ThenValue

ThenValue is a concept used in promise-like and functional programming libraries to describe a continuation that processes the successful result of an asynchronous computation. In typical usage, if an asynchronous operation yields a value of type T, thenValue applies a function f: T -> U and returns a new asynchronous computation that delivers the result U. If the original computation fails, the error is propagated to the new computation.

The exact semantics of thenValue vary by library. In many cases, it behaves like a map operation: it takes a function that returns a plain value and produces a new asynchronous result without creating nested structures. In other contexts, if the function returns another monadic value, thenValue can act like a bind or flatMap, chaining computations and flattening the result. Some ecosystems also expose thenValue as an alias to emphasize the dependency on the previous value, while maintaining standard error propagation behavior.

Common features across implementations include support for chaining, predictable error handling, and preservation of the asynchronous context. Some libraries allow the transformation function to throw; in those cases, a failing transformation may convert exceptions into failed asynchronous results. Others require explicit error handling within thenValue.

Usage examples typically resemble: asyncResult.thenValue(x => x + 1), where the original value is transformed and delivered by the next stage of the pipeline. ThenValue is often discussed alongside related operators such as map, flatMap, and then, with the precise semantics depending on the language and library in use.