Special data types

Type	Description
`Callable`	A callable value that can be executed by passing arguments in parentheses in YQL SQL syntax or using the `Apply` function with the s-expressions syntax.
`Resource`	Resource is an opaque pointer to a resource you can pass between the user defined functions (UDF). The type of the returned and accepted resource is declared inside a function using a string label. When passing a resource, YQL checks for label matching to prevent passing of resources between incompatible functions. If the labels mismatch, a type error occurs.
`Tagged`	Tagged is the option to assign an application name to any other type.
`Generic`	The data type used for data types.
`Unit`	Unit is the data type used for non-enumerable entities (data sources and data sinks, atoms, etc.).
`Null`	Void is a singular data type with the only possible null value. It's the type of the `NULL` literal and can be converted to any `Optional` type.
`Void`	Void is a singular data type with the only possible `"null"` value.
`EmptyList`	A singular data type with the only possible [] value. It's the type of the `[]` literal and can be converted to any `List` type.
`EmptyDict`	A singular data type with the only possible `{}` value. It's a type of the `{}` literal and can be converted to any `Dict` or `Set` type.