The Layers of Larceny’s Foreign Function Interface

The Foreign Function Interface (FFI) in Larceny supports interact-ing with dynamically loaded C libraries via glue code written in Scheme. The programmer does not need to develop any C code to interface with C libraries. The FFI is divided into layers of Larceny Scheme code; the lower layers implement kernel functionality, and the higher layers support portable glue code development. The lower level has two main features of interest. First, the FFI supports callbacks: objects that look like simple function pointers to foreign code but invoke Scheme closures when called. This re-quires generating specialized machine code, and is further compli-cated by the potential movement of the closures during garbage collections. Second, Larceny heaps can be dumped to disk and reloaded during a fresh runtime execution. The FFI automatically relinks the foreign procedures in such heaps. The higher level layers provide macros and procedures for ex-tracting information from header files and dictating how values translate between Scheme and foreign code. These tools ease devel-opment of portable glue code. The upper layers have simple imple-mentations and do not require much Larceny-specific functionality; they may be useful for the FFIs of other Scheme systems. 1