FRP – the map() function Marble diagram

In Scala, the map() function performs the following steps one by one:

1. Take each element from the source container.
2. Apply the given function.
3. Create a new container of the same type as the destination container. Here, container means any data structure that can hold more than one element; for instance, a Collection, Option, Either, and so on.

In the Reactive World, we can call this container a data stream, as it emits or consumes the data (or data elements).

Here's the Scala sample code for the map() function:

scala> val numList = List(1,2,3,4,5) 
numList: List[Int] = List(1, 2, 3, 4, 5) 
 
scala> val squaredNumList = numList.map( x => x*x ) 
squaredNumList: List[Int] = List(1, 4, 9, 16, 25) 

Here, the map() function picks up each element from a number list, squares it, and creates a new list with the resultant numbers. Let's represent this map() functional operation in a pictorial form using a Marble diagram:

Here, the source data stream is a List (1,2,3,4,5) and the destination or resulting data stream is also a list with the squared value, that is, List (1, 4, 9, 16, 25).

The data transformation or functional operator is map( x => x*x ).