Swift!BASIC lets the experienced programmer extend the language by making calls to the operating system of the computer. The SYSTEM() command in Swift!BASIC is very well implemented and easy to use. The downside to this is that you need to know exactly what you're doing. A good book on MS-DOS internal functions (interrupts) will help get you started. It will take some trial and error, and several system crashes, before you get the hang of this feature.
In addition to DOS, the HP 95LX has another operating environment: SYSMGR. Swift!BASIC handles calls to this operating environment as adroitly as it handles calls to DOS and the BIOS. However, the same admonition applies; you've got to know exactly what you're doing. You must also have the HP Independent System Developers' Manual to incorporate such features as "clipboard" and "menu" in your programs. (See sidebar, page 43 of the Fall 91 issue for more information.)
For really experienced BASIC programmers, there's nothing like the thrill of POKE-ing hex numbers into memory. This is the way to get the computer to "sing and dance" (or crash and burn quickly). Swift!- BASIC provides this capability as well. It is one of the more dangerous capabilities of any BASIC interpreter and should only be used if you've backed up everything in sight.