2 A small Example

#include "mozart.h"                                  // 1
                                                     // 2
OZ_BI_define(BIgetenv,1,1)                           // 3
{                                                    // 4
  OZ_declareAtom(0,envVarName);                      // 5
                                                     // 6
  char *envValue = getenv(envVarName);               // 7
                                                     // 8
  if (envValue == 0) /* not defined in environment */// 9
    return OZ_FAILED;                                //10
                                                     //11
  OZ_RETURN_ATOM(envValue);                          //12
} OZ_BI_end                                          //13
                                                     //14
                                                     //15
static OZ_C_proc_interface oz_interface[] = {        //16
  {"getenv",1,1,BIgetenv},                           //17
  {0,0,0,0}                                          //18
};                                                   //19
                                                     //20
OZ_C_proc_interface *oz_init_module() {              //21
  return oz_interface;                               //22
}                                                    //23

Suppose we want to provide an Oz native module Goodies containing a single procedure {Goodies.getenv VarA ValueA} as an interface to the C library function getenv(3): it constrains ValueA to an atom, which is the value of the environment variable VarA, where VarA is an atom. Thus {Goodies.getenv 'HOME' X} will constrain X to an atom representing the path to our home directory. To realize this we have to perform the following steps:

1. Write a piece of C code.

2. Create an object file from the C code.

3. Create a dynamic library from the object file(s).

4. Link the library into Oz.

These steps are explained in more detail below.