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Elm Complete Course / Custom Types

Opaque module types

Learn Opaque module types in Elm with a construct-specific explanation, a unique example, a practical boundary, and a mastery check.

10 min read • Beginner

Opaque module 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 Opaque module 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

elm-03-10-opaque-module-types.elm
elm Try It Live 
module Account exposing (Account, create)

type Account = Account Int
create n = Account n
Edge case / engineering note

Pay attention to the contract exposed by the type, which members belong to instances versus the type itself, and what dispatch occurs at runtime.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

Opaque module types Mastery Check →
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