Functional programming není jen akademický koncept. Pure functions, immutability a composition vedou k čistějšímu kódu.

Klíčové principy¶

• Pure functions: Stejný vstup → stejný výstup, žádné side effects
• Immutability: Data se nemění, vytváří se nová
• First-class functions: Funkce jako hodnoty
• Composition: Skládání malých funkcí

Practical Examples¶

Python — map, filter, reduce¶

from functools import reduce numbers = [1, 2, 3, 4, 5] doubled = list(map(lambda x: x * 2, numbers)) evens = list(filter(lambda x: x % 2 == 0, numbers)) total = reduce(lambda a, b: a + b, numbers)

List comprehension (pythonic)¶

doubled = [x * 2 for x in numbers] evens = [x for x in numbers if x % 2 == 0]

Composition¶

from functools import reduce def compose(*fns): return reduce(lambda f, g: lambda x: f(g(x)), fns) process = compose(format_output, validate, parse_input) result = process(raw_data)

JavaScript FP¶

const users = [{ name: ‘Jan’, age: 30 }, { name: ‘Eva’, age: 25 }]; const names = users.map(u => u.name); const adults = users.filter(u => u.age >= 18); const totalAge = users.reduce((sum, u) => sum + u.age, 0); // Immutability const updated = { …user, age: 31 }; // Spread, ne mutace const newList = […items, newItem];

Key Takeaway¶

Pure functions pro testovatelnost, immutability pro prediktabilitu, map/filter/reduce místo for loops.