a node about Lisp
    Eli> variables implemented in C still awaits its author.  Patches are
    Eli> welcome.

I donʼt know about a separate node. How about this:

diff --git a/doc/lispref/internals.texi b/doc/lispref/internals.texi
index c52999e1cd..54f1e8858d 100644
--- a/doc/lispref/internals.texi
+++ b/doc/lispref/internals.texi
@@ -945,7 +945,7 @@ Writing Emacs Primitives
 @anchor{Defining Lisp variables in C}
 @vindex byte-boolean-vars
 @cindex defining Lisp variables in C
-@cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL}
+@cindex @code{DEFVAR_INT}, @code{DEFVAR_LISP}, @code{DEFVAR_BOOL}, @code{DEFSYM}
   The function @code{syms_of_@var{filename}} is also the place to define
 any C variables that are to be visible as Lisp variables.
 @code{DEFVAR_LISP} makes a C variable of type @code{Lisp_Object} visible
@@ -956,6 +956,38 @@ Writing Emacs Primitives
 defined with @code{DEFVAR_BOOL} are automatically added to the list
 @code{byte-boolean-vars} used by the byte compiler.
 
+  These macros all expect three arguments:
+
+@table @code
+@item lname
+The Lisp-level name of the variable.
+@item vname
+The C-level name of the variable.
+@item doc
+The documentation for the variable, as a C comment.
+@end table
+
+  By convention, when defining variables of a ``native'' type
+(@code{int} and @code{bool}), the name of the C variable is the same
+as the name of the Lisp variable with ``-'' replaced by ``_''.  When
+the variable can hold any Lisp object, the convention is
+to also prefix the C variable name with ``V''.  i.e.
+
+@smallexample
+DEFVAR_INT ("my-int-variable", my_int_variable,
+           doc: /* An integer variable.  */);
+
+DEFVAR_LISP ("my-lisp-variable", Vmy_lisp_variable,
+           doc: /* A Lisp variable.  */);
+@end smallexample
+
+If you want to define a constant symbol rather than a variable, use
+@code{DEFSYM} instead.  e.g.
+
+@smallexample
+DEFSYM ("Qmy_symbol", "my-symbol");
+@end smallexample
+
 @cindex defining customization variables in C
   If you want to make a Lisp variable that is defined in C behave
 like one declared with @code{defcustom}, add an appropriate entry to