Now that you’ve learned about pattern matching, you’ll discover partial functions and how they relate to pattern matching in this lesson. Partial functions are functions that are defined only for some input. You’ll see how they can be useful to abstract commonalities between functions and how you can compose them to create more complex functionalities. Finally, you’ll see how you can use partial functions to catch and handle exceptions. In the capstone, you’ll use partial functions to define the routes of your HTTP server.
Suppose you need to compute operations on integers. In particular, you want to calculate the square root of an integer. But this operation is defined only for nonnegative numbers. When dealing with a negative integer, you need to either return the negative value or return zero, depending on your use case. You could use pattern matching and define two functions.