How to cache function Boolean result

Question

I have this function:

var
  _WordApplicationExistsCache: Integer = -1; // Cache result

function WordApplicationExists: Boolean;
var
  WordObj: OleVariant;
begin
  if (_WordApplicationExistsCache = -1) then
  begin
    Result := False;
    try
      try
        WordObj := CreateOleObject('Word.Application');
        WordObj.Visible := False;
        WordObj.Quit;
        WordObj := Unassigned;
        Result := True;
      except
        // error
      end;
    finally
      _WordApplicationExistsCache := Ord(Result); // 0;1
    end;
  end
  else
  begin
    Result := Boolean(_WordApplicationExistsCache);
  end;
end;

I'm trying to call this function only once in the Application lifetime. I might not call this function at all.

Is this the correct pattern? Can this be done better?

EDIT: Another way I can think of, in this case is to use 2 variables:

var
  _WordApplicationExistsInitialized: Boolean = False; // Cache result
  _WordApplicationExistsCacheResult: Boolean; // Undefined ?

function WordApplicationExists: Boolean;
var
  WordObj: OleVariant;
begin
  if not _WordApplicationExistsInitialized then
  begin
    _WordApplicationExistsInitialized := True;
    Result := False;
    try
      try
        WordObj := CreateOleObject('Word.Application');
        WordObj.Visible := False;
        WordObj.Quit;
        WordObj := Unassigned;
        Result := True;
      except
        // error
      end;
    finally
      _WordApplicationExistsCacheResult := Result;
    end;
  end
  else
  begin
    Result := _WordApplicationExistsCacheResult;
  end;
end;

What bugs me a bit about the first version is the type casting Boolean<->Integer. If Boolean could be initialized to nil it would have been perfect (I think).

Answer 1

Use a TriState type for the cached result.

type
  TTriState = ( tsUnknown, tsFalse, tsTrue );

var
  _WordApplicationExists : TTriState = tsUnknown;

function WordApplicationExists : Boolean;
var
  WordObj: OleVariant;
begin
  if _WordApplicationExists = tsUnknown 
  then
    try
      WordObj := CreateOleObject('Word.Application');
      WordObj.Visible := False;
      WordObj.Quit;
      WordObj := Unassigned;
      _WordApplicationExists := tsTrue;
    except
      _WordApplicationExists := tsFalse;
    end;

  Result := _WordApplicationExists = tsTrue;
end;