diff --git a/src/context/lookup.ml b/src/context/lookup.ml
new file mode 100644
index 00000000000..09096ea87ab
--- /dev/null
+++ b/src/context/lookup.ml
@@ -0,0 +1,63 @@
+
+class virtual ['key,'value] lookup = object(self)
+	method virtual add : 'key -> 'value -> unit
+	method virtual remove : 'key -> unit
+	method virtual find : 'key -> 'value
+	method virtual iter : ('key -> 'value -> unit) -> unit
+	method virtual fold : 'acc . ('key -> 'value -> 'acc -> 'acc) -> 'acc -> 'acc
+	method virtual mem : 'key -> bool
+	method virtual clear : unit
+end
+
+class ['key,'value] pmap_lookup = object(self)
+	inherit ['key,'value] lookup
+	val mutable lut : ('key,'value) PMap.t = PMap.empty
+
+	method add (key : 'key) (value : 'value) =
+		lut <- PMap.add key value lut
+
+	method remove (key : 'key) =
+		lut <- PMap.remove key lut
+
+	method find (key : 'key) : 'value =
+		PMap.find key lut
+
+	method iter (f : 'key -> 'value -> unit) =
+		PMap.iter f lut
+
+	method fold : 'acc . ('key -> 'value -> 'acc -> 'acc) -> 'acc -> 'acc = fun f acc ->
+		PMap.foldi f lut acc
+
+	method mem (key : 'key) =
+		PMap.mem key lut
+
+	method clear =
+		lut <- PMap.empty
+end
+
+class ['key,'value] hashtbl_lookup = object(self)
+	inherit ['key,'value] lookup
+	val lut : ('key,'value) Hashtbl.t = Hashtbl.create 0
+
+	method add (key : 'key) (value : 'value) =
+		Hashtbl.replace lut key value
+
+	method remove (key : 'key) =
+		Hashtbl.remove lut key
+
+	method find (key : 'key) : 'value =
+		Hashtbl.find lut key
+
+	method iter (f : 'key -> 'value -> unit) =
+		Hashtbl.iter f lut
+
+	method fold : 'acc . ('key -> 'value -> 'acc -> 'acc) -> 'acc -> 'acc = fun f acc ->
+		Hashtbl.fold f lut acc
+
+	method mem (key : 'key) =
+		Hashtbl.mem lut key
+
+	method clear =
+		Hashtbl.clear lut
+end
+