package tarau.jinni;
/**
  Symbolic constant, of arity 0.
*/

public class Const extends Nonvar {

  public final static Nil  aNil=new Nil();
  public final static Const aTrue=new true_();
  public final static Const aFail=new fail_();
  public final static Const  aYes=new Const("yes");
  public final static Const  aNo=new Const("no");
  public final static Const anEof=new Const("end_of_file");
  public final static Const the(Term X) {
     return (null==X)?Const.aNo:new Fun("the",X);
  }
    
  private String sym;

  public Const(String s) {
    sym=s.intern();   
  }

  public final String name() {
    return sym;
  }

  public String qname() {
    if(0==sym.length()) return "''";
    for(int i=0; i<sym.length(); i++) {
      if(!Character.isLowerCase(sym.charAt(i))) 
        return '\''+sym+'\'';
    }
    return sym;
  }
  
  public String toString() {
    return qname();
  }

  boolean bind_to(Term that,Trail trail) {
     return super.bind_to(that,trail) && ((Const)that).sym==sym;
  }

  public boolean eq(Term that) {
     return (that instanceof Const) && ((Const)that).sym==sym;
  }

  public String getKey() {
    return sym;
  }

  /**
    returns an arity normally defined as 0
    @see Term#CONST
  */
  public int getArity() {
    return Term.CONST;
  }

  /**
    creates a ConstBuiltin from a Const known to be registered as
    being a builtin while returning its argument unchanged if it
    is just a plain Prolog constant with no builtin code attached to it
  */
  Const toBuiltin() {
    if(name().equals(Const.aNil.name())) return Const.aNil;
    if(name().equals(Const.aNo.name())) return Const.aNo;
    if(name().equals(Const.aYes.name())) return Const.aYes;

    ConstBuiltin B=(ConstBuiltin)Init.builtinDict.newBuiltin(this);
    if(null==B) {
      //IO.mes("not a builtin:"+this);
      return this;
    }
    return B;
  }

  public String toUnquoted() {
    return name();
  }
}