MDX coding

I want to compare the value between the syntax code "userName()" and STRToMember("[xxxx].[Username].&[" + UserName() + "]") in SSAS:s calculation, inside of a calculated member.

Unfortunately, I get error message. How should I write the code to make comparision.

IIF
(    
     userName() = STRToMember("[xxxx].[Username].&[" + UserName() + "]"),    
"yes",    
"No"
)