CS790 MEng Project
 
Multithreaded ML Interpreter
 
Suwat Ch.
 
 
 

What is Caml ?

Contact the author Pierre.Weis@inria.fr
Original Page can be found at INRIA homepage

Created in January 1996.

Caml is a programming language, easy to learn, easy to use, and yet amazingly powerful.

It is developped and distributed by INRIA (the main french research institute for computer science), since 1984. It is freely available for Unix, PC or Macintosh.

There exist two flavors of Caml: Caml Light and Objective Caml. Caml Light is merely a subset of Objective Caml, especially designed for teaching and learning the art of programming.
In addition to the Caml Light's core language, Objective Caml features a powerful modules system, full support to object-oriented paradigm, and an optimizing compiler.

I give here a short overview of the language, that let you get an idea of the salient features of Caml.

Availability

Caml is freely available, and highly portable, since it runs under virtually any Unix, PC, or Macintosh platform. To get the CD-ROM, mail to
INRIA-Diffusion
Distribution de Caml Light
B.P. 105
78153 Le Chesnay CEDEX
FRANCE

send an envelope (that can contain a CD-ROM), with your name and adress.

Safety

Caml is a safe language. The compiler performs many sanity checks on programs before compilation. That's why many programming errors cannot happen in Caml: data type confusions, erroneous accesses into compound values become just impossible. In effect, all these points are carefully verified by the compiler, so that they data accesses can be delagated to the compiler code generator, to ensure that data manipulated by programs may never be corrupted: the perfect integrity of data manipulated by programs is granted for free in Caml.

Caml is statically type-checked, but there is no need to add type informations in programs (as in Ada or Pascal, or C): type annotations are fully automatic and handled by the compiler.

Data Types

Numerous data types are predefined in Caml. This includes: Beyond these powerful predefined types, Caml offers powerful means to defined new data types: records, enumerated types, and sum types. Sum types can be thought as a generalization of union data types, that is clean, powerful, and yet simple to understand. They allow unrestricted definitions of heterogeneous values, tagged by data constructors.

As desired, these types can be defined concretely (data constructors are available from outside the module) or abstractly (this implémentation is restreinted to the defining module, and the data constructors are not accessible from outside the module).

This mechanism provides a fine tuning over data encapsulation, which is mandatory for programming in the large.

Functions

Caml is a functional programming language: there is no restrictions in the definition and usage of functions, that can be passed as arguments or returned as values.

Automatic memory management and incremental garbage collection

Caml features automatic memory management: allocation and deallocation of data structures is kept implicit (there is no ``new'' or ``free'' primitives), and handled by the compiler. This way programs are much safer, since spurious memory corruptions can never occur.
Moreover the memory manager works in parallel with the application, so that there is no noticeable stop of the Caml program when the garbage collector is running.

Imperative features

Caml provides full imperative capabilities, including updatable arrays, imperative variables and records with mutable fields.

Modules

Caml provides batch compilation, and separate compilation is obtained via the module system. The Caml Light compiler generates executable programs that are both small and portable.

Interactivity

Caml provides an interactive toplevel ``read-eval-print'' loop, that is convenient for both learning and debugging: no need to use files, nor add printing routines to get results.

Symbolic capabilities

Caml features pattern matching: it provides a concise, simple, and elegant ``test and bind'' facility for symbolic computation.

Error recovery

Caml has a general exception mechanism to handle or recover from errors or exceptional situations.

Polymorphism

Caml features ``polymorphic typing'': some types may be left unspecified, standing for ``any type''. That way, functions and procedures that are general purpose may be applied to any kind of data, regardless of their types (e.g. sorting routines may be applied to any kind of arrays).

Evaluation regime

Caml is a strict language, as opposed to lazy ones. However, first-order value functions allows the manipulation of delayed expressions, and thus lazy evaluation of potentially infinite data structures is still possible.

Powerful libraries

There are a lot of libraries and contributions available in Caml, including portable graphics (libgraph), a package of multi-precision arithmetics (rational numbers), and various interfaces with well-known technology: lexer and parser generators with camllex and camlyacc. Under Unix, you also get a debugger, a Caml source browser (camlbrowser), a user graphical interface using Tk/Tcl with camltk, and an interface with the operating system (libunix).
 

 

Caml and education

Caml is used in education to teach programming courses, from beginners to graduate students. In this area, the automatic memory management and the type system are of prime utility.
Courses in the large for beginners are: CNAM (10000 students), option informatique des classes préparatoires aux grandes Écoles (1000 students ).
Among courses for advanced students let me cite: École Polytechnique (100 students), and École Normale Supérieure (50 students).

Caml and applications

Caml is used to implement complex systems such as theorem provers or compilers. A good compiler written in Caml is Caml Light! The coq theorem prover is written in Caml. Ensemble, a toolkit for building distributed applications developed at Cornell University is written in Objective Caml. The web browser MMM is also written in Caml.

 

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