Compare a variable to a list

I tried to use the matchclass command initially. However, it doesn't appear that the matchclass command will allow me to compare a variable to alist. One of the values used must be a fixed or specified value. The iRule engine keeps giving me the error that all variables must be proceeded by a $. But my syntax is correct according to examples. Here is my sample line...

 

 

set appid [session lookup ssl [SSL::sessionid]]

 

if {matchclass "$appid" != $::app_id}{

 

 

I have tried both removing and including quotes, brackets and braces to isolate the different components. It seems that the matchclass command must have one variable and one known value.