Effective Haskell

Performing IO in a Pure, Lazy Language

Haskell’s approach to IO is different from other languages you might have worked with because, as a pure and lazily evaluated language, it has some constraints that don’t exist in other languages. Understanding the challenges that come with doing IO in a pure and lazy language is the first step to understanding how to do IO in Haskell. In this section, you’ll first learn about how purity and laziness present challenges to doing IO. After that, you’ll learn about IO and IO actions and how they address the challenges introduced by purity and laziness.

Understanding the Problems with IO

Laziness and purity are interesting and useful properties of Haskell, but they make IO particularly tricky. You learned about ...