Flow Typing, A New Lens on Linearity

Linear type systems enforce that each value is used exactly once, which can prevent common programming errors such as forgetting to close resources. Traditional solutions to the threading problem of using values multiple times often require adding extra language features, which can complicate the core language and its semantics.

Flow typing is a new approach that utilizes lenses, a functional representation of mutable references, to address this issue without extending the core language. Lenses allow for controlled mutation of specific parts of a stateful typing context. By being purely functional, flow typing can be implemented within a standard linear lambda calculus, resulting in a straightforward and direct semantics.