refine

DDataParser.checkerRefine(predicate, options?) creates a custom checker. It plugs in everywhere (schema.addChecker, checkers option, extended.refine API) and reuses the error engine (path, message, rejected value).

Interactive example

When to use it?

• Validate a business pattern not covered by native checkers (IBAN, slug, etc.).
• Centralize a reusable rule across multiple schemas (checkerRefine is a reusable value).
• Express rules on complex structures (objects, tuples...) by relying on addChecker.

Checker contract

The contract is based on the target parser output type: a checker DataParserChecker<..., T> is compatible with a parser whose output is T.

When the predicate is declared as a TypeScript type guard, the checker also refines the parser output type. This lets parse(...), Output<typeof schema>, Clean constraints, and NewTypes carry the validated subtype instead of the wider source type.

Type guard refinement

Additional examples

Validate coordinates

See also

• string - Parser for strings
• literal - Parser for literal values