2 files changed, 9 insertions, 3 deletions
diff --git a/lib/protocols/Handle.ml b/lib/protocols/Handle.ml
index 378b8c8..41c88dd 100644
--- a/lib/protocols/Handle.ml
+++ b/lib/protocols/Handle.ml
@@ -3,14 +3,16 @@ type protocol = ..
 module Error = struct
   open Concepts.Condition
 
-  let unimplemented_protocol () = condition "unimplemented-protocol" "A required protocol was not implemented by the specified object"
-                                    empty
+  let unimplemented_protocol obj_name =
+    condition "unimplemented-protocol" "A required protocol was not implemented by the specified object"
+      ("object" |=| Concepts.Value.String obj_name)
 end
 
 class type obj = object
   method reference : bool
   method release : unit
   method hash : Concepts.Hash.hash
+  method to_string : string
   method protocols : protocol list
 end
 
@@ -51,9 +53,11 @@ let equal h1 h2 =
 let hash h = (object_of h)#hash
 let protocols h = (object_of h)#protocols
 
+let to_string h = (object_of h)#to_string
+
 let release ({ valid; _ } as handle) =
   let o = object_of handle in
   valid := false;
   o#release
 
-let require f h = Option.to_result ~none:(Error.unimplemented_protocol ()) (f h)
+let require f h = Option.to_result ~none:(Error.unimplemented_protocol (to_string h)) (f h)
diff --git a/lib/protocols/Handle.mli b/lib/protocols/Handle.mli
index c5c0d6a..40a78ff 100644
--- a/lib/protocols/Handle.mli
+++ b/lib/protocols/Handle.mli
@@ -8,6 +8,7 @@ class type obj = object
   method reference : bool
   method release : unit
   method hash : Concepts.Hash.hash
+  method to_string : string
   method protocols : protocol list
 end
 
@@ -24,5 +25,6 @@ val release : t -> unit
 
 val hash : t -> Concepts.Hash.hash
 val protocols : t -> protocol list
+val to_string : t -> string
 
 val require : (t -> 'a interface option) -> t -> ('a interface, Concepts.Condition.condition) result