This book provides an introduction to functional programming in Haskell:

• Functional Programming (FP) is one of the main programming paradigms, along with imperative programming and object-oriented programming. It uses functions as its core concept of computation – turning input into output in a predictable and context-independent way.While many non-FP languages also offer functions in some form, in FP, language functions truly have first-class status. They are not only computation but also data, which can be ferried around by other (higher-order) functions, dynamically assembled out of simpler functions, stored in data structures, or data containers themselves.
• Haskell stands out among FP languages in that it unequivocally embraces the FP paradigm. Because it does not make any compromises for imperative programming, Haskell had to come up with entirely new solutions to tackle common programming problems that also turned out to be successful in solving next-level problems. This way, it has become an inspiration for the designers of other programming languages (both FP and non-FP) and libraries in those languages.

Besides being true to the principles of FP, Haskell is also renowned for its sophisticated static type system. This means that Haskell programs are automatically checked for particular kinds of mistakes (known as type errors) before they are run. Moreover, thanks to Haskell’s powerful type inference mechanism, programmers have to write little to no type annotations themselves. Taking all the preceding aspects of FB in Haskell into consideration, the common theme of this book is abstraction. It provides many mechanisms for abstraction and powerful examples of abstractions that allow us to converse and reason about common programming patterns, becoming more effective programmers when we (re)use them.