Picos can be used with a variety of event generators. When the event generator is a browser, it is useful for a pico to be able to set a cookie in the browser. Then, rules reacting to later events, and queries responding to requests from that same browser will have access to the value of the cookie.

...

Setting a cookie

Here is a KRL rule which causes a cookie to be set in the browser which, as an event generator, sends a matching event:

  rule set_cookie {
    select when cookie needed
    pre {
      eci = wrangler:channelchannels(["wellKnown_Rx","Tx_Rx"]).head(){"id"} || meta:eci;
    }
    every {
      send_directive("_cookie",{"cookie": <<wellKnown_Rx=#{eci}; Path=/sky>>});
    }
  }

...

Line 7 sends a directive with a special name, _cookie. At the conclusion of event processing, the pico engine interprets this directive, and will include the appropriate HTTP "Set-Cookie" header. Upon receipt of the response including this header, a browser will remember the cookie name and value, for future interaction with the same pico engine hostname. 

...

  rule set_cookie {
    select when cookie needed
    pre {
      eci = wrangler:channelchannels(["wellKnown_Rx","Tx_Rx"]).head(){"id"};
    }
    if eci then every {
      send_directive("_cookie",{"cookie": <<wellKnown_Rx=#{eci}; Path=/sky>>});
    }
  }

...