IsoLATE: A Type System for Self-recursion

  • Ravi ChughEmail author
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9032)


A fundamental aspect of object-oriented languages is how recursive functions are defined. One semantic approach is to use simple record types and explicit recursion (i.e. fix) to define mutually recursive units of functionality. Another approach is to use records and recursive types to describe recursion through a “self” parameter. Many systems rely on both semantic approaches as well as combinations of universally quantified types, existentially quantified types, and mixin operators to encode patterns of method reuse, data encapsulation, and “open recursion” through self. These more complex mechanisms are needed to support many important use cases, but they often lack desirable theoretical properties, such as decidability, and can be difficult to implement, because of the equirecursive interpretation that identifies mu-types with their unfoldings. Furthermore, these systems do not apply to languages without explicit recursion (such as JavaScript, Python, and Ruby). In this paper, we present a statically typed calculus of functional objects called ISOLATE that can reason about a pattern of mixin composition without relying on an explicit fixpoint operation. To accomplish this, ISOLATE extends a standard isorecursive type system with a mechanism for checking the “mutual consistency” of a collection of functions, that is, that all of the assumptions about self are implied by the collection itself. We prove the soundness of ISOLATE via a type-preserving translation to a calculus with F-bounded polymorphism. Therefore, ISOLATE can be regarded as a stylized subset of the more expressive calculus that admits an interesting class of programs yet is easy to implement. In the future, we plan to investigate how other, more complicated forms of mixin composition (again, without explicit recursion) may be supported by lightweight type systems.


Type System Operational Semantic Recursive Function Recursive Call Open Recursion 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.University of ChicagoChicagoUSA

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