The most important thing about BISON and YACC is that they generate a state machine which would parse exactly your grammar. This is for speed reason, since complexity of generated code is not O(n) with n = number of rules as it would be in most first-attempt implementations.

The state machine approach causes the number of states spawned to be very high and thus it would be very error prone to write that code. Manteinance of that code would also be an hell (where hell = I would leave the job if someone suggested me to do that).

Bison and Yacc make you concentrate on the grammar instead of its implementation.

The most important thing about BISON and YACC is that they generate a state machine which would parse exactly your grammar. This is for speed reason, since complexity of generated code is not O(n) with n = number of rules as it would be in most first-attempt implementations.

The state machine approach causes the number of states spawned to be very high and thus it would be very error prone to write that code. Manteinance of that code would also be an hell (where hell = I would quit the job if someone suggested me to do that).

Bison and Yacc make you concentrate on the grammar instead of its implementation.