Clojure(Script) library for declarative data description and validation

 Schema is a rich language for describing data shapes, with a variety of
 features:
 .
  * Data validation, with descriptive error messages of failures (targeted at
    programmers)
  * Annotation of function arguments and return values, with optional runtime
    validation
  * Schema-driven data coercion, which can automatically, succinctly, and
    safely convert complex data types.