Lua console with debug.traceback() available as a global

main.c

#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>

// from https://www.lua.org/pil/24.2.3.html
static void stackDump(lua_State *L) {
	int i;
	int top = lua_gettop(L);
	for (i = 1; i <= top; i++) {  /* repeat for each level */
		int t = lua_type(L, i);
		switch (t) {

		case LUA_TSTRING:  /* strings */
			printf("`%s'", lua_tostring(L, i));
			break;

		case LUA_TBOOLEAN:  /* booleans */
			printf(lua_toboolean(L, i) ? "true" : "false");
			break;

		case LUA_TNUMBER:  /* numbers */
			printf("%g", lua_tonumber(L, i));
			break;

		default:  /* other values */
			printf("%s", lua_typename(L, t));
			break;

		}
		printf("  ");  /* put a separator */
	}
	printf("\r\n");  /* end the listing */
}

// modified interactive Lua console from https://www.lua.org/pil/24.1.html
int main()
{
	char buff[256];
	int error;
	int ret;
	lua_State *L = luaL_newstate();

	// Load some of the standard library
	luaL_requiref(L, "_G", luaopen_base, 1);
	luaL_requiref(L, "math", luaopen_math, 1);
	luaL_requiref(L, "package", luaopen_package, 1);
	luaL_requiref(L, "table", luaopen_table, 1);
	luaL_requiref(L, "string", luaopen_string, 1);
	lua_pop(L, 5); // luaL_requiref leaves a copy of the module table on the stack; pop those tables

	// Store the debug.traceback() function as a global, without the rest of the debug library available
	luaopen_debug(L); // stack now contains: debug table
	stackDump(L);

	ret = lua_getfield(L, -1, "traceback"); // stack now contains: debug table, traceback fn
	assert(LUA_TFUNCTION == ret);
	stackDump(L);

	lua_setglobal(L, "traceback"); // stack now contains: debug table
	stackDump(L);

	lua_pop(L, 1); // stack is now empty

	while (printf("> ") && fgets(buff, sizeof(buff), stdin))
	{
		error = luaL_loadbuffer(L, buff, strlen(buff), "line") || lua_pcall(L, 0, 0, 0);

		if (error)
		{
			fprintf(stderr, "%s\n", lua_tostring(L, -1)); 
			lua_pop(L, 1); /* pop error message from the stack */
		}
	}
}