Function returns mutliple rows - HELP

How can I make function returning multiple tuples?

For example:
============
I have a table COMPANY: id_company | company_name | country
-------------------------------------
1 | Company 1 | Germany
2 | Company 2 | Germany
3 | Company 3 | Slovakia
4 | Company 4 | Slovakia
5 | Company 5 | Slovakia
6 | Company 6 | Italy

I need a function returning all 'company IDs' and 'company names'
from 'Slovakia'.
The parameter to the function is 'country'.

Can anybody give me a simple example how to do it using pl/pgsql by
function returning more tuples?

Thanks in advance,
julian

mailto:juleni(at)seznam(dot)cz