A celebration of pure functional programming.
Haskell embodies the conviction that programming can be a mathematical discipline — that functions are first-class citizens, that side effects must be declared, that laziness is a virtue. Born from the collective will of researchers who believed that a purely functional language could change how we reason about computation, Haskell has become the laboratory where ideas about type systems, monads, and category theory are tested, refined, and proven elegant.
In Haskell, every expression has a type. Every type tells a story. And every program is, at its heart, a proof.
map :: (a -> b) -> [a] -> [b]
The quintessential higher-order function. map takes a function that
transforms values of type a into values of type b, applies it to
every element of a list, and returns the transformed list. It is the fundamental
operation of functors — the bridge between structure and transformation.
(>>=) :: Monad m => m a -> (a -> m b) -> m bThe monadic bind operator — the engine of sequential computation in Haskell. It takes a monadic value and a function that produces a new monadic value, chaining them together. This is how Haskell sequences effects while maintaining purity: not by abandoning functional principles, but by encoding sequentiality in types.
foldr :: (a -> b -> b) -> b -> [a] -> b
The right fold — a universal operator from which all list-processing functions
can be derived. It replaces the structural constructor of a list with a combining
function, collapsing a list into a single value. In Haskell, foldr is
lazy: it can operate on infinite lists, producing results incrementally.