BartoszMilewski - Composition is the Essence of Programming - Challenges

gistfile1.scala

object Category {

  
  //Implement, as best as you can, the identity function in your favorite language
 // (or the second favorite, if your favorite language happens to be Haskell).
      def id[A]( a:A ):A=a;                     //> id: [A](a: A)A
   
      
      
  //Implement the composition function in your favorite language.
  // It takes two functions as arguments and returns a function that is their composition.
    def compose[A,B,C] ( f:A=>B , g:B=>C ):(A=>C)= x=> g(f(x)); // g.apply(f(x));    you get a function that takes A and returns C

    
    
  //Write a program that tries to test that your composition function respects identity.
  def testFunc(a:Int):Int=a+1                        //> testFunc: (a: Int)Int
  def h=compose[Int,Int,Int]( id,testFunc)          //> h: => Int => Int
  def h1=compose[Int,Int,Int]( testFunc,id)        //> h1: => Int => Int
  
  
  h(4)                                            //> res0: Int = 5
  h1(4)                                           //> res0: Int = 5      
}