What is the main idea of functional programming?

The main idea of functional programming is to build programs as compositions of pure functions, which is achieved by eliminating mutable state and side effects.

Key concepts:

• Pure functions: Functions that always return the same result for the same inputs and do not cause side effects (changes outside the function, input/output).
• Immutability: Data cannot be changed after creation. Instead, a new version of the data is created.
• First-class functions: Functions can be assigned to variables, passed as arguments to other functions, and returned as results.
• Function composition: Combining simple functions to create more complex ones.

Advantages:

• Improved testability and predictability of code.
• Simplification of parallel and multithreaded execution due to the absence of state.
• Reduction in errors related to mutable state.
• Code becomes more declarative and easier to understand (what to do, not how to do it).