Incorporate Evaluate into irc

The code is a bit ugly in order to conform with the type system.

ocaml/irc.ml

@@ -4,7 +4,7 @@ module C = Irc_client_lwt.Client
 let host = "irc.freenode.net"
 let port = 6667
 let realname = "CheeseBot"
-let nick = "cheesebot"
+let nick = "cheesebot2"
 let username = nick
 let channel = "#cheeseburger"
 let message = "Hello, world!  This is a test from chesebot"
@@ -16,15 +16,31 @@ let string_opt_to_string = function
 let string_list_to_string string_list =
   Printf.sprintf "[%s]" (String.concat "; " string_list)
 
+let evaluate_string_opt = function
+  | None -> None
+  | Some s -> Evaluate.evaluate s
+
 let callback ~connection ~result =
   let open Irc_message in
   match result with
   | Message {prefix=prefix; command=command; params=params; trail=trail} ->
+    begin
       Lwt_io.printf "Got message: prefix=%s; command=%s; params=%s; trail=%s\n"
         (string_opt_to_string prefix)
         command
         (string_list_to_string params)
-      (string_opt_to_string trail)
+        (string_opt_to_string trail);
+      match command with
+      | "PRIVMSG" -> 
+        begin
+          let response = evaluate_string_opt trail in
+          match response with
+          | None -> Lwt.return_unit
+          | Some s ->
+            C.send_privmsg ~connection ~target:channel ~message:s
+        end
+      | _ -> Lwt.return_unit
+    end
   | Parse_error (raw, error) ->
     Lwt_io.printf "Failed to parse \"%s\" because: %s" raw error