/** Our internal representation of a IfZero expr
 * in the D0 language.
 * See http://www.radford.edu/itec380/2022fall-ibarland/Project
 * 
 * @author Ian Barland
 * @version 2023.Apr.10
 */
public record IfZero(Expr test, Expr thenAns, Expr elseAns) implements Expr {
  static final String START_TOKEN = "for";
  static final String CONT_TOKEN  = "gondor";
  
  
  public String toString() {
    return START_TOKEN + " "
         + this.test.toString() + " "
         + CONT_TOKEN + " "
         + this.thenAns.toString() + " "
         + this.elseAns.toString()
         ;
    }

  public static IfZero parse( java.util.Scanner s, String punctuation ) {
      UtilIan.verifyToken( UtilIan.nextSplittingBy(s,punctuation), START_TOKEN ); // consume&verify the "for"

      // NOTE: recur with `Expr.parse` -- not `parse` = `IfZero.parse` which is NOT what we want!
      Expr theTest       = Expr.parse(s,punctuation);
      UtilIan.verifyToken( UtilIan.nextSplittingBy(s,punctuation), CONT_TOKEN ); // consume&verify the "gondor"
      Expr theThenAnswer = Expr.parse(s,punctuation);
      Expr theElseAnswer = Expr.parse(s,punctuation);
      return new IfZero(theTest,theThenAnswer,theElseAnswer);
      }
    
    
  static final double EPSILON = 1e-10;
  public Value eval() {
    if ( Math.abs(((Num)(this.test.eval())).doubleValue()) < EPSILON ) {
      return this.thenAns.eval();
      }
   else {
      return this.elseAns.eval();
      }
    }
    
  }