Finding Success (and Failure) in Haskell

Handling one failed check is straightforward. Giving someone a useful account of every problem is more interesting—and that practical challenge gives this Haskell book its shape. Julie Moronuki and Chris Martin build a small input-validation program step by step, using it to make ideas such as Maybe, Either, Monad, and Applicative concrete.

Learn Haskell by improving one working example

The book starts with conditionals and case expressions, then develops functions for checking passwords and usernames. As the example grows, the authors refactor it with different types and approaches to failure. Rather than introducing abstractions in isolation, the lessons show where each one enters the program and what it makes possible.

From the first check to better error messages

Successive chapters explore validation, newtypes, type constructors, and the relationship between monadic and applicative styles. A central thread is the difference between stopping when the first check fails and collecting multiple errors—an especially useful distinction when designing input forms or other checks that should report more than one problem at a time.

A practical route into functional concepts

Exercises invite readers to try the ideas themselves, with solutions and reference material included later in the book. The emphasis is on understanding by doing, with relatively little assumed Haskell experience and explanations introduced as the running example needs them.

Who may find it useful?

This is a good fit for newer Haskell programmers who want a guided, code-centered introduction, and for readers who have encountered monads or applicatives but want to see how they affect a real program. Bring a compiler, follow the example, and watch a small validation task open the door to larger ideas.