VignetteEither

VignetteEither is a term used in programming documentation and teaching to describe a small, self-contained example that demonstrates how to work with an Either value. The concept combines the idea of a vignette—a brief, illustrative narrative or sample—with the Either data type, commonly used to represent a value that can be either a success (Right) or an error/failure (Left).

In languages that feature an Either type, such as Haskell, Scala, or TypeScript with a similar construct, a VignetteEither typically presents a concise scenario showing how an operation might yield a Left value, a Right value, or how those values are transformed or handled. The goal is to make behavior concrete: how errors propagate, how successes are processed, and how pattern matching or functional combinators like map and flatMap (or bind) affect the result.

Use cases for VignetteEither include documentation generation, educational tutorials, and example-driven testing. They help readers grasp error handling and flow control by providing readable, focused examples rather than abstract descriptions. While not a formal language feature, the vignette pattern is valued for clarity, reproducibility, and their ease of integration into API docs, learning materials, and lightweight demonstrations.

Examples typically show a Left case such as an invalid input error, a Right case with a valid value, and a brief demonstration of processing both cases. Variants may adapt the pattern to different languages’ idioms for Either-like types.

See also: Either type, Left, Right, pattern matching, functional error handling.