If a function returns same value for the same argument every time, then the function is pure. That generally means that, the function cannot use any state values that could potentially change.

In OOP we treat data and functions separately. In FP, they are all the same. We can create an array of functions, pass a function as argument, return a function from a method.

Let's say there is a function that takes three arguments. Usually, we need to be aware of all three values to call this function, right? In partial application, the three arguments are provided at different times. I could not find a decent blog that explains this well. Here is the wikipedia page.

Recursion is when a function calls itself and an end condition exists in the function to stop the method call. We could talk about this in depth another day. For now, here is a good explanation.

This is a method where we take simple functions and combine them into a more complex function. Let's say we have two methods f(x) = x * 2 //(timesTwo) and f(x) = x - 1 // (minusOne) . And we want to compute f(x) = 2x -1 . You call the timesTwo function first. With the output of timesTwo , you call the minusOne function. How would you code this?

The requirement here is that the next function takes as argument the same type that the previous function returns.