added ';' at the end of "expression lines" ("return exp;") so that

an extra ";" at the end is enough to stop Lua printing the result
("return exp;;" is not valid)

lua.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lua.c,v 1.224 2015/03/10 14:15:06 roberto Exp roberto $
+** $Id: lua.c,v 1.225 2015/03/30 15:42:59 roberto Exp roberto $
 ** Lua stand-alone interpreter
 ** See Copyright Notice in lua.h
 */
@@ -324,24 +324,20 @@ static int pushline (lua_State *L, int firstline) {
 
 
 /*
-** Try to compile line on the stack as 'return <line>'; on return, stack
+** Try to compile line on the stack as 'return <line>;'; on return, stack
 ** has either compiled chunk or original line (if compilation failed).
 */
 static int addreturn (lua_State *L) {
-  int status;
-  size_t len; const char *line;
-  lua_pushliteral(L, "return ");
-  lua_pushvalue(L, -2);  /* duplicate line */
-  lua_concat(L, 2);  /* new line is "return ..." */
-  line = lua_tolstring(L, -1, &len);
-  if ((status = luaL_loadbuffer(L, line, len, "=stdin")) == LUA_OK) {
-    lua_remove(L, -3);  /* remove original line */
-    line += sizeof("return")/sizeof(char);  /* remove 'return' for history */
+  const char *line = lua_tostring(L, -1);  /* original line */
+  const char *retline = lua_pushfstring(L, "return %s;", line);
+  int status = luaL_loadbuffer(L, retline, strlen(retline), "=stdin");
+  if (status == LUA_OK) {
+    lua_remove(L, -2);  /* remove modified line */
     if (line[0] != '\0')  /* non empty? */
       lua_saveline(L, line);  /* keep history */
   }
   else
-    lua_pop(L, 2);  /* remove result from 'luaL_loadbuffer' and new line */
+    lua_pop(L, 2);  /* pop result from 'luaL_loadbuffer' and modified line */
   return status;
 }