State driven code is a good way to implement certain types of logic (parsers being an example). It can be done in several ways, for example:
State driving which bit of code is actually being executed at a given point (i.e. the state is implicit in the piece of code you are writing). Recursive descent parsers are a good example of this type of code.
State driving what to do in a conditional such as a switch statement.
Explicit state machines such as those generated by parser generating tools such as Lex and Yacc.
Not all state driven code is used for parsing. A general state machine generator is smc. It inhales a definition of a state machine (in its language) and it will spit out code for the state machine in a variety of languages.
