@Override
  public Result calculateResult(Expression @NotNull [] params, final ExpressionContext context) {
    if (params.length != 0) return null;

    final Project project = context.getProject();
    final int offset = context.getStartOffset();

    PsiFile file = PsiDocumentManager.getInstance(project).getPsiFile(context.getEditor().getDocument());
    PsiElement place = file.findElementAt(offset);
    PsiVariable[] vars = MacroUtil.getVariablesVisibleAt(place, "");
  ChooseLetterLoop:
    for(char letter = 'i'; letter <= 'z'; letter++){
      for (PsiVariable var : vars) {
        PsiIdentifier identifier = var.getNameIdentifier();
        if (identifier == null || place.equals(identifier)) continue;
        if (var instanceof PsiLocalVariable) {
          PsiElement parent = var.getParent();
          if (parent instanceof PsiDeclarationStatement) {
            if (PsiTreeUtil.isAncestor(parent, place, false) &&
                var.getTextRange().getStartOffset() > place.getTextRange().getStartOffset()) {
              continue;
            }
          }
        }
        String name = identifier.getText();
        if (name.length() == 1 && name.charAt(0) == letter) {
          continue ChooseLetterLoop;
        }
      }
      return new TextResult(String.valueOf(letter));
    }

    return null;
  }
@Override
  public Result calculateResult(Expression @NotNull [] params, final ExpressionContext context)