OCaml

Objective Caml, also known as OCaml or O'Caml for short, is an advanced programming language that is part of the ML family. It is developed and distributed as Open-source by INRIA. Ocaml was created in 1996 as a successor to Caml Light. Its authors include Xavier Leroy, Jerome Vouillon and Damien Doligez.

CAML originally stood for Categorical Abstract Machine Language. OCaml has not been based on this abstract machine for a long time.

OCaml shares the functional and imperative features of ML, but contains object-oriented concepts and some minor syntax differences.

Features

Performance distinguishes OCaml from other languages in the ML family. The runtime system was designed to be fast, efficient, and rather frugal in memory. Ocaml provides a bytecode compiler, a script interpreter or toplevel evaluation loop, and an optimizing native code compiler. The code generated by the native code compiler is typically comparable to C/C++ in efficiency. See for instance The Computer Language Shootout Benchmarks.

Powerful features of the language include a static type system, type inference, parametric polymorphism, tail recursion, pattern matching, first class lexical closures, functors (parametric modules), exception handling, and incremental generational automatic garbage collection. It also has a quite concise syntax. The object system provides for multiple inheritance, object construction directly (by specifying methods for a unique object) or from classes, and structural subtyping (objects are of compatible types if their methods are compatible, regardless of what was inherited from what).

OCaml features are pragmatically balanced between expressivity and new features on the one side and ease of interfacing with existing systems and libraries and efficiency on the other side. Ocaml contains support for familiar functions such as printf, and a foreign function interface which permits easy linking with C primitives, including language support for efficient numerical arrays in formats compatible with both C and FORTRAN.

The OCaml distribution includes a powerful preprocessor (which permits syntactical extensions), a debugger (which includes the ability to step backwards in time when investigating an error), a documentation generator, a profiler, and numerous general purpose libraries. The compiler is available for a range of platforms, including Unix, Windows, and Macintosh, with native code generation for all major architectures (IA32, PowerPC, AMD64, Sparc, IA64, Alpha, HP/PA, MIPS, StrongARM), thus providing good portability.

Uses

OCaml is used in a wide range of applications, including theorem proving and computer program analysis. It is also used in applications such as MLDonkey (a popular P2P program supporting multiple networks) and the Unison File Synchronizer.

Programs implemented in Ocaml have won prizes several times in the ICFP programming contest.

Ocaml is used as an introductory language in many universities, including École Normale Supérieure, Institut d'Informatique d'Entreprise, EPITA, Caltech, Brown University, and the University of Pisa. It is also used to teach Computer Science (mainly Algorithms and Complexity theories) in the French Classes Préparatoires (Preparation Courses), for students who choose to study Computer Science (and has almost replaced Pascal for that).

See also

• Standard ML
• F Sharp, an OCaml-like compiler for Microsoft .NET
• EML, a different kind of object-oriented extension to ML
• O'Haskell an object-oriented extension to Haskell, a functional language different from ML

External links

• Caml language family official website
• OCaml libraries
• OCaml tutorial for C, C++, Java and Perl programmers
• A book on OCaml in the context of scientific programming
• Comparison of the speed of various languages (with favorable results for Ocaml)
• Unison File Synchronizer
• Developing applications with Objective CAML
• LablGL (OpenGL+ interface)
• LablGTK (GTK+ interface)

Code examples

Hello World

  print_endline "Hello world!";;

Birthday Paradox

The following is an OCaml script which calculates the number of people who need to be in a room before the probability of two sharing the same birthday becomes larger than 50% (the so-called birthday paradox).

It also demonstrates OCaml's use as a scripting language. On a unix-like machine, save this to a file, chmod it to be executable (chmod 0755 birthday.ml) and run it directly from the command line (./birthday.ml).

#!/usr/bin/ocamlrun /usr/bin/ocaml

let size = 365. ;;

let rec loop p i =
  let p' = (size -. (float (i-1))) *. p /. size in
  if p' < 0.5 then
    Printf.printf "answer = %d\n" i
  else
    loop p' (i+1) ;;
loop 1.0 2