Recursive Streams and collection in Scala

Recursive forms have their definition in terms of themselves like we have subfolders in folders which can further have subfolders. Recursive methods calling themselves is also a recursive form. Similar forms can be used to create a recursive stream. Example 1: Creating a lazy list 

Output : 

Stream(1, ?)
1
5

In the code above the second con can be recursive. Example 2: Create a lazy list by placing a recursive call to method 

Output : 

Stream(5, ?)

Example 3: Create a lazy list by placing a recursive call to method in a brief and clear manner 

Output : 

Stream(5, ?)

Stream Collections

Stream collections in scala are very important as it allows need not to be explicitly lopped over. Declaratively things can be performed using functional combinators like map, filter, and flatMap. Streams are lazy lost collections. Example 4: 

Output : 

Stream(0, ?)
0 ; 1 ; 2 ; 3 ; 4 ; 5 ; 6 ; 7 ; 8 ; 9)

Example 5: Using filter 

Output :

List(3, 4)

filter is called over the list geek. It takes function as an argument and returns a Boolean, which is a function predicate. Every element is run through the function and elements are filtered out where the function returns false. It results in a new list and the original "geek" list is remain persistent. Example 6: Using filter in a much concise manner 

Output :

List(3, 4)

In the code above, there is no need to name the element. The element is referred by a shorter form via a_. Also there is no need to qualify the method call.