event-level filtering

[c-dilks]

Algorithms should be able to filter out entire events, for example:

• QADB will need this
• InclusiveKinematics could use this for when no scattered lepton is found

Proposal:

• make Algorithm::Run return bool; a value of false will stop AlgorithmSequence::Run (which can also return false)
• handling action functions:
  • filter returns false(s)
  • transformers and creators need thought; ideas:
    • std::optional, but may not bind well
    • add a bool lvalue reference to all action functions
    • add a bool created member to creator-action-functions' return value structs

Example analysis, but with external event-level filters:

    /*****/
    iguana_InclusiveKinematics.Run(hipo_banks);
    // event filter: if no DIS electron found, skip event
    if(bank_inclusive_kin.getRowList().size() != 1) {
      iguana_InclusiveKinematics.GetLog()->Trace("event filtered out");
      continue;
    }
    /*****/
    iguana_SectorFinder.Run(hipo_banks);
    iguana_TrajLinker.Run(hipo_banks);
    iguana_CalorimeterLinker.Run(hipo_banks);
    iguana_FiducialFilter.Run(hipo_banks);
    // event filter: if Fiducial cuts filtered out DIS electron, skip event
    if(std::find(
          bank_particle.getRowList().begin(),
          bank_particle.getRowList().end(),
          bank_inclusive_kin.getShort("pindex", 0)
          ) == bank_particle.getRowList().end())
    {
      iguana_FiducialFilter.GetLog()->Trace("event filtered out");
      continue;
    }
    /*****/
    iguana_DihadronKinematics.Run(hipo_banks);
    // event filter: if no dihadrons found, skip event
    if(bank_dihadron_kin.getRowList().size() == 0) {
      iguana_DihadronKinematics.GetLog()->Trace("event filtered out");
      continue;
    }
    /*****/
    iguana_SingleHadronKinematics.Run(hipo_banks);
    // event filter: if no single hadrons found, skip event
    if(bank_single_hadron_kin.getRowList().size() == 0) {
      iguana_SingleHadronKinematics.GetLog()->Trace("event filtered out");
      continue;
    }
    /*****/