Functional programming languages have several advantages over imperative languages like C/C++. They support type inference for improved simplicity and readability. Code is more concise due to features like higher-order functions, closures, and partial application. Immutable data structures also improve code quality. Abstract data types (ADTs) allow defining types like shapes that can be pattern matched, similar to object-oriented polymorphism but with advantages like algebraic properties. Functional patterns like chain of responsibility improve modularity.

1. Why FP
Elements of Functional languages

2. Type inference
•
Simplicity
•
Readability
•
Code economy

3. C/C++ example
int factorial(int n) {
return !n ? 1 : n * factorial(n - 1);
}

4. Haskell example
factorial :: Integer -> Integer
factorial n
| n < 0 = error «not defined»
| n == 0 = 1
| otherwise = n * fac (n - 1)

5. Haskell example
factorial n
| n == 0 = 1
| otherwise = n * fac (n - 1)

6. Haskell example
factorial n = product [1..n]

7. Higher-order function
(HOF)

8. Javascript example
_.sortBy([5,4,1,6], function(n){
return Math.sin(n)
})

9. Closure

10. Common Lisp example
(define counter-from
(lambda (n)
(lambda ()
(set! n (+ n 1))
n)))

11. Partial application

12. Python example
def partial(func, *args, **keywords):
def newfunc(*fargs, **fkeywords):
newkeywords = keywords.copy()
newkeywords.update(fkeywords)
return func(*(args + fargs),
**newkeywords)
newfunc.func = func
newfunc.args = args
newfunc.keywords = keywords
return newfunc

13. Immutable & persistent
data structures

15. ADT

16. OOP example
abstract class Shape {
abstract float area();
abstract void draw();
}
class Rectangle extends Shape {
float w, h;
...
float area() { return w * h; }
}
class Circle extends Shape {
float r;
...
float area() { return PI * r * r; }
}

17. ADT example
data Shape =
Rectangle Float Float
| Circle Float
area :: Shape -> Float
area (Rectangle w h) = w * h
area (Circle r) = pi * r * r
draw :: Shape -> IO ()
...

18. Compare
Rectangle
Circle
Other
area()
ADT
draw()
other()
OOP

19. Pattern matching

20. Haskell example
head (x:_) = x
tail (_:xs)= xs

21. Chain of responsibility

22. Abstract example
[recieve,
check,
process,
finish]