We propose a new configuration language, component and service library, and compiler that make it easier to develop efficient sensor network applications. Our 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. Our language, library, and compiler are collectively called SNACK (Sensor Network Application Construction Kit). We describe them, and present and evaluate a simple SNACK-based multihop data collection application. This application uses SNACK language features to provide both simplicity (excluding reusable service definitions, its description is three lines long) and efficiency (it performs comparably to the well-kn...