diff --git a/infer/src/quandary/Trace.ml b/infer/src/quandary/Trace.ml
new file mode 100644
index 000000000..4065d6b17
--- /dev/null
+++ b/infer/src/quandary/Trace.ml
@@ -0,0 +1,93 @@
+(*
+ * Copyright (c) 2016 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *)
+
+open! Utils
+
+module F = Format
+module L = Logging
+
+module type Spec = sig
+  module Source : Source.S
+  module Sink : Sink.S
+
+  (** should a flow originating at source and entering sink be reported? *)
+  val should_report : Source.t -> Sink.t -> bool
+end
+
+module type S = sig
+  include Spec
+  type t
+
+  (** get the source of the trace *)
+  val source : t -> Source.t
+
+  (** get the sink of the trace, if any *)
+  val sink : t -> Sink.t option
+
+  (** return true if this trace represent a dangerous flow *)
+  val should_report : t -> bool
+
+  (** create a trace from a source *)
+  val of_source : Source.t -> t
+
+  (** add a sink to the current trace. *)
+  val add_sink : t -> Sink.t -> t
+
+  val compare : t -> t -> int
+  val pp : F.formatter -> t -> unit
+end
+
+module Make (Spec : Spec) = struct
+  include Spec
+
+  type t =
+    {
+      source : Source.t; (** last function in the trace that returned tainted data *)
+      sink : Sink.t option;
+      (** last callee in the trace that transitively called a tainted function (if any) *)
+      passthroughs : Passthrough.Set.t; (** calls that occurred between source and sink *)
+    }
+
+  let compare t1 t2 =
+    let compare_sink_opts sink1_opt sink2_opt = match sink1_opt, sink2_opt with
+      | Some sink1, Some sink2 -> Sink.compare sink1 sink2
+      | None, None -> 0
+      | Some _, None -> (-1)
+      | None, Some _ -> 1 in
+    Source.compare t1.source t2.source
+    |> next compare_sink_opts t1.sink t2.sink
+    |> next Passthrough.Set.compare t1.passthroughs t2.passthroughs
+
+  let pp fmt t =
+    let pp_sink_opt fmt = function
+      | None -> F.fprintf fmt "?"
+      | Some sink -> Sink.pp fmt sink in
+    F.fprintf
+      fmt
+      "%a -> %a via %a"
+      Source.pp t.source pp_sink_opt t.sink Passthrough.Set.pp t.passthroughs
+
+  let source t =
+    t.source
+
+  let sink t =
+    t.sink
+
+  let should_report t = match t.sink with
+    | Some sink -> Spec.should_report t.source sink
+    | None -> false
+
+  let of_source source =
+    let passthroughs = Passthrough.Set.empty in
+    let sink = None in
+    { source; passthroughs; sink; }
+
+  let add_sink t sink =
+    { t with sink = Some sink; }
+end