=== modified file '.merlin'
--- .merlin	2019-04-12 23:47:50 +0000
+++ .merlin	2019-04-11 14:01:44 +0000
@@ -1,10 +1,8 @@
 S .
 B _build
 PKG core
+PKG async
 PKG core_extended
-PKG lwt
-PKG lwt.unix
-PKG lwt_ppx
 PKG ppx_let
 PKG ppx_deriving
 PKG ppx_deriving.show

=== modified file 'Makefile'
--- Makefile	2019-04-12 23:47:50 +0000
+++ Makefile	2019-04-12 00:15:26 +0000
@@ -6,5 +6,5 @@
 ppio.bc: subprocess.cmo ppio.cmo compile
 	./compile subprocess.cmo ppio.cmo -o ppio.bc
 
-%.cmo: %.ml compile
+%.cmx: %.ml compile
 	./compile -c $<

=== modified file 'compile'
--- compile	2019-04-12 23:47:50 +0000
+++ compile	2019-04-12 00:15:26 +0000
@@ -2,13 +2,12 @@
 set -x
 exec ocamlfind ocamlc \
 	-linkpkg \
+	-package async \
+	-package async_unix \
 	-package core \
 	-package base \
-	-package lwt \
-	-package lwt.unix \
-	-package ppx_let \
 	-package ppx_deriving \
 	-package ppx_deriving.show \
-	-package lwt_ppx \
+	-package ppx_let \
 	-thread \
 	"$@"

=== modified file 'ppio.ml'
--- ppio.ml	2019-04-12 23:47:50 +0000
+++ ppio.ml	2019-04-12 00:15:26 +0000
@@ -1,6 +1,7 @@
 (* vim: fileencoding=utf8 ft=ocaml et sw=2 ts=4 sts=4 *)
 
 open Core
+(* open Async *)
 
 let do_echo_prompt () =
   Out_channel.output_string stdout "prompt: ";
@@ -58,59 +59,66 @@
 
 (* Copy data from the reader to the writer, using the provided buffer
    as scratch space *)
-let rec copy_blocks bufsize buffer r w cb () =
-  Lwt.bind (Lwt_unix.read r buffer 0 bufsize) (fun bytes_read ->
-  if bytes_read > 0 then (
-    cb bytes_read buffer;
-      Lwt.bind
-        (Lwt_io.write_from_exactly w buffer 0 bytes_read)
-        (copy_blocks bufsize buffer r w cb)
-  ) else (
-    cb 0 buffer;
-    Lwt_io.close w
-  ))
+let rec copy_blocks buffer r w cb =
+  let open Async in
+  Reader.read r buffer
+  >>= function
+  | `Eof ->
+      cb 0 buffer;
+      Reader.close r
+  | `Ok bytes_read ->
+      cb bytes_read buffer;
+      Writer.write w (Bytes.to_string buffer) ~len:bytes_read;
+      Writer.flushed w
+      >>= fun () ->
+      copy_blocks buffer r w cb
 ;;
 
-let copy_cb fd_in fd_out cb = 
-  let bufsize = 16 * 1024 in
+let copy_cb info fd_in fd_out cb = 
   (* let buffer = Bytes.to_string (Bytes.create (16 * 1024)) in *)
-  let buffer = Bytes.create bufsize in
-  copy_blocks bufsize buffer fd_in (Lwt_io.of_fd Lwt_io.Output fd_out) cb ()
+  let buffer = Bytes.create (16 * 1024) in
+  let create file_descr kind =
+    Async.Unix.Fd.create Fifo file_descr (Info.tag info ~tag:kind)
+  in
+  copy_blocks
+    buffer
+    (Async.Reader.create (create fd_in "reader"))
+    (Async.Writer.create (create fd_out "writer"))
+    cb
 ;;
 
 let cb_null (len:int) (buf:Bytes.t) = ();;
 
 let main {hideendl; endl; color; exe} =
   pe ((show_cmd_args {hideendl; endl; color; exe})^"\n");
-  Lwt_unix.set_default_async_method Lwt_unix.Async_none;
-  let fd0 = Lwt_unix.stdin in
-  let fd1 = Lwt_unix.stdout in
-  let stdin_r, stdin_w = Lwt_unix.pipe_out () in
-  let stdout_r, stdout_w = Lwt_unix.pipe_in () in
+  let fd0 = Unix.File_descr.of_int 0 in
+  let fd1 = Unix.File_descr.of_int 1 in
+  let stdin_r, stdin_w = Unix.pipe () in
+  let stdout_r, stdout_w = Unix.pipe () in
   printf "pipes: (%d %d) (%d %d)\n%!" 
-    (Unix.File_descr.to_int stdin_r)
-    (Unix.File_descr.to_int (Lwt_unix.unix_file_descr stdin_w))
-    (Unix.File_descr.to_int (Lwt_unix.unix_file_descr stdout_r))
-    (Unix.File_descr.to_int stdout_w)
+    (Core.Unix.File_descr.to_int stdin_r)
+    (Core.Unix.File_descr.to_int stdin_w)
+    (Core.Unix.File_descr.to_int stdout_r)
+    (Core.Unix.File_descr.to_int stdout_w)
   ;
   let pid = Subprocess.create_process
     ~redirects:[
-      Lwt_unix.unix_file_descr fd0, Subprocess.Redirect stdin_r;
-      Lwt_unix.unix_file_descr fd1, Subprocess.Redirect stdout_w;
-      Lwt_unix.unix_file_descr stdin_w, Subprocess.Close;
-      Lwt_unix.unix_file_descr stdout_r, Subprocess.Close;
+      fd0, Subprocess.Redirect stdin_r;
+      fd1, Subprocess.Redirect stdout_w;
+      stdin_w, Subprocess.Close;
+      stdout_r, Subprocess.Close;
     ]
     (List.nth_exn exe 0) (List.to_array exe)
   in
   printf "pid: %d\n%!" pid;
-  Lwt_unix.set_blocking ~set_flags:true fd0 false;
-  Lwt_unix.set_blocking ~set_flags:true fd1 false;
-  Lwt_main.run (Lwt.join [
-    copy_cb fd0 stdin_w cb_null;
-    copy_cb stdout_r fd1 cb_null;
-  ]);
-  let _, status = Subprocess.waitpid [] pid in
-  exit (Subprocess.wait_estatus status);
+  let open Async in
+  Deferred.all_unit [
+    copy_cb (Info.of_string "stdin") fd0 stdin_w cb_null;
+    copy_cb (Info.of_string "stdout") stdout_r fd1 cb_null;
+  ] >>= (fun () ->
+    let _, status = Subprocess.waitpid [] pid in
+    exit (Subprocess.wait_estatus status);
+  )
 ;;
 
 let cmd =
@@ -120,7 +128,7 @@
         | true -> Some value
         | false -> None)
   in
-  Command.basic ~summary:"Pretty print I/O to a spawned command."
+  Async.Command.async ~summary:"Pretty print I/O to a spawned command."
   [%map_open
     let hide = flag "-H" ~aliases:["--hide-newlines"] no_arg
       ~doc:"Suppress printing codes of the line-terminating sequence"