Mastering Functional Programming

Motivation and the imperative example

Consider the following example. Say you are developing a calendar application to compose a user's daily schedule. This application allows the user to write their plans for the Future into the database. For example, if they have a meeting with somebody, they can create a separate entry in the database, specifying when and where it will take place.

They may also want to add a weather forecast integration into the app. They would like to warn their users whenever they have outdoor activities in unfavorable weather conditions. For example, an outdoor picnic party is undesirable in rainy weather. One way to help the user avoid such situations is to make the application contact a weather forecast server and ...