src/builtin/PRED_$set_prolog_impl_flag_2.java

package com.googlecode.prolog_cafe.builtin;
import com.googlecode.prolog_cafe.lang.Operation;
import com.googlecode.prolog_cafe.lang.Predicate;
import com.googlecode.prolog_cafe.lang.Prolog;
import com.googlecode.prolog_cafe.lang.SymbolTerm;
import com.googlecode.prolog_cafe.lang.Term;
/**
   <code>'$set_prolog_impl_flag'/2</code><br>
   @author Mutsunori Banbara (banbara@kobe-u.ac.jp)
   @author Naoyuki Tamura (tamura@kobe-u.ac.jp)
   @version 1.0
*/
class PRED_$set_prolog_impl_flag_2 extends Predicate.P2 {
    private static final SymbolTerm DEBUG             = SymbolTerm.intern("debug");

    public PRED_$set_prolog_impl_flag_2(Term a1, Term a2, Operation cont) {
        arg1 = a1;
        arg2 = a2;
        this.cont = cont;
    }

    @Override
    public Operation exec(Prolog engine) {
        engine.setB0();
        Term a1, a2;
        a1 = arg1;
        a2 = arg2;
	a1 = a1.dereference();
	a2 = a2.dereference();

	if (a1.equals(DEBUG)) {
	    if (! (a2 instanceof SymbolTerm))
		return engine.fail();
	    engine.setDebug(((SymbolTerm)a2).name());
	} else {
	    return engine.fail();
	}
        return cont;
    }
}