Another advantage is error recovery code can be made much better. Yacc and lex don't know what common errors are, but you as the language designer knows what th

Another advantage is error recovery code can be made much better. Yacc and lex don't know what common errors are, but you as the language designer knows what the most likely intention of the user was. Yacc/lex tend to produce generic error messages and do very poorly with error recovery.