User-defined function question

I have a package, in which I've defined some functions.

I'm trying to use one of these functions in a cursor within one of the package's procedures, but keep getting error messages when I try & create the package:

"PLS-00320: the declaration of the type of this expression is
incomplete or malformed"

and

"PLS-00231: function <func name> may not be used in SQL"

The cursor statement in the procedure is thus:

CURSOR ccursor_name
(parameter IN VARCHAR2)
IS
  SELECT 'x'
  FROM table
  WHERE function(column) = function(parameter);

Thanks for any assistance. My guess is that you can't use user-defined functions in cursor declarations, but I'd be grateful of any clarification.

--
Noah Arc
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