Effects for Funargs

Stack allocation and first-class functions don’t naturally mix together. In this paper we show that a type and effect system can be the detergent that helps these features form a nice emulsion. Our interest in this problem comes from our work on the Chapel language, but this problem is also relevant to lambda expressions in C++ and blocks in Objective C. The difficulty in mixing first-class functions and stack allocation is a tension between safety, efficiency, and simplicity. To preserve safety, one must worry about functions outliving the variables they reference: the classic upward funarg problem. There are systems which regain safety but lose programmerpredictable efficiency, and ones that provide both safety and efficiency, but give up simplicity by exposing regions to the programmer. In this paper we present a simple design that combines a type and effect system, for safety, with function-local storage, for control over efficiency.