Function adt

adt<Name extends string, Spec extends Record<string, CaseSpec>>(
name: Name,
spec: Spec,
): Adt<Name, Spec>
Defines an algebraic data type. Each spec entry is either null (a nullary case, exposed as a frozen singleton value) or a function from constructor arguments to the case's fields.

Nothing is written to the global scope: all constructors live on the returned object.
Type Parameters
- Name extends string
- Spec extends Record<string, CaseSpec>
Parameters
- name: Name
- spec: Spec
Returns Adt<Name, Spec>
Example
```
const Shape = adt('Shape', {
  Circle: (radius: number) => ({ radius }),
  Rect: (w: number, h: number) => ({ w, h }),
});
type Shape = VariantOf<typeof Shape>;

const area = (s: Shape): number =>
  Shape.match(s, {
    Circle: ({ radius }) => Math.PI * radius ** 2,
    Rect: ({ w, h }) => w * h,
  });
```
- Defined in src/adt.ts:130