functional programming

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