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Custom union types
Learn Custom union types in Elm with a construct-specific explanation, a unique example, a practical boundary, and a mastery check.
Custom union types is an atomic Elm topic inside Custom Types. The example below uses the actual construct named by the lesson rather than a generic placeholder.
Focus on what Custom union types changes: the input, binding, control path, object state, collection, runtime effect, or language contract. Then alter one value and verify that the behavior changes for a reason specific to this feature.
Topic-specific example
type Status = New | Paid | Sent
Pay attention to the contract exposed by the type, which members belong to instances versus the type itself, and what dispatch occurs at runtime.