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A monad in programming is a composable computation description. Monads are an important construct in functional programming languages like Haskell.

A monad in programming is a composable computation description. Monads are an important construct in functional languages like Haskell.

In Haskell, a Monad is simply any type m with two functions following several algebraic laws:

return :: a -> m a
(>>=) :: m a -> (a -> m b) -> m b


These types can be used for a wide variety of different tasks including: IO, continuations, coroutines, non-determinism, error-handling, mutable state and even parsing. In addition, they are particularly useful for embedding simple DSLs within a functional language like Haskell.