Project : cristal

Section: Scientific Foundations

The Caml programming language

Caml belongs to the ML family of languages. Like all languages of this family, Caml supports both functional and imperative programming styles, Hindley-Milner static typing with type inference, and features a powerful module system. Caml also supports class-based object-oriented programming, and has an efficient compiler.

Initially built around a functional kernel with imperative extensions, the ML language evolved in two independent ways during the 80's. First, a group headed by Robin Milner designed Standard ML (SML), whose most innovative feature was its module system, designed by David MacQueen. In parallel, Caml was first designed and developed in the Formel group at INRIA, in collaboration with members of the C.S. Lab. of École Normale Supérieure in Paris, and then in the Cristal group. Xavier Leroy designed and implemented a module system similar to that of SML, but with a greater focus on separate compilation. Didier Rémy and Jérôme Vouillon built the object layer. The version of Caml including these features is called Objective Caml (OCaml).

From an implementation point of view, Caml has advanced the state of the art in compiling functional languages. Initially based on the Categorical Abstract Machine, which was implemented on top of a Lisp runtime system, Caml's execution model was first changed to a high-performance bytecoded virtual machine designed by Xavier Leroy and complemented by Damien Doligez's generational and incremental garbage collector [48]. The resulting implementation, Caml-Light, has low memory requirements and high portability, which made it quite popular for education.

Then, on the way from Caml-Light to Objective Caml, Xavier Leroy complemented the bytecode generator with a high-performance native code compiler featuring optimizations based on control-flow analyses, good register allocation, and code generators for 9 different processors. The combination of the two compilers provides portability and short development cycle, thanks to the bytecode compiler, as well as excellent performance, thanks to the native code generator.