create or replace function fupper(text)
  returns text as
'
  select upper($1::char) || lower(substring($1 from 2 for length($1)))
' language sql;

create or replace function super_mega_function(text, text)
  returns text as
'
declare
  f_name alias for $1;
  arg alias for $2;
  rec record;
begin
  for rec in execute
    ''select '' || f_name || ''('' || quote_literal(arg) || '') as value''
  loop
    return rec.value;
  end loop;
end;
' language plpgsql;

select 'fupper', super_mega_function('fupper', 'TeSt')
union
select 'lower', super_mega_function('lower', 'TeSt')
union
select 'upper', super_mega_function('upper', 'TeSt')