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LearnDataData definitions

Data definitions

Name variant data and record-shaped data.

data names a type-shaped value. It can describe a closed set of variants or a named record shape.

let Port := data {
  | Configured(port : Int, secure : Bool)
  | Default
};

let Settings := data {
  port : Int := 3000;
  label : String;
};

let Box[T] := data {
  value : T;
};

Define variants

Use | when each value is one case from a closed set.

let Port := data {
  | Configured(Int)
  | Default
};

let configured : Port := .Configured(8080);
let fallback : Port := .Default;

Use data definitions for states, events, parse results, and other values with a known list of cases.

Match variants

let value := match configured (
| .Configured(port) => port
| .Default => 3000
);

Each branch explains one shape. Keep branch bodies small. Move large work into named functions.

Define named records

Use fields without | when the type is one named record shape.

let Box[T] := data {
  value : T;
};

let boxedName : Box[String] := {
  value := "Nora"
};

boxedName.value;

The data definition names the record shape. The value still uses the normal record literal form, with := for each field value. Field access uses ..

Record-shaped data is useful when the field set is stable and the type name matters at module boundaries.

Named fields inside variants

A variant may carry named fields when the payload needs labels.

let Port := data {
  | Configured(port : Int, secure : Bool)
  | Default
};

let configured : Port := .Configured(secure := .True, port := 8080);

Named fields make construction order-independent. Do not mix positional and named field definitions inside one variant declaration.