Level 2 — Intermediate

These lessons cover higher-order functions, folds, algebraic data types, records, Maybe and Either, type classes, Functor, Foldable, Applicative and Monad, IO and do-notation, laziness, modules, Data.Map and Data.Set, error handling, text and files, and cabal and Stack projects. Recommended: the Level 1 lessons, especially pattern matching, recursion, and lists.