FIRST AND FOLLOW LL(1) STEP BY STEP

🔤 FIRST & FOLLOW Calculator

15 Grammar Examples • Step-by-Step • Animated Learning

📖 FIRST and FOLLOW — First Understand

🔵 FIRST

FIRST(X) is the set of terminals that can appear at the beginning of strings derived from X.

FIRST(X) = Possible starting terminals

🟣 FOLLOW

FOLLOW(A) is the set of terminals that can appear immediately after the non-terminal A.

FOLLOW(A) = Symbols occurring after A

⚪ Epsilon

The symbol ε means the empty string. If a symbol can generate ε, we may need to examine the next symbol.

💲 End Marker

The symbol $ represents the end of the input. For the start symbol:

$ ∈ FOLLOW(Start Symbol)

📚 Important Rules

FIRST Rule 1

If X is a terminal:

FIRST(X) = {X}

FIRST Rule 2

For A → aα:

a ∈ FIRST(A)

FOLLOW Rule 1

For the start symbol:

$ ∈ FOLLOW(S)

FOLLOW Rule 2

For A → αBβ:

FIRST(β) − {ε} ⊆ FOLLOW(B)

🎓 15 Practice Examples

Example 1 — S → aA | bB Example 2 — S → AB Example 3 — S → ABC Example 4 — S → aS | b Example 5 — S → (S)S | ε Example 6 — Expression Grammar Example 7 — Epsilon Grammar Example 8 — Arithmetic Grammar Example 9 — Simple Assignment Example 10 — Nested Expression Example 11 — Multiple Epsilon Example 12 — Boolean Grammar Example 13 — List Grammar Example 14 — Statement Grammar Example 15 — Complex LL(1)

Example 1 of 15

Example 1

Grammar

S → aA | bB A → c B → d

🔎 Step-by-Step Calculation

✅ Final FIRST & FOLLOW

🎬 Animated FIRST → FOLLOW Visualization

📜
Grammar

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🔵
FIRST

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⚪
Check ε

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🟢
FOLLOW

Press "Animate" to start

FIRST / FOLLOW

📋 15 Examples — Quick Reference

No.	Grammar Type	Main Concept
1	Simple Grammar	Basic FIRST
2	A → a | ε	Epsilon
3	S → ABC	Multiple Symbols
4	S → aS | b	Recursion
5	S → (S)S | ε	Balanced Structure
6	Expression Grammar	FIRST/FOLLOW
7	Epsilon Grammar	Propagation
8	Arithmetic Grammar	LL(1)
9	Assignment	Terminal After NT
10	Nested Expression	Nested FOLLOW
11	Multiple Epsilon	Epsilon Propagation
12	Boolean Grammar	Logical Operators
13	List Grammar	Repeated Elements
14	Statement Grammar	Parser Design
15	Complex LL(1)	Complete Revision

⭐ Why FIRST and FOLLOW Are Important?

1️⃣ LL(1) Parser

FIRST and FOLLOW are fundamental for constructing LL(1) predictive parsing tables.

2️⃣ Production Selection

They help the parser select the correct production for a given input symbol.

3️⃣ ε Productions

FOLLOW helps determine when an ε-production should be selected.

4️⃣ Syntax Analysis

They are important concepts in the syntax-analysis phase of compiler design.

🌟 Created by Bijan Krishna Paul 🌟
B.K.PAUL Bhairab Ganguly College