Functional programming languages restrict mutable variables and assignments, instead focusing on functions. This makes programs more elegant and easier to distribute. Functional programming supports high-order functions where functions can be passed as parameters or returned as results. Recursion in functional programming uses tail recursion to avoid stack overflows. Loops can be thought of as functions applied to collections, and many common looping tasks can be expressed using functions like filter, map, and reduce.

1. Functional Programming

2. Idea
• Restricted sense, a functional programming
language is one which does not have mutable
variables, assignments, or imperative control
structures.
• Wider sense, a functional programming
language enables the construction of elegant
programs that focus on functions. So it will be
easier to be distributed

3. High-order funtion
• Function
– as paramters
– as result
=> Currying : f(x,y) => z = g(x)(y) => z

4. Quiz
//greatest common divisor of two numbers
def gcd(a:Int, b:Int): Int =
if (b==0) a else gcd(b, a%b)
//factorial number
def factorial(n:Int): Int =
if (n==0) 1 else n*factorial(n-1)
What is different between recursion call of gcd and
factorial

5. Tail recursion
• “If a function calls itself as its last action, the
function’s stack frame can be reused”
=> Never be stackoverflow again with recursion
• All recursion can be rewrite to tail recursion

6. Exercise 1
• Rewrite factorial as tail-recursion

7. Think about loop in different way
• Basically for loop = f(c) with c is a collection

8. Think about loop in different way (2)
Does a string have an uppercase character
Java
Scala

9. Think about loop in different way (3)
Return all even member of a collection and time 2
Java : Cannot fit this slide (shame on you, java)
Scala
val rs = input.filter(_%2==0).map(_*2)

10. Think about loop in different way (4)
• exists
• filter
• find
• forall
• foreach
• map
• reduce