Abstract Alias Types for Recursive Data Structures

Linear type systems permit programmers to deallocate or explicitly recycle memory, but are severely restricted by the fact that they admit no aliasing. This paper describes a pseudo-linear type system that allows a degree of aliasing and memory reuse as well as the ability to de ne complex recursive data structures. Our type system can encode conventional linear data structures such as linear lists and trees as well as more sophisticated data structures including cyclic and doubly-linked lists and trees. In the latter cases, our type system is expressive enough to represent pointer aliasing and yet safely permit destructive operations such as object deallocation. We demonstrate the exibility ofour type system by encoding two common space-conscious algorithms: destination-passing style and Deutsch-Schorr-Waite or \link-reversal " traversal algorithms.