Sharing analysis in the Pawns compiler

Abstract. Pawns is a programming language under development that supports algebraic data types, polymorphism, higher order functions and “pure ” declarative programming. It also supports impure imperative fea-tures including destructive update of shared data structures via pointers, allowing significantly increased efficiency for some operations. A novelty of Pawns is that all impure “effects ” must be made obvious in the source code and they can be safely encapsulated in pure functions in a way that is checked by the compiler. Execution of a pure function can per-form destructive updates on data structures that are local to or even-tually returned from the function without risking modification of the data structures passed to the function. This paper describes the shar-ing analysis which allows impurity to be encapsulated. Aspects of the analysis are similar to other published work, but in addition it handles explicit pointers and destructive update, higher order functions including closures and pre- and post-conditions concerning sharing for functions