The extension package system allows the language compiled by Bigloo to be extended and this is achieved by associating an extension file with a suffix. The extension file is loaded at the beginning of a compilation and it can do three things: call extern programs (unix programs); define macros; modify the values of some of the compiler's variables (for example, the list of the libraries to be linked with). The Bigloo's initializing procedure is the following:

• If it exists, Bigloo loads the runtime-command file, see Section Compiler Description.
  
  
• It then parses the command line to find the source file to compile.
• It extracts the source file suffix and looks it up in its *auto-mode* variable.
• If the suffix is found, the associated file is loaded. This file could contain a function named *extend-entry* which must accept a list as argument. It is invoked with the Bigloo's unparsed arguments.
• The result of the *extend-entry* application has to be a regular list of arguments and these are parsed by Bigloo.

For now, two extension packages exist: the Meroon package which is a native version of the Christian Queinnec object language; the Camloo [SerranoWeis94] package which is a front end compiler for the Caml language [Caml-light]

Furthermore, Bigloo supports the -extend option which forces the usage of an extension file. When Bigloo encounters this option, it immediately loads the extension file, invoking the function *extend-entry* with the list of arguments which have not been parsed yet.

The extension files are always sought in the directory containing the Bigloo's libraries.