Forest: A Language and Toolkit for Programming with Filestores

A filestore is a structured collection of data files housed in a conven-tional hierarchical file system. Many applications use filestores as a poor-man’s database, and the correct execution of these applica-tions requires that the collection of files, directories, and symbolic links stored on disk satisfy a variety of precise invariants. More-over, all of these structures must have acceptable ownership, per-mission, and timestamp attributes. Unfortunately, current program-ming languages do not provide support for documenting assump-tions about filestores, detecting errors in them, or safely loading from and storing to them. This paper describes the design, implementation, and semantics of Forest, a new domain-specific language for describing filestores. The language uses a type-based metaphor to specify the expected structure, attributes, and invariants of filestores. Forest generate