passing array as argument and returning an array in plpgsql

Hi all,
       I am using postgresql7.4. How to handle arrays in plpgsql. How can
I pass an array. Is it possible to retrieve values from an array by
indexing it like

argument : '{1,2,3}'
Return value : varchar array

Variables :
---------

a alias for $1
b _varchar

Usage :
-----

b[1] = a[1];
b[2] = a[2];

return b;

Is it possible.

TIA,

--
regards,
Deepa K