Uniqueness Typing in Theory and Practice

We present uniqueness typing as an extension of a familiar Curry style typing system for graph rewrite systems. This provides a method for combining purely functional programming with operations having side-eeects, while preserving the functional nature of the language. We give a technical account as well as the underlying intuition. The system is shown to be eeective in the sense that a uniqueness variant of a given conventional type can be determined automatically. Finally, this paper gives some examples of the application of uniqueness typing in the programming language Clean.