TouchCost: Cost Analysis of TouchDevelop Scripts

TouchDevelop is a novel programming environment and language for mobile devices. TouchDevelop applications are typically developed by non-expert users, rather small, and published on the cloud. In this paper, we introduce TouchCost, a new static analysis that infers the cost of loops in TouchDevelop programs. TouchCost (i) applies an existing generic analyzer to infer numerical invariants, (ii) extracts cost relation systems from these invariants, and (iii) solves them using an existing upper bound solver. TouchCost has been implemented and applied to all TouchDevelop scripts that are currently published on the cloud. Experimental results show that TouchCost is both scalable and precise. Studying the outputs of TouchCost, we glimpse two major applications: (i) establishing at runtime the cost of a loop, and move its execution to the cloud if it is too expensive w.r.t. the available resources, and (ii) helping a non-expert developer to debug his program.