Type-based Optimization for Regular Patterns

Pattern matching mechanisms based on regular expressions feature in a number of recent languages for processing XML. The flexibility of these mechanisms demands novel approaches to the familiar problems of pattern-match compilation---how to minimize the number of tests performed during pattern matching while keeping the size of the output code small

Contractive Signatures with Recursive Types, Type Parameters, and Abstract Types

Although theories of equivalence or subtyping for recursive types have been extensively investigated, sophisticated interaction between recursive types and abstract types has gained little attention. The key idea behind type theories for recursive types is to use syntactic contractiveness, meaning every µ-bound variable occurs only under a type constructor such as → or ∗. This syntactic contractiveness guarantees the existence of the unique solution of recursive equations and thus has been considered necessary for designing a sound theory for recursive types. However, in an advanced type system, such as OCaml, with recursive types, type parameters, and abstract types, we cannot easily define the syntactic contractiveness of types. In this paper, we investigate a sound type system for recursive types, type parameters, and abstract types. In particular, we develop a new semantic notion of contractiveness for types and signatures using mixed induction and coinduction, and show that our type system is sound with respect to the standard call-by-value operational semantics, which eliminates signature sealings. Moreover we show that while non-contractive types in signatures lead to unsoundness of the type system, they may be allowed in modules. We have also formalized the whole system and its type soundness proof in Coq

Typed Iterators for XML

XML transformations are very sensitive to types: XML types describe the tags and attributes of XML elements as well as the number, kind, and order of their sub-elements. Therefore, operations, even simple ones, that modify these features may affect the types of documents. Operations on XML documents are performed by iterators that, to be useful, need to be typed by a kind of polymorphism that goes beyond what currently exists. For this reason these iterators are not programmed but, rather, hard-coded in the language. However, this approach soon reaches its limits, as the hard-coded iterators cannot cover fairly standard usage scenarios. As a solution to this problem we propose a generic language to define iterators for XML data to be grafted on some host programming language. We show that our language mostly offers the required degree of polymorphism, study its formal properties, and show its expressiveness and practical impact by providing several usage examples and encodings