how to found a variable is in a aggregation or not?

[Yi Zhao <yi.zhao@xxxxxxxxxxxxxxx>]

I want to check a variable is in a aggregattion or not, so I create a
function as below:

create or replace function anytest(val text) returns boolean as $$
begin
	perform 1 where quote_literal(val) in ('hello', 'world', 'test');
	if not found then
		return false;
	else
		return true;
	end if;
end;
$$ language plpgsql;

but when I used, I got the result below, why?

test=# select anytest('world111');
 anytest 
---------
 f
(1 row)

test=# select anytest('world');   
 anytest 
---------
 f
(1 row)


any help is appreciated.

regards,
Zy