create memo ~dir bs is a store with predefined bindings bs. If a key is mentioned more than once in bs the last binding takes over. The store uses memo to determine other keys as needed. dir is a scratch directory used by key determination functions to write memoized file outputs.
dir s is the scratch directory of s. Key determination functions using this directory to write files should do so using nice file name prefixes (e.g. lowercased module or lib names) to avoid name clashes.