enhancement: use more specific type for action result term

alpha-core/src/main/java/at/ac/tuwien/kr/alpha/core/actions/ActionExecutionServiceImpl.java

@@ -1,14 +1,14 @@
 package at.ac.tuwien.kr.alpha.core.actions;
 
+import at.ac.tuwien.kr.alpha.api.grounder.Substitution;
+import at.ac.tuwien.kr.alpha.api.programs.actions.Action;
+import at.ac.tuwien.kr.alpha.api.programs.terms.ActionResultTerm;
+import at.ac.tuwien.kr.alpha.api.programs.terms.Term;
+
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
-import at.ac.tuwien.kr.alpha.api.programs.terms.Term;
-import at.ac.tuwien.kr.alpha.api.programs.terms.FunctionTerm;
-import at.ac.tuwien.kr.alpha.api.grounder.Substitution;
-import at.ac.tuwien.kr.alpha.api.programs.actions.Action;
-
 public class ActionExecutionServiceImpl implements ActionExecutionService {
 
 	private final ActionImplementationProvider actionProvider;
@@ -18,6 +18,8 @@ public ActionExecutionServiceImpl(ActionImplementationProvider implementationPro
 		this.actionProvider = implementationProvider;
 	}
 
+	// TODO possible bug: For two identical rules, the action should only be executed once - test this.
+	//  Note that there may be more answers to this: Formally, a program is a *set* of rules, i.e. duplicate rules are not allowed.
 	@Override
 	public ActionWitness execute(String actionName, int sourceRuleId, Substitution sourceRuleInstance, List<Term> inputTerms) {
 		ActionInput actInput = new ActionInput(actionName, sourceRuleId, sourceRuleInstance, inputTerms);
@@ -26,7 +28,7 @@ public ActionWitness execute(String actionName, int sourceRuleId, Substitution s
 
 	private ActionWitness execute(ActionInput input) {
 		Action action = actionProvider.getSupportedActions().get(input.name);
-		FunctionTerm result = action.execute(input.inputTerms);
+		ActionResultTerm<?> result = action.execute(input.inputTerms);
 		return new ActionWitness(input.sourceRule, input.instance, input.name, input.inputTerms, result);
 	}