Monad (functional programming)

In functional programming, a monad is a design pattern that allows structuring programs generically while automating away boilerplate code needed by the program logic.Monads achieve this by providing their own data type, which represents a specific form of computation, along with one procedure to wrap values of any basic type within the monad (yielding a monadic value) and another to compose functions that output monadic values (called monadic functions). In functional programming, a monad is a design pattern that allows structuring programs generically while automating away boilerplate code needed by the program logic.Monads achieve this by providing their own data type, which represents a specific form of computation, along with one procedure to wrap values of any basic type within the monad (yielding a monadic value) and another to compose functions that output monadic values (called monadic functions). This allows monads to simplify a wide range of problems, like handling potential undefined values (with the Maybe monad), or keeping values within a flexible, well-formed list (using the List monad).With a monad, a programmer can turn a complicated sequence of functions into a succinct pipeline that abstracts away auxiliary data management, control flow, or side-effects. Both the concept of a monad and the term originally come from category theory, where it is defined as a functor with additional structure.Research beginning in the late 1980s and early 1990s established that monads could bring seemingly disparate computer-science problems under a unified, functional model.Category theory also provides a few formal requirements, known as the monad laws, which should be satisfied by any monad and can be used to verify monadic code. Since monads make semantics explicit for a kind of computation, they can also be used to implement convenient language features.Some languages, such as Haskell, even offer pre-built definitions in their core libraries for the general monad structure and common instances. 'For a monad m, a value of type m a represents having access to a value of type a within the context of the monad.' —C. A. McCann