import { arrayOf, isString, lazy, typedStruct } from 'is-kit';
import type { Predicate } from 'is-kit';

type Tree = {
  readonly value: string;
  readonly children: readonly Tree[];
};

const isTree: Predicate<Tree> = lazy(() =>
  typedStruct<Tree>()({
    value: isString,
    children: arrayOf(isTree),
  }),
);

isTree({
  value: 'root',
  children: [{ value: 'leaf', children: [] }],
}); // true

Initialization and caching

The factory runs on first use, and the returned predicate is cached after successful initialization. If the factory throws, the error is propagated and a later evaluation can retry initialization.

Circular input values

lazy makes recursive guard definitions possible. It does not detect cycles in the input value; validating cyclic data requires separate cycle handling.