17.3 Finite-State Automata We have seen how regular expressions can be used to generate languages mechanically. How might languages be recognized mechanically? The question is of interest because if we can mechanically recognize languages like all legal C++ programs that will not go into infinite loops on any input, then it would be possible to write uber-compilers that can do semantic error-checking like testing for infinite loops, in addition to the syntactic error-checking they currently do.