Produce a hash for a type that is unique for that type. The hash takes both actual type names and type structure into account.
The purpose of the hash of a type is to be able to store the type of a persisted value together with the value. By comparing the type hash of a persisted value and the hash of expected type we can know if the persistened value is of the correct type.
The type hash uses a cryptographic hash and can only be used to test equality.
The type code preserves the exact structure of the type and can be used to check if one type is convertible to another in various ways.
Are the types strongly isomorphic, only allows change of type names.
read . show convert the first type to the second?
Allows changing type names,
allows permuting and/or adding constructors to the new type,
also allows permuting named fields of a constructor.
Can the generic JSON serializer and deserializer convert the first type to the second. Allows changing type names, allows permuting and/or adding constructors to the new type, also allows permuting and/or deleting named fields of a constructor. Furhermore, allows types with a single constructor to change constructor name.