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Declarative Programming

Declarative programming is a paradigm that focuses on what the program should accomplish rather than how to accomplish it.

Core Concept​

Key Characteristics​

  • Express logic without describing control flow
  • Focus on the end result
  • Let the system figure out execution
  • Higher level of abstraction

Examples​

SQL (Declarative)​

-- Declarative: What we want
SELECT name, age 
FROM users 
WHERE age > 18 
ORDER BY name;

-- System figures out HOW to retrieve data

HTML/CSS (Declarative)​

<!-- What we want to display -->
<div class="card">
    <h1>Title</h1>
    <p>Content</p>
</div>

<style>
.card {
    padding: 20px;
    background: white;
    border-radius: 8px;
}
</style>

React (Declarative UI)​

function UserList({ users }) {
    return (
        <ul>
            {users.map(user => (
                <li key={user.id}>{user.name}</li>
            ))}
        </ul>
    );
}

Advantages​

✅ More Readable: Intent is clear
✅ Less Error-Prone: No manual control flow
✅ Optimizable: System can optimize execution
✅ Higher Abstraction: Focus on business logic

When to Use​

  • Database queries (SQL)
  • Configuration files (YAML, JSON)
  • UI layouts (HTML/CSS)
  • Build specifications (Make, Gradle)
  • Rule engines

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