Minimal Schemable Example

schemable.ts

/*******************************************************************************
 * Kinds Type
 * @description A registry for Kind URIS with their substitution strategies.
 * Note that the idiomatic replacement type for kinds uses _0 as the inner-
 * most hole for Functor and Chain. Thus Either<L, R> should use the hole
 * order of Either<_1, _0>. This is reflected in the replacement strategies
 * used in type_classes.ts
 ******************************************************************************/

export interface Kinds<A, B, C, D> {
  ["Test"]: Test<A>;
}

/*******************************************************************************
  * URIS Type
  * @description A union of all visible Kinds
  ******************************************************************************/

export type URIS = keyof Kinds<any, any, any, any>;

/*******************************************************************************
  * Kind Type
  * @description A lookup type used to specify a Kind substitution
  ******************************************************************************/

export type Kind<URI extends URIS, A, B, C, D> = Kinds<A, B, C, D>[URI];

// Test

export type StructSchemable<URI extends URIS> = {
  readonly struct: <A, B = never, C = never, D = never>(
    properties: { [K in keyof A]: Kind<URI, A[K], B, C, D> },
  ) => Kind<URI, { [K in keyof A]: A[K] }, B, C, D>;
};

export type Schemable<URI extends URIS> = StructSchemable<URI>;

type Test<A> = (r: unknown) => A;

type TypeOf<T> = T extends Test<infer A> ? A : never;

const { struct }: StructSchemable<"Test"> = {
  struct: (properties) =>
    (i) => {
      let out: Record<string, unknown> = {};
      for (const key in properties) {
        const t = properties[key];
        const o = t(i);
        out[key] = o;
      }
      return out as {
        [K in keyof typeof properties]: TypeOf<(typeof properties)[K]>;
      };
    },
};

const number: Test<number> = (i: unknown): number => 1;

const a1 = struct({ one: number });