add some basic logging

src/blocking_IO.ml

@@ -18,8 +18,12 @@ let spawn f =
   let run () =
     try f()
     with e ->
-      Printf.eprintf "linol: uncaught exception in `spawn`:\n%s\n%!"
+      let msg =
-        (Printexc.to_string e);
+        Printf.sprintf "linol: uncaught exception in `spawn`:\n%s\n%!"
+          (Printexc.to_string e)
+      in
+      !Jsonrpc2._log (fun () -> msg);
+      Printf.eprintf "%s\n%!" msg;
       raise e
 in
   ignore (Thread.create run () : Thread.t)

src/jsonrpc2.ml

@@ -10,6 +10,8 @@ type json = Yojson.Safe.t
 
 module type IO = Sigs.IO
 
+let _log : ((unit -> string) -> unit) ref = ref (fun _ -> ())
+
 module type S = sig
   module IO : IO
 

src/jsonrpc2.mli

@@ -30,3 +30,7 @@ module type S = sig
 end
 
 module Make(IO : IO) : S with module IO = IO
+
+(**/**)
+val _log : ((unit -> string) -> unit) ref
+(**/**)