Ordered Types for Stream Processing of Tree-Structured Data

Suenaga et al. have developed a type-based framework for automatically translating tree-processing programs into streamprocessing ones. The key ingredient of the framework was the use of ordered linear types to guarantee that a treeprocessing program traverses an input tree just once in the depth-first, left-to-right order (so that the input tree can be read from a stream). Their translation, however, sometimes introduces redundant buffering of input data. This paper extends their framework by introducing ordered, non-linear types in addition to ordered linear types. The resulting transformation framework reduces the redundant buffering, generating more efficient stream-processing programs.