The Sensor Network Application Construction Kit (SNACK) provides a new configuration language, component and service library, and compiler that make it easier to develop efficient sensor network applications. The goal is the construction of smart application service libraries: high-level libraries that implement concepts like routing trees and periodic sensing, and that combine automatically into efficient programs. Important language features include flexible control over component sharing and transitive arrow connections, which let independently-implemented services knit themselves into integrated control flow paths.