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package hlt.language.design.types;
/**
* @version Last modified on Thu Mar 24 12:27:31 2016 by hak
* @author Hassan Aït-Kaci
* @copyright © by the author
*/
import hlt.language.tools.Misc;
import hlt.language.util.Locatable;
/**
* A Goal is anything that may be established and undone by a
* TypeChecker.
* Here are the different types of goals:
*
* - BaseTypeGoal,
*
- ArrayIndexTypeGoal,
*
- CheckExitableGoal,
*
- EmptyGoal,
*
- GlobalTypingGoal,
*
- PopExitableGoal,
*
- PruningGoal,
*
- PushExitableGoal,
*
- ResiduatedGoal,
*
- ShadowUnifyGoal,
*
- TypingGoal,
*
- UnifyBaseTypeGoal,
*
- UnifyGoal,
*
- NoVoidTypeGoal.
*
*/
abstract public class Goal extends TimeStamp
{
private boolean _isTrailable = true;
final void setIsTrailable (boolean isTrailable)
{
_isTrailable = isTrailable;
}
final void trail (TypeChecker typeChecker)
{
if (_isTrailable)
typeChecker.trail(this);
}
/**
* This method is called by the type checker to try and establish this goal.
*/
abstract void prove (TypeChecker typeChecker) throws StaticSemanticsErrorException;
/**
* This method is called by the type checker upon popping it from the goal trail.
* By default, it simply pushes this goal on the typechecker's goal stack.
*/
void undo (TypeChecker typeChecker)
{
typeChecker.pushGoal(this);
}
/**
* Returns this goal's location's extent as a
* Locatable.
*/
abstract Locatable extent ();
public String toString ()
{
return /* Misc.locationString(extent()) + */ "Goal " + timeStamp();
}
}