anchor.diff:    idList = import ../system/ids.nix;
   
     optionalString = pkgs.lib.optionalString;
  +  concatStringsSep = pkgs.lib.concatStringsSep;
     mainCf = 
     ''
       queue_directory = /var/postfix/queue
  
positive.code:   +
    (if cfg.networks!=null then
      (''
        mynetworks = ${toString cfg.networks}
      '') 
    else if (cfg.networksStyle != "") then
      (''
  
negative.code:     myorigin = ${cfg.origin}
    '')
    + optionalString (cfg.destination != null) (''
      mydestination = ${concatStringsSep ", " cfg.destination}
    '')
    + optionalString (cfg.relayDomains != null) (''
      relay_domains = ${concatStringsSep ", " cfg.relayDomains}
    '')
    + ''
      local_recipient_maps = 
  