Functional Programming in Scala

curry_1.scala

//Currying is when you break down a function that takes multiple arguments into a //series of functions that take part of the arguments.
//converts a function f of two arguments into a function of one argument that partially applies f.
  def curry[A,B,C](f: (A,B) => C): A => (B => C) =
  		(a: A) => (b: B) => f(a,b)  
  //> curry: [A, B, C](f: (A, B) => C)A => (B => C)

loop_1.js

//in javascript

//A loop - prints "1 2 3" to console
var res = 0
let nums = [1, 2, 3]
for(i=0; i<nums.length; i++) {
	res = res + nums[i]
}

//Another loop - Performs 1+2+3 then print out sum
var res = ""
let strs = ["a", "b", "c"]
for(i=0; i< strs.length; i++) {
	res = res + strs[i]
}

loop_2.js

[1,2,3].reduce((a,b) => (a+b), 0) //> 6
["a", "b", "c"].reduce((a,b) => a+b, "") //> "abc"

loop_3.js

const myReduce = (arr, initVal) => 
	arr.reduce((a,b) => (a+b), initVal)

let arr1 = [1,2,3]
let arr2 = ["a", "b", "c"]
myReduce(arr1, 0) //> 6
myReduce(arr2, "") //>"abc"

loop_4.js

let arr3 = [arr1, arr2]
myReduce(arr3, [])

loop_5.js

let arr3 = [arr1, arr2]
arr3.reduce((a,b) => a.concat(b), [])

loop_6.scala

//In Scala
List(1,2,3) ++ List("a", "b", "c") //> res: List[Any] = List(1, 2, 3, a, b, c)

List(1,2,3) ++ "abc" //> res: List[AnyVal] = List(1, 2, 3, a, b, c)

"abc" ++ List(1,2,3) //res: scala.collection.immutable.IndexedSeq[AnyVal] = Vector(a, b, c, 1, 2, 3)

"abc" ++ "def" //> res: String = abcdef
"abc" + "def" //> res: String = abcdef

monoid_1.js

//In javascript

let arr1 = [""]
let arr2 = ["", ""]
let arr3 = ["", "", "a"]

let res1 = arr1.reduce((a,b) => a+b) //> ""
let res2 = arr2.reduce((a,b) => a+b) //> ""
let res3 = arr3.reduce((a,b) => a+b) //> "a"

const strLen = arr => 
	arr.reduce((a,b) => a+b).length

strLen([res1]) //> 0
strLen([res1, res2]) //> 0
strLen([res1, res2, res3]) //> 1
strLen([res3, res2, res1]) //> 1

type_1.scala

def findAve(l: List[Double]): Double  = l.reduce(_ + _)/l.length
findAve(List(1,2,3))

type_2.js

//In javascript
let num = "7" //user inputs "7" for num
let res = num - 1 //> 6 ... good

let num = "07" //user inputs "07" for num
res = num - 1 //>6 ... still good

let num = "apple" - 1 //> NaN
res = num - 1 //> NaN ... bad

type_3.scala

def findAve(l: List[Double])  = l.reduce(_ + _)/l.length
//> findAve: (l: List[Double])Double

type_4.js

//In javascript
let findAve = arr => arr.reduce((a,b) => a+b)/arr.length

findAve([1,2,3]) //> 2
findAve([1,1,3]) //>1.6666666666666667

type_5.scala

//In Scala
def findAve(l: List[Int])  = l.reduce(_ + _)/l.length  
//> findAve: (l: List[Int])Int

findAve(List(1,2,3)) //> 2
findAve(List(1,1,3)) //> 1

def findAve2(l: List[Int]): Double  = l.reduce(_ + _)/l.length
findAve2(List(1,1,3)) //> 1.0

def findAve3(l: List[Double]): Double  = l.reduce(_ + _)/l.length
findAve: (l: List[Double])Double
findAve(List(1,1,3)) //>1.6666666666666667

why_1.java

//In Java
double[] arr = new double[] {1,2,3};
double acc = 0;
for(int i=0; i<arr.length; i++) {
	acc += arr[i];
}
double ave = acc/arr.length;

System.out.println("The average of " + Arrays.toString(arr) + " is "+ave);  
//> The average of [1.0, 2.0, 3.0] is 2.0

why_2.scala

//In Scala
def list = List(1.0, 2.0 ,3.0)
def findAve(l: List[Double]): Double  = l.reduce(_ + _)/l.length
findAve(List(1,2,3))

println(s"The average of $list is $ave") 
//> The average of List(1.0, 2.0, 3.0) is 2.0