diff --git a/Extraction.v b/Extraction.v
new file mode 100644
index 0000000..2737559
--- /dev/null
+++ b/Extraction.v
@@ -0,0 +1,80 @@
+(** Extraction of computations to OCaml. *)
+Require Import Coq.Lists.List.
+Require Import Coq.Strings.String.
+Require Import Computation.
+Require Import Pervasives.
+Require Import StdLib.
+
+Import ListNotations.
+
+(** * A nice extraction for strings. *)
+Require Import ExtrOcamlBasic.
+Require Import ExtrOcamlString.
+
+(** How to run output events. *)
+Module Output.
+  Module Log.
+    Definition write (message : string) : unit := tt.
+    Extract Constant write => "fun _ -> print_endline ""message""".
+  End Log.
+
+  Module File.
+    Definition read (file_descriptors : unit) (file_name : string) : unit := tt.
+    Extract Constant read => "fun file_descriptors file_name ->
+  let file_name_string = List.fold_right (fun c s -> String.make 1 c ^ s) file_name """" in
+  file_descriptors := (Unix.openfile file_name_string [Unix.O_RDONLY] 0o640, file_name) :: !file_descriptors".
+  End File.
+
+  Module TCPServerSocket.
+    (* TODO *)
+  End TCPServerSocket.
+
+  Definition run (file_descriptors : unit) (output : Output.t) : unit :=
+    match output with
+    | Output.log output =>
+      match output with
+      | Log.Output.write message => Log.write message
+      end
+    | Output.file output =>
+      match output with
+      | File.Output.read file_name =>
+        File.read file_descriptors (File.Name.to_string file_name)
+      end
+    | Output.socket _ => tt (* TODO *)
+    end.
+End Output.
+
+Definition run_ocaml_aux (sig : Signature.t) (mem : Memory.t sig)
+  (start : Memory.t sig -> Memory.t sig * list Output.t)
+  (handler : Input.t -> Memory.t sig -> Memory.t sig * list Output.t)
+  (run : unit -> Output.t -> unit)
+  : unit := tt.
+Extract Constant run_ocaml_aux => "fun _ mem start handler run ->
+  let file_descriptors = ref [] in
+  let (mem, outputs) = start mem in
+  let mem = ref mem in
+  let outputs = ref outputs in
+  while true do
+    List.iter (run file_descriptors) !outputs;
+    let (reads, _, _) = Unix.select (List.map fst !file_descriptors) [] [] (-1.) in
+    List.iter (fun read ->
+      let file_name = List.assoc read !file_descriptors in
+      match File.Name.of_string file_name with
+      | None -> ()
+      | Some file_name ->
+        let input = Input.Coq_file (File.Input.Coq_read (file_name, ['c'; 'o'; 'n'; 't'; 'e'; 'n'; 't'])) in
+        let (mem', outputs') = handler input !mem in
+        mem := mem';
+        outputs := outputs' @ !outputs)
+      reads
+  done".
+
+Definition run_ocaml (sig : Signature.t) (mem : Memory.t sig)
+  (start : unit -> C sig unit) (handler : Input.t -> C sig unit) : unit :=
+  let last tuple :=
+    match tuple with
+    | (x, y, z) => (y, z)
+    end in
+  run_ocaml_aux sig mem (fun mem => last (C.run mem (start tt)))
+    (fun input mem => last (C.run mem (handler input)))
+    Output.run.
\ No newline at end of file
diff --git a/HttpServer.v b/HttpServer.v
index 449cd91..c8e3217 100644
--- a/HttpServer.v
+++ b/HttpServer.v
@@ -38,13 +38,7 @@ Module Url.
     Some (new url).
 
   Definition to_file_name (url : t) : option File.Name.t :=
-    let names : list string := String.split (to_string url) "/" in
-    match List.rev names with
-    | base :: path => Some {|
-      File.Name.path := List.rev path;
-      File.Name.base := base |}
-    | [] => None
-    end.
+    File.Name.of_string (to_string url).
 End Url.
 
 (** Parse an HTTP request. *)
@@ -192,4 +186,11 @@ User-Agent: CERN-LineMode/2.15 libwww/2.17b3".
     Output.log (Log.Output.write "File info/contact.html requested");
     Output.log (Log.Output.write "Client connection accepted.");
     Output.socket (TCPServerSocket.Output.bind 80)].
-End Test.
\ No newline at end of file
+End Test.
+
+(** * Tests of the extraction. *)
+Require Import Extraction.
+
+Definition test : unit := run_ocaml _ (Memory.Cons Clients.empty Memory.Nil)
+  start handler.
+Extraction "test" test.
\ No newline at end of file
diff --git a/Make b/Make
index 0766ceb..da5ab26 100644
--- a/Make
+++ b/Make
@@ -3,6 +3,7 @@
 
 # Compilation units
 Computation.v
+Extraction.v
 HttpServer.v
 Pervasives.v
 StdLib.v
diff --git a/Pervasives.v b/Pervasives.v
index 27caccc..b31a842 100644
--- a/Pervasives.v
+++ b/Pervasives.v
@@ -1,7 +1,11 @@
 (** Basic type and event definitions. *)
+Require Import Coq.Lists.List.
 Require Import Coq.Strings.String.
 Require Import String.
 
+Import ListNotations.
+Open Local Scope string.
+
 (** Events to log data. *)
 Module Log.
   Module Output.
@@ -24,12 +28,27 @@ Module File.
       List.fold_right (fun x y => (x ++ "/" ++ y) % string) (base file_name)
         (path file_name).
 
+    Check eq_refl : to_string {|
+      path := ["some"; "dir"];
+      base := "file.txt" |} =
+      "some/dir/file.txt".
+
     (** Test equality. *)
     Definition eqb (file_name1 file_name2 : t) : bool :=
       if List.list_eq_dec string_dec (path file_name1) (path file_name2) then
         String.eqb (base file_name1) (base file_name2)
       else
         false.
+
+    (** Parse a string into a file name. *)
+    Definition of_string (file_name : string) : option t :=
+      let names : list string := String.split file_name "/" in
+      match List.rev names with
+      | base :: path => Some {|
+        File.Name.path := List.rev path;
+        File.Name.base := base |}
+      | [] => None
+      end.
   End Name.
 
   (** Incoming events. *)