Abstract:Package managers are legion. Every programming language and operating system has its own solution, each with subtly different semantics for dependency resolution. This fragmentation prevents multilingual projects from expressing precise dependencies across language ecosystems; it leaves external system and hardware dependencies implicit and unversioned; it obscures security vulnerabilities that lie in the full dependency graph. We present the \textit{Package Calculus}, a formalism for dependency resolution that unifies the core semantics of diverse package managers. Through a series of formal reductions, we show how this core is expressive enough to model the diversity that real-world package managers employ in their dependency expression languages. By using the Package Calculus as the intermediate representation of dependencies, we enable translation between distinct package managers and resolution across ecosystems.
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Project leaders had to find a way to "compensate" for killing thousands of fish every year. Plans were drawn up to flood 900 acres of farmland in Gloucestershire, on the banks of the Severn, to create saltmarsh habitats for breeding fish.
面向未来，习近平总书记对长江经济带发展提出要求：应该在践行新发展理念、构建新发展格局、推动高质量发展中发挥重要作用。