?- json_object
      point(x:int, y:int, z:int=0).

The type arguments are either types as know to library(error) or functor names of other JSON objects. The constant any indicates an untyped argument. If this is a JSON term, it becomes subject to json_to_prolog/2. I.e., using the type list(any) causes the conversion to be executed on each element of the list.

If a field has a default, the default is used if the field is not specified in the JSON object. Extending the record type definition, types can be of the form (Type1|Type2). The type null means that the field may not be present.

Conversion of JSON to Prolog applies if all non-defaulted arguments can be found in the JSON object. If multiple rules match, the term with the highest arity gets preference.