In Parts 1 and 2 you learned the basics of pure evaluation and how it helps in parallelizing and distributing code. However, sometimes you need to step out to the wild world of side effects. You’ll start by looking at simple input and output in Haskell. At the beginning, the information will be input in the console, and the output will be printed on the screen. Afterward, you’ll learn how to use a permanent means of storing data and reading and writing from files in disk.
Computations with side effects may turn out wrong in many ways; maybe the data ...
