Function returning setof taking parameters from another table

Hello.

I've got a function which returns set of records:

select * from f_test(123);

param |  val1 |  val2
--------------------------- 123   |   1  |  17 123   |   2   |  18



I'd like to execute it multiple times with parameters from other
query, like (it doesn't work of course):

select * from f_test(x.id)
join x on (x.id in (123,124,125));

in order to get:

param |  val1 |  val2
--------------------------- 123   |   1   |  17 123   |   2   |  18 124   |   4   |  179 125   |   13 |  18 125   |
15|  12 125   |   14 |  112
 

So far the only method I can think of is to use union all with
different parametrs, like:

select * from f_test(123)
union all
select * from f_test(124)
union all
select * from f_test(125);

But it is not flexible, I'd like to have parameters stored in another table.

I can also write a pl/pg function, create a string like this with
unions and EXECUTE it. However, it seems ugly to me.

Is there another way?

Regards,
Marcin