import java.util.*;
aspect First {
  
  // *** API ***

  // A nonterminal has an attribute *first*
  // - the set of terminal symbols that derivations of the nonterminal can start with
  inh Set NDecl.first() circular [new HashSet()]; // The set of first symbols
  
  
  // *** Implementation ***
  
  syn Set Prod.first() circular [new HashSet()] {
    Set firstSet = new HashSet();
    if(getNumSymbol() == 0)
        return firstSet;
      firstSet.addAll(getSymbol(0).first());
      for(int i = 1; i < getNumSymbol() && getSymbol(i-1).nullable(); i++) {
        firstSet.addAll(getSymbol(i).first());
      }
    return firstSet;
  }
  
  syn Set Symbol.first() circular [new HashSet()] ;
  
  eq Terminal.first() {
    Set firstSet =  new HashSet();
    firstSet.add(id());
    return firstSet;
  }
  
  eq NUse.first() {
    return decl().first();
  }
  
  eq Rule.getNDecl().first() {
    Set firstSet = new HashSet();
    for (int i = 0; i < getNumProd(); i++) {
      firstSet.addAll(getProd(i).first());
    }
    return firstSet;
  }
}