diff --git a/addressbook.cabal b/addressbook.cabal
index 719827f..cad62e9 100644
--- a/addressbook.cabal
+++ b/addressbook.cabal
@@ -20,6 +20,7 @@ library
   exposed-modules:     MyLib
                      , Data.Email.Header
                      , Data.Email
+                     , Control.Addressbook.Streaming
   -- other-modules:
   -- other-extensions:
   default-extensions:  OverloadedStrings
@@ -42,6 +43,7 @@ executable addressbook
   -- other-modules:
   -- other-extensions:
   build-depends:       base ^>=4.13.0.0, addressbook
+                     , optparse-applicative
   hs-source-dirs:      app
   default-language:    Haskell2010
 
diff --git a/app/Main.hs b/app/Main.hs
index 60d904e..b55c6ee 100644
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -1,8 +1,22 @@
+{-# LANGUAGE LambdaCase #-}
 module Main where
 
-import qualified MyLib (someFunc)
+import Options.Applicative
+
+import qualified Control.Addressbook.Streaming as Streaming
+
+data CmdLine
+  = Stream
+  deriving Show
+
+cmdline :: Parser CmdLine
+cmdline = subparser (command "stream" (info (pure Stream) (progDesc "Record a stream of filenames")))
+
+handler :: CmdLine -> IO ()
+handler = \case
+  Stream -> Streaming.run
 
 main :: IO ()
-main = do
-  putStrLn "Hello, Haskell!"
-  MyLib.someFunc
+main = execParser opts >>= handler
+  where
+    opts = info (cmdline <**> helper) (fullDesc <> progDesc "Email addressbook")
diff --git a/build.sh b/build.sh
new file mode 100755
index 0000000..2892ba0
--- /dev/null
+++ b/build.sh
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+# while :; do
+find addressbook.cabal {src,test,app} -type f | entr -d -r -c -s 'cabal build --ghc-options=-Wall'
+# done
+
diff --git a/default.nix b/default.nix
index c4377c6..53b64d1 100644
--- a/default.nix
+++ b/default.nix
@@ -1,6 +1,7 @@
 { mkDerivation, attoparsec, base, bytestring, bytestring-trie
 , conduit, conduit-extra, hedgehog, hedgehog-corpus, HUnit, lens
-, mtl, stdenv, tasty, tasty-hedgehog, tasty-hunit, text, vector
+, mtl, optparse-applicative, stdenv, tasty, tasty-hedgehog
+, tasty-hunit, text, vector
 }:
 mkDerivation {
   pname = "addressbook";
@@ -12,7 +13,7 @@ mkDerivation {
     attoparsec base bytestring bytestring-trie conduit conduit-extra
     lens mtl text vector
   ];
-  executableHaskellDepends = [ base ];
+  executableHaskellDepends = [ base optparse-applicative ];
   testHaskellDepends = [
     base bytestring conduit conduit-extra hedgehog hedgehog-corpus
     HUnit tasty tasty-hedgehog tasty-hunit text vector
diff --git a/src/Control/Addressbook/Streaming.hs b/src/Control/Addressbook/Streaming.hs
new file mode 100644
index 0000000..e8b6246
--- /dev/null
+++ b/src/Control/Addressbook/Streaming.hs
@@ -0,0 +1,25 @@
+module Control.Addressbook.Streaming where
+
+import qualified Data.Text as T
+
+import Conduit
+import qualified Data.Conduit.Binary as CB
+import qualified Data.Conduit.Combinators as C
+import qualified Data.Conduit.List as CL
+import qualified Data.Conduit.Text as CT
+
+import Data.Email
+import Data.Email.Header
+       (Header)
+
+import System.IO
+       (stdin)
+
+combine :: (MonadResource m, MonadThrow m, MonadIO m) => ConduitM FilePath Header m ()
+combine = await >>= \case
+  Nothing -> pure ()
+  Just path -> (CB.sourceFile path .| parseEmail) >> combine
+
+run :: IO ()
+run = do
+  runResourceT $ runConduit (CB.sourceHandle stdin .| CT.decode CT.utf8 .| CT.lines .| C.map T.unpack .| combine .| C.mapM_ (liftIO . print))