How to grant permissions on a table-valued function Am I doing it right...?

I have a function that returns money...

CREATE FUNCTION functionName( @a_principal money, @a_from_date
  datetime, @a_to_date datetime, @a_rate float )  RETURNS money AS BEGIN

  DECLARE @v_dint money   set @v_dint = computation_here
     set @v_dint = round(@v_dint, 2)

  RETURN @v_dint    
END 
GO 
Grant execute on functionName to another_user 
Go


Im just wondering if this is possible to be converted to iTVF?

I've tried doing this but I got an error:

CREATE FUNCTION functionName ( @a_principal money, @a_from_date
  datetime, @a_to_date datetime, @a_rate float )  
RETURNS TABLE AS 
RETURN SELECT returnMoney = computation_here  
GO  
Grant execute on functionName to another_user  Go


ERROR:


  Msg 4606, Level 16, State 1, Line 2 
      Granted or revoked privilege EXECUTE is not compatible with object.


This function is used like this:

update table_name set interest = functionName(col1,col2...) where...


Thanks in advance!
Scalar functions require EXECUTE permissions, however when you've converted to a Table Valued Function the permissions required change to SELECT.

You must now GRANT SELECT ON functionName TO another_user;

From BOL:


  Users other than the owner must be granted EXECUTE permission on a function (if the function is scalar-valued) before they can use it in a Transact-SQL statement. If the function is table-valued, the user must have SELECT permissions on the function before referencing it.