Lazy

It’s possible to define a recursive schema using lazy evaluation. Unfortunately, due to a limitation of TypeScript, its type cannot be automatically inferred.

Example

import * as p from '@vbudovski/paseri';

type Node =
    | { type: 'file'; name: string }
    | { type: 'directory'; name: string; nodes: Node[] };

// Give TypeScript a hint about the recursive structure.
const schema: p.Schema<Node> = p.lazy(() =>
    p.union(
        p.object({
            type: p.literal('file'),
            name: p.string(),
        }),
        p.object({
            type: p.literal('directory'),
            name: p.string(),
            nodes: p.array(schema),
        }),
    ),
);
const data: Node = {
    type: 'directory',
    name: 'Documents',
    nodes: [
        {
            type: 'file',
            name: 'shopping_list.txt',
        },
        {
            type: 'directory',
            name: 'Pictures',
            nodes: [
                { type: 'file', name: 'cat.jpg' },
                { type: 'file', name: 'dog.jpg' },
            ],
        },
    ],
};

const result = schema.safeParse(data);
if (result.ok) {
    // result.value typed as `Node`.
}