Functional Programming explained to my grandma

Anne-Honyme

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Currying

Currying is one of the words you will hear the most when you start to work with functional programming. It is also one of the hardest to figure out.

Definition: Currying is the technique of translating the evaluation of a function which takes multiple arguments into evaluating a sequence of functions, each with a single argument *

We can see currying as a series of partial application.

For a function who has N parameters, a partial application will have N-X. It improves code readability by binding some parameters and giving names to specific uses.

Implement the area computation

package example
/**
  * Created by charlotte on 15/06/17.
  */
object Area {
  def area(x : Double, y:Double):Double =(x, y) match { // it's pattern matching
      // you can use it to define some differents implementations
      // as a function of the parameters
    case (_, math.Pi) => x*x*math.Pi // for example here you can define a specific implementation for circles
    case (_, _) if x>0 && y>0 => y*x //and another one for rectangle
  }
  def circleArea(radius: Double): Double= ??? //TODO Compute the circle area using the existing method
  def squareArea(side: Double): Double= ??? //TODO Compute the square area using the existing method
  //let's create circleArea and squareArea from the area function
}

Now we have seen what is partial application, we can introduce currying as a series of partial application, where at each step we only apply one parameter.

Example

Implement the multiply and multiplyByTwo

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