Polymorphic lambda calculus with context-free session types

Session types provide a typing discipline for structured communication on bidirectional channels. Context-free session overcome the restriction to tail recursive protocols characteristic of conventional types. This extension enables serialization and deserialization tree structures in fully type-safe manner. We present theory underlying language FreeST 2, which features context-free an System F with linear kinding system distinguish message types, channel The presents metatheoretical challenges we address: contractivity presence polymorphism, non-trivial equational decidability type equivalence. also establish standard results preservation, progress, characterization erroneous processes.