diff --git a/src/core/env.ml b/src/core/env.ml
index 57ec4f1465a2966970504a736bd99682fe249920..14665fe3066cc6e2ef32646593f3bf53a7a5b696 100644
--- a/src/core/env.ml
+++ b/src/core/env.ml
@@ -22,7 +22,7 @@ open Theory
 
 (** Environment *)
 
-type retrieve_channel = string list -> in_channel
+type retrieve_channel = string list -> string * in_channel
 
 type env = {
   env_ret_chan : retrieve_channel;
diff --git a/src/core/env.mli b/src/core/env.mli
index c4d7099c99bf8fc829479faba5aecc9ce2e2f5a9..973120458fab4ed8cf282f4f03e8ffcc4d7bcd8b 100644
--- a/src/core/env.mli
+++ b/src/core/env.mli
@@ -27,7 +27,9 @@ val env_tag : env -> Hashweak.tag
 
 module Wenv : Hashweak.S with type key = env
 
-type retrieve_channel = string list -> in_channel
+type retrieve_channel = string list -> string * in_channel
+  (** retrieves a channel from a given path; a filename is also returned, 
+      for printing purposes only *)
 
 type retrieve_theory  = env -> string list -> theory Mnm.t
 
@@ -39,7 +41,7 @@ val find_theory : env -> string list -> string -> theory
   (** [find_theory e p n] finds the theory named [p.n] in environment [e]
       @raise TheoryNotFound if theory not present in env [e] *)
 
-val find_channel : env -> string list -> in_channel
+val find_channel : env -> string list -> string * in_channel
 
 (** Parsers *)
 
diff --git a/src/parser/lexer.mll b/src/parser/lexer.mll
index 1ec4b7bfa786fd104ac14795a1e0945eded98208..7324f2326ba2dd180b7a1c5e008b2a394c493c97 100644
--- a/src/parser/lexer.mll
+++ b/src/parser/lexer.mll
@@ -282,7 +282,8 @@ and string = parse
   let create_env lp =
     let ret_chan sl = 
       let f = List.fold_left Filename.concat "" sl in
-      open_in (locate_file lp f)
+      let file = locate_file lp f in
+      file, open_in file
     in
     let retrieve env sl =
       let f = List.fold_left Filename.concat "" sl ^ ".why" in
diff --git a/src/programs/pgm_env.ml b/src/programs/pgm_env.ml
index 028924bd9733463a6818dc6a1d45bb594bb48838..1daeef87688a40b21b8b6572263075eee4c60b70 100644
--- a/src/programs/pgm_env.ml
+++ b/src/programs/pgm_env.ml
@@ -8,7 +8,7 @@ type t = {
   memo     : (string list, Pgm_module.t Mnm.t) Hashtbl.t;
 }
 
-and retrieve_module = t -> in_channel -> Pgm_module.t Mnm.t
+and retrieve_module = t -> string -> in_channel -> Pgm_module.t Mnm.t
 
 let get_env penv = penv.env
 
@@ -29,8 +29,8 @@ let find_library penv sl =
   try Hashtbl.find penv.memo sl
   with Not_found ->
     Hashtbl.add penv.memo sl Mnm.empty;
-    let c = Env.find_channel penv.env (add_suffix sl) in
-    let m = penv.retrieve penv c in
+    let file, c = Env.find_channel penv.env (add_suffix sl) in
+    let m = penv.retrieve penv file c in
     close_in c;
     Hashtbl.replace penv.memo sl m;
     m
diff --git a/src/programs/pgm_env.mli b/src/programs/pgm_env.mli
index b97b4242025f73165c62165fbb318a0dc145ca65..2bf62d907bff54e94a96efa40e797c50aedde888 100644
--- a/src/programs/pgm_env.mli
+++ b/src/programs/pgm_env.mli
@@ -6,7 +6,7 @@ type t
 
 val get_env : t -> Env.env
 
-type retrieve_module = t -> in_channel -> Pgm_module.t Mnm.t
+type retrieve_module = t -> string -> in_channel -> Pgm_module.t Mnm.t
 
 val create : Env.env -> retrieve_module -> t
 
diff --git a/src/programs/pgm_main.ml b/src/programs/pgm_main.ml
index 92e71c19d6ae2355f1cdcd8984a746da08b9ac95..0f313dbe9cb7b84a0f68f43c9977ed4425e2f37c 100644
--- a/src/programs/pgm_main.ml
+++ b/src/programs/pgm_main.ml
@@ -33,10 +33,18 @@ let add_module ?(type_only=false) env penv lmod m =
   let uc = create_module (Ident.id_user id.id id.id_loc) in
   let uc = List.fold_left (Pgm_typing.decl ~wp env penv lmod) uc m.mod_decl in
   let m = close_module uc in
-  Mstr.add id.id m lmod
+  Mnm.add id.id m lmod
 
-let retrieve penv c =
-  assert false (*TODO*)
+let retrieve penv file c =
+  let lb = Lexing.from_channel c in
+  Loc.set_file file lb;
+  let ml = Pgm_lexer.parse_file lb in
+  if Debug.test_flag Typing.debug_parse_only then
+    Mnm.empty
+  else
+    let type_only = Debug.test_flag Typing.debug_type_only in
+    let env = Pgm_env.get_env penv in
+    List.fold_left (add_module ~type_only env penv) Mnm.empty ml
 
 let pgm_env_of_env =
   let h = Env.Wenv.create 17 in
@@ -49,19 +57,11 @@ let pgm_env_of_env =
       penv
 
 let read_channel env file c =
-  let lb = Lexing.from_channel c in
-  Loc.set_file file lb;
-  let ml = Pgm_lexer.parse_file lb in
-  if Debug.test_flag Typing.debug_parse_only then
-    Theory.Mnm.empty
-  else begin
-    let type_only = Debug.test_flag Typing.debug_type_only in
-    let penv = pgm_env_of_env env in
-    let mm = List.fold_left (add_module ~type_only env penv) Mstr.empty ml in
-    Mstr.fold 
-      (fun _ m tm -> Theory.Mnm.add m.m_name.id_string m.m_th tm) 
-      mm Theory.Mnm.empty
-  end
+  let penv = pgm_env_of_env env in
+  let mm = retrieve penv file c in
+  Mnm.fold 
+    (fun _ m tm -> Theory.Mnm.add m.m_name.id_string m.m_th tm) 
+    mm Theory.Mnm.empty
 
 let () = Env.register_format "whyml" ["mlw"] read_channel
 
diff --git a/src/programs/pgm_typing.ml b/src/programs/pgm_typing.ml
index 60fd721d1598cb05c80fade3f3d282cca18e38c4..e7d0aa180708e3550906aef4fbc052c11a35491b 100644
--- a/src/programs/pgm_typing.ml
+++ b/src/programs/pgm_typing.ml
@@ -133,6 +133,7 @@ let specialize_global loc x uc =
   let p = ns_find_pr (namespace uc) x in
   p.p_ls, specialize_type_v ~loc (Htv.create 17) p.p_tv
 
+let dot fmt () = pp_print_string fmt "."
 let print_qualids = print_list dot pp_print_string
 let print_qualid fmt q = 
   print_list dot pp_print_string fmt (Typing.string_list_of_qualid [] q)
@@ -140,7 +141,7 @@ let print_qualid fmt q =
 let specialize_exception loc x uc =
   let s = 
     try ns_find_ex (namespace uc) x
-    with Not_found -> errorm ~loc "unbound exception %a" print_qualids x
+    with Not_found -> errorm ~loc "@[unbound exception %a@]" print_qualids x
   in
   match Denv.specialize_lsymbol ~loc s with
     | tyl, Some ty -> s, tyl, ty
@@ -1307,7 +1308,7 @@ let cannot_be_generalized gl = function
 let find_module penv lmod q id = match q with
   | [] ->
       (* local module *)
-      Mstr.find id lmod
+      Mnm.find id lmod
   | _ :: _ ->
       (* theory in file f *)
       Pgm_env.find_module penv q id
@@ -1364,8 +1365,8 @@ let rec decl ~wp env penv lmod uc = function
       let m =
 	try
 	  find_module penv lmod q id
-	with Not_found -> 
-	  errorm ~loc "unbound module %a" print_qualid qid
+	with Not_found | Pgm_env.ModuleNotFound _ -> 
+	  errorm ~loc "@[unbound module %a@]" print_qualid qid
       in
       let n = match use_as with
 	| None -> Some (m.m_name.id_string)
diff --git a/src/programs/pgm_typing.mli b/src/programs/pgm_typing.mli
index 68cfebd9f77fccd79919f7f0033bbd588f9779f7..ea5db93ee1ed5e4a24f103c85596f95d2ae9d1c1 100644
--- a/src/programs/pgm_typing.mli
+++ b/src/programs/pgm_typing.mli
@@ -23,7 +23,7 @@ open Util
 val debug : Debug.flag
 
 val decl : 
-  wp:bool -> Env.env -> Pgm_env.t -> Pgm_module.t Mstr.t -> 
+  wp:bool -> Env.env -> Pgm_env.t -> Pgm_module.t Pgm_module.Mnm.t -> 
   Pgm_module.uc -> Pgm_ptree.decl -> Pgm_module.uc
 
 val print_post : Format.formatter -> Pgm_ttree.post -> unit
diff --git a/tests/test-pgm-jcf.mlw b/tests/test-pgm-jcf.mlw
index 9ec5562c4973396455e0f8c2e1fe93fb56a1eaa6..a09b247dcf8c266771122bacd8aeb80ba946d9ae 100644
--- a/tests/test-pgm-jcf.mlw
+++ b/tests/test-pgm-jcf.mlw
@@ -1,24 +1,14 @@
 
-module R
-
-  { use import programs.Prelude }
-
-  parameter ref : v:'a -> {} ref 'a { !result = v }
-
-  parameter set : r:ref 'a -> v:'a -> {} unit writes r { !r = v }
-
-end
-
 module P
 
   { use import programs.Prelude }
 
-  use module R
+  use module import pervasives.Ref 
 
   let test () =
     { true }
-    let r = R.ref 0 in
-    R.set r 1;
+    let r = ref 0 in
+    set r 1;
     !r
     { result > 0 }
 
diff --git a/theories/pervasives.mlw b/theories/pervasives.mlw
new file mode 100644
index 0000000000000000000000000000000000000000..d44174b8ece49a2d30b8bdc0a0ea112f969203e3
--- /dev/null
+++ b/theories/pervasives.mlw
@@ -0,0 +1,10 @@
+module Ref
+
+  { use import programs.Prelude }
+
+  parameter ref : v:'a -> {} ref 'a { !result = v }
+
+  parameter set : r:ref 'a -> v:'a -> {} unit writes r { !r = v }
+
+end
+