{
:local pole                # I want variable "pole" to be an array of mac addresses.
:local filtermac
:local i
:local j

    :local fpravidla [/ip firewall filter find]
    :set i 0
    :foreach j in $fpravidla do={
        :set filtermac [/ip firewall filter get $j value-name=src-mac-address]
        :set i ($i+1)
        :set pole[$i] $filtermac      # how can I write this?    
      }
}

{
	:local pole;
	:foreach j in=[/ip firewall filter find] do={
		:set pole ( $pole , [/ip firewall filter get $j src-mac-address]);
	}
}