anchor.diff:  
     // Emit same type in-out increment operator.
     void emitPreOrPostOp(DartType tp) {
  -    if (tp == DartType.INT) {
  -      emit(oneOf(const <String>['++', '--']));
  -    } else {
  -      assert(false);
  -    }
  +    assert(tp == DartType.INT);
  +    emit(oneOf(const <String>['++', '--']));
     }
   
     // Emit one type in, boolean out operator.
  
positive.code:   }
  
    void emitChar() {
      switch (rand.nextInt(10)) {
        // Favors regular char.
        case 0:
          emit(oneOf(interestingChars));
          break;
        default:
          emit(regularChars[rand.nextInt(regularChars.length)]);
          break;
      }
    }
  
    void emitString({int length = 8}) {
      emit("'");
      for (int i = 0, n = rand.nextInt(length); i < n; i++) {
        emitChar();
      }
      emit("'");
  
negative.code:   bool emitThrow() {
      DartType tp = oneOfSet(dartType.allTypes);
      emitLn('throw ', newline: false);
      emitExpr(0, tp, includeSemicolon: true);
      return false;
    }
  
  