Learn Haskell Fast and Hard

Abstraction: Dense Haskell tutorial from basics through monads and IO

Key points:

• Haskell is purely functional, statically typed with inference, lazy by default, and enforces purity — side effects only in IO a typed functions
• Type classes (like Num) enable parametric polymorphism — one function works across all numeric types without C-style per-type duplication
• Pattern matching, higher-order functions (map, foldl, filter), eta-reduction, and function composition ((.)) are core idioms
• IO monad explained as threading a World state parameter; >>= (bind) eliminates explicit temporary world variables
• Maybe monad cleanly sequences computations that can fail, replacing deeply nested if/else chains
• Laziness enables infinite data structures (e.g., infinite binary trees) evaluated only as needed

Connections: Haskell · Ghc · Functional Programming · Type Systems · Monads

Source: http://yannesposito.com/Scratch/en/blog/Haskell-the-Hard-Way/