unique list

[Maciej Walezak]

Hello there,

I have a list definitions:
dir1 = ../one
dir2 = ../two
dir3 = ../two

It may happen that some variables point to the same directory

Now I would like to have a single list
dirs = $(dir1) $(dir2) $(dir3)

but I need this list to be unique i.e. I need dirs to be: ../one ../two

Has anybody any idea how to do this? Of course dir* definitions can be changed 
any time and dirs shoudl be always correct.

thanks
--
Maciej Walezak
-GDN-