1 files changed, 22 insertions, 3 deletions
diff --git a/libs/util.ml b/libs/util.ml
index 522c3ec..494faac 100644
--- a/libs/util.ml
+++ b/libs/util.ml
@@ -1,11 +1,30 @@
-exception TypeError
+(* Locations *)
+
+type position = Lexing.position
+let position_unknown = Lexing.dummy_pos
+
+type extent = position * position
+let extent_unknown = (position_unknown, position_unknown)
+
+
+(* Exceptions *)
+
+exception NoLocError of string
+let error x = raise (NoLocError x)
+
+exception LocError of extent list * string
+let loc_error l f x =
+  try f x with
+  | NoLocError e -> raise (LocError([l], e))
+  | LocError(q, e) -> raise (LocError(l::q, e))
+
+(* Varmaps *)
 
 module VarMap = Mapext.Make(String)
-exception Duplicate of string
 let disjoint_union k a b = match a, b with
   | Some x, None -> Some x
   | None, Some y -> Some y 
-  | _ -> raise (Duplicate k)
+  | _ -> error ("Duplicate name in disjoint union: " ^ k)
 
 let rec fix equal f s =
   let fs = f s in