3.7.1.1 Library declaration

A library declaration contains the following elements:

• The ?library-name specifies the name of the library (possibly with version).
• The export subform specifies a list of exports, which names a subset of the bindings defined within or imported into the library.
• The import subform specifies the imported bindings as a list of import dependencies, where each dependency specifies:
  • - The imported library’s name, and, optionally, constraints on its version.
  • - The relevant levels, e.g. expand or run time.
  • - The subset of the library’s exports to make available within the importing library, and the local names to use within the importing library for each of the library’s exports.
• The ?library-body is the library body, consisting of a sequence of definitions followed by a sequence of expressions. The definitions may be both for local (unexported) and exported bindings, and the expressions are initialization expressions to be evaluated for their effects.

An identifier can be imported with the same local name from two or more libraries or for two levels from the same library only if the binding exported by each library is the same (i.e., the binding is defined in one library, and it arrives through the imports only by exporting and re–exporting). Otherwise, no identifier can be imported multiple times, defined multiple times, or both defined and imported. No identifiers are visible within a library except for those explicitly imported into the library or defined within the library.