$var = "Yes"
IIf($var = "Yes", CallYess(), CallNo())
Function CallYess()
    "Yes" ?
    $CallYess = "True"
EndFunction
Function CallNo()
    "No" ?
    $CallNo = "False"
EndFunction

OK, I see.
AFAIK "If...Then...Else...EndIf" does not have this problem.