Ftypes: Structured foreign types Andrew W. Keep R. Kent Dybvig Indiana University fakeep,
[email protected] Abstract When accessing scalar elements within an ftype, the value of the High-level programming languages, like Scheme, typically repre- scalar is automatically marshaled into the equivalent Scheme rep- sent data in ways that differ from the host platform to support resentation. When setting scalar elements, the Scheme value is consistent behavior across platforms and automatic storage man- checked to ensure compatibility with the specified foreign type, and agement, i.e., garbage collection. While crucial to the program- then marshaled into the equivalent foreign representation. Ftypes ming model, differences in data representation can complicate in- are well integrated into the system, with compiler support for ef- teraction with foreign programs and libraries that employ machine- ficient access to foreign data and debugger support for convenient dependent data structures that do not readily support garbage col- inspection of foreign data. lection. To bridge this gap, many high-level languages feature for- The ftype syntax is convenient and flexible. While it is similar in eign function interfaces that include some ability to interact with some ways to foreign data declarations in other Scheme implemen- foreign data, though they often do not provide complete control tations, and language design is largely a matter of taste, we believe over the structure of foreign data, are not always fully integrated our syntax is cleaner and more intuitive than most. Our system also into the language and run-time system, and are often not as effi- has a more complete set of features, covering all C data types along cient as possible.