The Science of Functional Programming, Part I: A tutorial, with examples in Scala

This book is a pedagogical in-depth tutorial and reference on the functional programming paradigm. Starting from issues found in practical coding, the book builds up the theoretical intuition, knowledge, and techniques that functional programmers use for for rigorous reasoning about types and code. The first part of the book focuses on working with collections; recursive functions and types; higher-order functions; and the Curry-Howard correspondence. Detailed explanations and derivations are accompanied by solved examples tested in the Scala interpreter, as well as exercises and discussions that further build upon each chapter's material. The difficulty of this book's mathematical material is at the level of undergraduate multivariate calculus.