module IVarMap:Fix.IMPERATIVE_MAPSwith type key = var
VarMap, in the form expected by Fix.type key
type 'data t
val create : unit -> 'data tval clear : 'data t -> unitval add : key -> 'data -> 'data t -> unitval find : key -> 'data t -> 'dataval iter : (key -> 'data -> unit) ->
'data t -> unit