Complexity of Fractran and Productivity

Abstract. In functional programming languages the use of infinite structures is common practice. For total correctness of programs dealing with infinite structures one must guarantee that every finite part of the result can be evaluated in finitely many steps. This is known as productivity. For programming with infinite structures, productivity is what termination in well-defined results is for programming with finite structures. Fractran is a simple Turing-complete programming language invented by Conway. We prove that the question whether a Fractran program halts on all positive integers is 0 2-complete. In functional programming, productivity typically is a property of individual terms with respect to the inbuilt evaluation strategy. By encoding Fractran programs as specifications of infinite lists, we establish that this notion of productivity is 0 2-complete even for some of the most simple specifications. Therefore it is harder than termination of individual terms. In addition, w...

• Type: Conference
• Year: 2009
• Where: CADE
• Authors: Clemens Grabmayer, Dimitri Hendriks, Jörg Endrullis
• Keywords: Automated Reasoning, CADE 2009, Functional Programming, Infinite Structures, Simple Turing-complete Programming