dynamic SQL/plsql functions

I have a large list ot parameters and I'd like to have just one main
function for checking them all.  Like so:

check_param(some_identifier_for_the_param, param_value)
...   rec RECORD;
...  select into rec check_param_function  from param_check_table  where id == identifier;
  select rec.check_param_function(param_value) as result;
...


That's the general idea. Is there a way to dynamically call a plsql or sql
function? Is there a way to do what I have above (evaluating a string
before a SQL statement gets sent to postgres)?

Thanks,

R.