Building standalone applications

A standalone application is a program that can be executed without the need to start the B-Prolog interpreter first. You do not have to use the external language interface to build standalone applications. The default initial predicate that the B-Prolog interpreter executes is called main/0. In version 6.9 and later, an initial goal can be given as a command line argument -g Goal. For example, the following command

      bp myprog.out -g ``mymain(Output),writeln(Output)''

loads the binary file myprog.out and executes the goal

      mymain(Output),writeln(Output)

instead of the default initial goal main.

You can also build a Prolog program as a standalone application by re-defining the main/0 predicate. The following definition is recommended:

      main:-
          get_main_args(L),
          call_your_program(L).

where get_main_args(L) fetches the command line arguments as a list of atoms, and call_your_program(L) starts your program. If the program does not need the command line arguments, then the call get_main_args(L) can be omitted.

The second thing you need to do is to compile the program and let your main/0 predicate overwrite the existing one in the system. Assume the compiled program is named myprog.out. To let the system execute main/0 in myprog.out instead of the one in the system, you need to either add myprog.out into the command line in the shell script bp (bp.bat for Windows) or start the system with myprog.out as an argument of the command line as in the following:

      bp myprog.out

For example, assume call_your_program(L) only prints out L, then the command

      bp myprog.out a b c

gives the following output:

      [a,b,c]