select character type

Here is the situation: I use unlimited polymorphic variable as dummy argument and in select section, how can I select character type with specified length(assume length 1) ? I've tried:

SELECT TYPE(var)
TYPE IS(CHARACTER(1))
   ....
TYPE IS(CHARACTER*1)
   ....
TYPE IS(CHARACTER(LEN=1))
   ....
END SELECT

But none of the above is correct. and only TYPE IS(CHARACTER(*)) can pass the compilation. Appreciate anyone can show me an example.