Higher order functions are one of the key components of functional programming.

A higher order function is a tool that takes other functions as parameters or returns them as a result.

Blocks are nameless methods that can be passed to another method as a parameter.
Passing a block to a method is a great way of data abstraction.

Blocks can either be defined with a keyword do ... end or curly braces { ... }.

Example:

_{a). Passing a block to a method that takes no parameter}

_CODE

def call_block
    puts "Start of method."
    yield
    puts "End of method."
end 
call_block do 
    puts "I am inside call_block method."
end

_OUTPUT

Start of method.
I am inside call_block method.
End of method.

In this example, a block is passed to the call_block method.
To invoke this block inside the method, we used a keyword, yield.
Calling yield will execute the code within the block that is provided to the method.

_{b). Passing a block to a method that takes one or more parameters.}

_CODE

def calculate(a,b)
    yield(a, b)
end

puts calculate(15, 10) {|a, b| a - b}   

_OUTPUT

5

In this example, we have defined a method calculate that takes two parameters and .
The yield statement invokes the block with parameters and , and executes it.

Task

You are given a partially complete code. Your task is to fill in the blanks (_______).
The factorial method computes: n! { x x x }.