monadlike

Monadlike is a term used in programming and theory to describe structures that resemble monads without necessarily being true monads. In functional programming, a monad is an endofunctor equipped with two operations, typically called unit (or return) and bind (or flatMap), which satisfy three laws: left identity, right identity, and associativity. Monadlike designs imitate this pattern by providing a way to wrap values, chain computations, and sequence effects, but they may not implement the full monadic interface or satisfy all laws.

In practice, monadlike constructs often offer a subset of monadic capabilities. They may support operations that resemble map and bind, or provide a wrapping type plus a mechanism to compose operations. However, they may permit deviations from the monad laws for reasons of performance, simplicity, or practical side effects. As a result, calling such constructs monads can be misleading in a strict mathematical sense, even though they enable similar programming workflows.

Common examples discussed as monadlike include optional or nullable types, which wrap a value and allow chaining while propagating absence; result or either types used for error propagation; and asynchronous handles like promises in languages that treat asynchronous steps as chained computations. In some ecosystems, these patterns are treated as monads in a pragmatic sense, while in others they are described as monadlike due to imperfect law adherence or limited law guarantees.

Related concepts include functors, applicative functors, and true monads. The term is often a descriptive label used to acknowledge monadic influence without asserting formal monadhood.