Helper ChoiceTrap

Jan Burse, created Jun 19. 2019
package jekpro.model.builtin;
import jekpro.model.inter.AbstractChoice;
import jekpro.model.inter.Engine;
import jekpro.model.molec.AbstractUndo;
import jekpro.model.molec.CallFrame;
import jekpro.model.molec.EngineException;
import jekpro.model.molec.EngineMessage;
import jekpro.model.rope.Intermediate;
/**
* <p>Provides a choice point for catch/3.</p>
* <p/>
* Warranty & Liability
* To the extent permitted by applicable law and unless explicitly
* otherwise agreed upon, XLOG Technologies GmbH makes no warranties
* regarding the provided information. XLOG Technologies GmbH assumes
* no liability that any problems might be solved with the information
* provided by XLOG Technologies GmbH.
* <p/>
* Rights & License
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* and patent rights in particular - are the sole property of XLOG
* Technologies GmbH. If the company was not the originator of some
* excerpts, XLOG Technologies GmbH has at least obtained the right to
* reproduce, change and translate the information.
* <p/>
* Reproduction is restricted to the whole unaltered document. Reproduction
* of the information is only allowed for non-commercial uses. Selling,
* giving away or letting of the execution of the library is prohibited.
* The library can be distributed as part of your applications and libraries
* for execution provided this comment remains unchanged.
* <p/>
* Restrictions
* Only to be distributed with programs that add significant and primary
* functionality to the library. Not to be distributed with additional
* software intended to replace any components of the library.
* <p/>
* Trademarks
* Jekejeke is a registered trademark of XLOG Technologies GmbH.
*/
final class ChoiceTrap extends AbstractChoice {
private final int snap;
private final Intermediate goalskel;
private final AbstractUndo mark;
/**
* <p>Create a choice trap.</p>
*
* @param n The parent choice.
* @param c The engine snap.
* @param r The term list skeleton.
* @param u The term list display.
* @param m The engine mark.
*/
ChoiceTrap(AbstractChoice n, int c, Intermediate r,
CallFrame u, AbstractUndo m) {
super(n, u);
snap = c;
goalskel = r;
mark = m;
}
/**
* <p>Logically evaluate a term in a list of goals for an additional time.</p>
* <p>The result is returned via the contskel and contdisplay of the engine.</p>
*
* @param en The engine.
* @return True if the predicate succeeded, otherwise false.
* @throws EngineException Shit happens.
*/
public final boolean moniNext(Engine en)
throws EngineException, EngineMessage {
/* remove choice point */
en.choices = next;
en.number--;
try {
if (!en.runLoop2(snap, false))
return false;
en.contskel = goalskel;
en.contdisplay = goaldisplay;
en.fault = null;
} catch (EngineException x) {
en.contskel = goalskel;
en.contdisplay = goaldisplay;
en.fault = x;
en.cutChoices(snap);
en.releaseBind(mark);
} catch (EngineMessage y) {
EngineException x = new EngineException(y,
EngineException.fetchStack(en));
en.contskel = goalskel;
en.contdisplay = goaldisplay;
en.fault = x;
en.cutChoices(snap);
en.releaseBind(mark);
}
if (en.fault != null)
return SpecialControl.handleException(en);
if (en.number != snap) {
/* meta argument change */
next = en.choices;
/* reuse choice point */
en.choices = this;
en.number++;
}
return true;
}
/**
* <p>Free data used to logically evaluate a term an additional time.</p>
* <p>The current exception is passed via the engine fault.</p>
* <p>The new current exception is returned via the engine fault.</p>
* <p>The current contskel and contdisplay of the engine is not changed.</p>
*
* @param en The engine.
*/
public final void moniCut(Engine en) {
/* remove choice point */
en.choices = next;
en.number--;
/* backup continuation */
Intermediate r = en.contskel;
CallFrame u = en.contdisplay;
en.contskel = goalskel;
en.contdisplay = goaldisplay;
en.cutChoices(snap);
/* restore continuation */
en.contskel = r;
en.contdisplay = u;
}
}

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