an alternative: hooks for addons

[dws@cs.wisc.edu (DaviD W. Sanderson)]

Here is an alternative proposal.  I suggest adding hooks to builtin.c
to allow for locally-defined builtins.  It would be really easy to do.

There would be two new source files: addon.h and addon.c

------ addon.h -------
/*
 * This file is the interface to the rest of rc for any locally
 * defined addon builtins.
 * The interface consists of the following macros.
 *
 * ADDON_FUN	A comma-separated list of the function names for the
 *		builtins.
 *
 * ADDON_STR	A comma-separated list of string literals corresponding
 *		to the function names in ADDON_FUN.
 *
 * The addon functions must also have proper prototypes in this file.
 * The builtins all have the form:
 *
 *	void b_NAME(char **av);
 *
 * Builtins report their exit status using set(TRUE) or set(FALSE).
 *
 * Example:
 *
 *	#define ADDON_FUN	b_access, b_printf
 *	#define ADDON_STR	"access", "printf"
 */

#define ADDON_FUN	/* nothing */
#define ADDON_STR	/* nothing */
------ addon.h -------

------ addon.c -------
/*
 * This file contains the implementations of any locally defined
 * builtins.
 */

#include "rc.h"		/* for boolean TRUE, FALSE */
#include "status.h"	/* for set() */
#include "addon.h"

static char dummy;	/* prevent an "empty translation unit" */
------ addon.c -------

Then builtins.c would be modified to #include "addon.h".
The definitions of the builtins[] and builtins_str[] arrays would
simply be augmented to:

static builtin_t *const builtins[] = {
	b_break, b_builtin, b_cd, b_echo, b_eval, b_exec, b_exit,
	b_limit, b_return, b_shift, b_umask, b_wait, b_whatis, b_dot
	, ADDON_FUN
};

static char *const builtins_str[] = {
	"break", "builtin", "cd", "echo", "eval", "exec", "exit",
	"limit", "return", "shift", "umask", "wait", "whatis", "."
	, ADDON_STR
};

This would work because the code doesn't do anything fancy like
a binary search to find the builtins.
Even adding these hooks would probably offend the zealots, but I don't
think they would stop using rc because of it.  After all, there are
already (considerably more elaborate) hooks for readline().

If this were done then I could easily add the builtins I wanted to my
own private copy of rc without offending anyone.  Also, the presence of
such builtins could be detected easily via whatis.

DaviD Sanderson