[masak]

The (old) MIX programs in The Art of Computer Programming by Knuth were often self-modifying, in the sense that they modified jump addresses at the end of routines to return to the right caller. (That is, they set the address to right after the call.)

The book chose that way to do it because it was standard practice at the time. It quickly fell out of fashion, though. Nowadays, we do it with a call stack, and each stack frame holds a return address. (Which is better anyway, since it allows routines to be re-entrant.)

The newer MMIX architecture (in some of the newer books) don't rely on such self-modification.