Nulvariant

nulvariant is a term used in discussions of type systems to describe a discriminated union that explicitly includes a null case. It represents a data variant that can either carry a value of a given type or denote the absence of a value. The concept emphasizes that absence is a first-class variant, not merely a special value.

In a nulvariant, the type is a sum of several alternatives: Null (or None) and one or more value-bearing cases. This structure makes the possibility of missing data explicit in the type system and supports exhaustive pattern matching, allowing code to handle every alternative.

Origins and usage: The term is used in theoretical discussions and experimental language designs to compare with other optional types such as Option or Maybe. Proponents argue that nulvariants can reduce null-reference errors by forcing explicit handling of absence, while critics warn of added complexity and potential interop friction with libraries that use conventional nulls.

Example: In a hypothetical syntax, a nulvariant of a string might be declared as type StringNul = Null | Value(String). Pattern matching would then distinguish Null from Value(s).

Relation to related concepts: Nulvariant overlaps with discriminated unions and sum types, and it can be implemented in languages with explicit variant types. It is distinct from optional types purely modeled as Some/None, which often use a separate wrapper rather than a dedicated Null alternative.