Going Against the Flow for Typeless Programming

We present YinYang, a language that supports typeless programming where all object types are inferred with full support for data polymorphic mutable fields, subtyping, genericity, overriding, and local reasoning about semantic feedback like type errors. YinYang supports these features by forgoing traditional set-based types, instead tracking usage requirements in modular term assignment graphs where necessary mixin-like trait extensions flow backward toward assignees to provide static feedback and a basis to form objects. The resulting programs lack type annotations but can still be separately compiled. This paper describes our design, trade-offs made for feasibility, and an implementation.