https://github.com/codewitheshayoutube/content-free-grammar-project

https://github.com/codewitheshayoutube/content-free-grammar-project

Last synced: about 1 month ago
JSON representation

• Host: GitHub
• URL: https://github.com/codewitheshayoutube/content-free-grammar-project
• Owner: codewithEshaYoutube
• License: apache-2.0
• Created: 2025-04-27T09:25:47.000Z (about 1 year ago)
• Default Branch: main
• Last Pushed: 2025-05-13T15:27:33.000Z (about 1 year ago)
• Last Synced: 2025-05-13T16:44:18.419Z (about 1 year ago)
• Language: Python
• Size: 13.7 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE
  • Codeowners: .github/CODEOWNERS

Awesome Lists containing this project

README

          
# 📘 Context-Free Grammar (CFG) in Automata — Python Code Example

This guide explains **Context-Free Grammar (CFG)** in Automata theory and shows how to implement a parser in Python using the `lark` library.

---

```python

# 📄 What is CFG?

# CFG stands for Context-Free Grammar.

# It defines the syntactic rules for a language using recursive productions.

# A CFG is a 4-tuple: G = (V, Sigma, R, S)

# - V: Set of variables (non-terminal symbols)

# - Sigma: Set of terminals (input alphabet)

# - R: Set of production rules

# - S: Start symbol

# 📄 Example: CFG for Balanced Parentheses

# V = {S}

# Sigma = {(, )}

# R:

#   S → (S)

#   S → SS

#   S → ε (empty string)

# This grammar generates:

# "", "()", "(())", "()()", "(()())", etc.

# 📦 Step 1: Install the required library

# Run this in your terminal if not already installed:

# pip install lark

# 🧠 Step 2: Python Code Implementation

from lark import Lark

# Define CFG grammar using Lark syntax

cfg_grammar = """

    start: expr

    expr: "(" expr ")"        -> parens

        | expr expr           -> concat

        |                     -> empty

"""

# Create a parser for the grammar

parser = Lark(cfg_grammar, start='start')

# Test input strings for validation

test_strings = ["", "()", "(())", "()()", "(()())", "(()", "())("]

# Check each string and print whether it is valid

for s in test_strings:

    try:

        parser.parse(s)

        print(f"✔ '{s}' is VALID")

    except:

        print(f"✘ '{s}' is INVALID")

# 📄 Output:

# ✔ '' is VALID

# ✔ '()' is VALID

# ✔ '(())' is VALID

# ✔ '()()' is VALID

# ✔ '(()())' is VALID

# ✘ '(()' is INVALID

# ✘ '())(' is INVALID

# ✅ Summary:

# This script demonstrates how to use a context-free grammar to validate

# balanced parentheses using the `lark` library in Python.