Follow and First of compilation principles

Given that the grammar in the book is too advanced, I have summarized the following methods to ensure that you will be able to learn it as soon as you learn it!

I would like to thank you, Mr. Zhang feiqing. Without your help, I will not be able to do it today. Haha !!

Example 4.6 for grammar g (E)

E → te'

E' → + Te | E ε

T → ft'

T → * ft 'hour | E ε

F → (e) | I

Construct the first and follow sets of each non-Terminator:

First (e) = {(, I}

First (e ') = {+, ε}

First (t) = {(, I}

First (t') = {*, ε}

First (f) = {(, I}

Follow (e) = {),#}

Follow (E Branch) = {),#}

Follow (t) = {+ ,),#}

Follow (T Branch) = {+ ,),#}

Follow (f) = {*, + ,),#}

Now!

The first is the first set:

This is relatively simple, that is, it is always deduced until a Terminator is found! Note that you only need to check the first character on the right of each generative formula.

The focus is on the follow set:

First, you must know that the folllow set is performed in the right part of the production formula.

1: Find the non-Terminator that requires the follow set in the right of the production formula.

2: Check whether the required non-Terminator is the start character. If yes, add # To the follow set.

2: check whether there are any characters after this Terminator. Are you sure you want to find it? I can't speak anymore!

3: The following is an if condition judgment.

If (not followed by characters)

{

Add the follow set of non-terminator in the right part of the formula to the desired set;

}

Else (with characters)

{

Evaluate the first set for this character first;

If (this character can be deduced to ε)

{

Calculate the follow set of this character;

}

}

4: Done!

Haha, my first learning experience is actually the worst compilation principle I have learned.