Calling Prolog from Java

A Prolog call is an instance of the class bprolog.plc.Plc. It is convenient to import the class first:

      import bprolog.plc.Plc;

The class Plc contains the following constructor and methods:

• public Plc(String functor, Object args[]): This is a constructor that constructs a Prolog call, where functor is the predicate name, and args is the sequence of arguments of the call. If a call does not carry any argument, then just give the second argument an empty array, new Object[] {}.

• public static void startPlc(String args[]): Initializes the B-Prolog emulator, where args are parameter-value pairs that are given to B-Prolog. Possible parameter-value pairs include:

  "-b" TRAIL	words that are allocated to the trail stack
  "-s" STACK	words that are allocated to the local and to the heap
  "-p" PAREA	words that are allocated to the program code area
  "-t" TABLE	words that are allocated to the table area

  TRAIL, STACK, PAREA, and TABLE must all be strings of integers. After the B-Prolog emulator is initialized, it will be waiting for calls from Java. Initialization only needs to be done once. Further calls to startPlc do not have any effect.

• public static native boolean exec(String command): Executes a Prolog call, as represented by the string command. This method is static, and, thus, can be executed without creating any Plc object. In order to call a predicate in a file, say xxx.pl, it is first necessary to have the Prolog program loaded into the system. In order to do so, just execute the method exec("load(xxx)") or exec("consult(xxx)").

• public boolean call(): Executes the Prolog call, as represented by the Plc object that owns this method. The return value is true if the Prolog call succeeds, and the return value is false if the call fails.