diff --git a/app/Niv.hs b/app/Niv.hs
index 2339df1..b91394b 100644
--- a/app/Niv.hs
+++ b/app/Niv.hs
@@ -11,7 +11,7 @@ import Control.Applicative
 import Control.Monad
 import Control.Monad.State
 import Data.Aeson (FromJSON, FromJSONKey, ToJSON, ToJSONKey)
-import Data.Char (isSpace, toUpper)
+import Data.Char (isSpace)
 import Data.FileEmbed (embedFile)
 import Data.Functor ((<&>))
 import Data.Hashable (Hashable)
@@ -29,6 +29,7 @@ import qualified Data.ByteString.Char8 as B8
 import qualified Data.ByteString.Lazy as L
 import qualified Data.HashMap.Strict as HMap
 import qualified Data.Text as T
+import qualified Data.Text.IO as T
 import qualified GitHub as GH
 import qualified GitHub.Data.Name as GH
 import qualified Options.Applicative as Opts
@@ -70,7 +71,7 @@ getSources = do
           forM (HMap.toList obj) $ \(k, v) ->
             case v of
               Aeson.Object v' ->
-                pure $ HMap.singleton (PackageName (T.unpack k)) (PackageSpec v')
+                pure $ HMap.singleton (PackageName k) (PackageSpec v')
               _ -> abortAttributeIsntAMap
       Just _ -> abortSourcesIsntAMap
       Nothing -> abortSourcesIsntJSON
@@ -78,7 +79,7 @@ getSources = do
 setSources :: Sources -> IO ()
 setSources sources = encodeFile pathNixSourcesJson sources
 
-newtype PackageName = PackageName { unPackageName :: String }
+newtype PackageName = PackageName { unPackageName :: T.Text }
   deriving newtype (Eq, Hashable, FromJSONKey, ToJSONKey, Show)
 
 parsePackageName :: Opts.Parser PackageName
@@ -93,7 +94,7 @@ parsePackageSpec =
     (PackageSpec . HMap.fromList . fmap fixupAttributes) <$>
       many parseAttribute
   where
-    parseAttribute :: Opts.Parser (String, String)
+    parseAttribute :: Opts.Parser (T.Text, T.Text)
     parseAttribute =
       Opts.option (Opts.maybeReader parseKeyVal)
         ( Opts.long "attribute" <>
@@ -115,32 +116,32 @@ parsePackageSpec =
         ))
 
     -- Parse "key=val" into ("key", "val")
-    parseKeyVal :: String -> Maybe (String, String)
+    parseKeyVal :: String -> Maybe (T.Text, T.Text)
     parseKeyVal str = case span (/= '=') str of
-      (key, '=':val) -> Just (key, val)
+      (key, '=':val) -> Just (T.pack key, T.pack val)
       _ -> Nothing
 
     -- Shortcuts for common attributes
-    shortcutAttributes :: Opts.Parser (String, String)
+    shortcutAttributes :: Opts.Parser (T.Text, T.Text)
     shortcutAttributes = foldr (<|>) empty $ mkShortcutAttribute <$>
       [ "branch", "owner", "repo", "version" ]
 
-    mkShortcutAttribute :: String -> Opts.Parser (String, String)
+    mkShortcutAttribute :: T.Text -> Opts.Parser (T.Text, T.Text)
     mkShortcutAttribute = \case
-      attr@(c:_) -> (attr,) <$> Opts.strOption
-        ( Opts.long attr <>
+      attr@(T.uncons -> Just (c,_)) -> (attr,) <$> Opts.strOption
+        ( Opts.long (T.unpack attr) <>
           Opts.short c <>
-          Opts.metavar (toUpper <$> attr) <>
+          Opts.metavar (T.unpack $ T.toUpper attr) <>
           Opts.help
-            (
+            ( T.unpack $
               "Equivalent to --attribute " <>
-              attr <> "=<" <> (toUpper <$> attr) <> ">"
+              attr <> "=<" <> (T.toUpper attr) <> ">"
             )
         )
       _ -> empty
 
-    fixupAttributes :: (String, String) -> (T.Text, Aeson.Value)
-    fixupAttributes (k, v) = (T.pack k, Aeson.String (T.pack v))
+    fixupAttributes :: (T.Text, T.Text) -> (T.Text, Aeson.Value)
+    fixupAttributes (k, v) = (k, Aeson.String v)
 
 parsePackage :: Opts.Parser (PackageName, PackageSpec)
 parsePackage = (,) <$> parsePackageName <*> parsePackageSpec
@@ -250,10 +251,10 @@ completePackageSpec = execStateT $ do
     whenNotSet "url_template" $
       setPackageSpecAttr
         "url_template"
-        (Aeson.String $ T.pack githubURLTemplate)
+        (Aeson.String githubURLTemplate)
 
   where
-    githubURLTemplate :: String
+    githubURLTemplate :: T.Text
     githubURLTemplate =
       "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
 
@@ -384,12 +385,13 @@ cmdAdd :: Maybe PackageName -> (PackageName, PackageSpec) -> IO ()
 cmdAdd mPackageName (PackageName str, spec) = do
 
     -- Figures out the owner and repo
-    (packageName, spec') <- flip runStateT spec $ case span (/= '/') str of
-          (owner@(_:_), '/':repo@(_:_)) -> do
+    (packageName, spec') <- flip runStateT spec $ case T.span (/= '/') str of
+          ( owner@(T.null -> False)
+            , T.uncons -> Just ('/', repo@(T.null -> False))) -> do
             whenNotSet "owner" $
-              setPackageSpecAttr "owner" (Aeson.String $ T.pack owner)
+              setPackageSpecAttr "owner" (Aeson.String owner)
             whenNotSet "repo" $ do
-                setPackageSpecAttr "repo" (Aeson.String $ T.pack repo)
+                setPackageSpecAttr "repo" (Aeson.String repo)
             pure (PackageName repo)
           _ -> pure (PackageName str)
 
@@ -420,7 +422,7 @@ cmdShow = do
     sources <- unSources <$> getSources
 
     forWithKeyM_ sources $ \key (PackageSpec spec) -> do
-      putStrLn $ "Package: " <> unPackageName key
+      T.putStrLn $ "Package: " <> unPackageName key
       forM_ (HMap.toList spec) $ \(attrName, attrValValue) -> do
         let attrValue = case attrValValue of
               Aeson.String str -> str
@@ -451,7 +453,7 @@ parseCmdUpdate =
 cmdUpdate :: Maybe (PackageName, PackageSpec) -> IO ()
 cmdUpdate = \case
     Just (packageName, packageSpec) -> do
-      putStrLn $ "Updating single package: " <> unPackageName packageName
+      T.putStrLn $ "Updating single package: " <> unPackageName packageName
       sources <- unSources <$> getSources
 
       packageSpec' <- case HMap.lookup packageName sources of
@@ -471,7 +473,7 @@ cmdUpdate = \case
 
       sources' <- forWithKeyM sources $
         \packageName packageSpec -> do
-          putStrLn $ "Package: " <> unPackageName packageName
+          T.putStrLn $ "Package: " <> unPackageName packageName
           updatePackageSpec =<< completePackageSpec packageSpec
 
       setSources $ Sources sources'
@@ -503,7 +505,7 @@ parseCmdDrop =
 cmdDrop :: PackageName -> [T.Text] -> IO ()
 cmdDrop packageName = \case
     [] -> do
-      putStrLn $ "Dropping package: " <> unPackageName packageName
+      T.putStrLn $ "Dropping package: " <> unPackageName packageName
       sources <- unSources <$> getSources
 
       when (not $ HMap.member packageName sources) $
@@ -514,7 +516,7 @@ cmdDrop packageName = \case
     attrs -> do
       putStrLn $ "Dropping attributes :" <>
         (T.unpack (T.intercalate " " attrs))
-      putStrLn $ "In package: " <> unPackageName packageName
+      T.putStrLn $ "In package: " <> unPackageName packageName
       sources <- unSources <$> getSources
 
       packageSpec <- case HMap.lookup packageName sources of
@@ -600,9 +602,9 @@ renderTemplate vals = \case
     c:str -> (c:) <$> renderTemplate vals str
     [] -> Just []
 
-abort :: String -> IO a
+abort :: T.Text -> IO a
 abort msg = do
-    putStrLn msg
+    T.putStrLn msg
     exitFailure
 
 nixPrefetchURL :: Bool -> String -> IO String
@@ -637,18 +639,18 @@ shouldUpdateNixSourcesNix content =
 warnIfOutdated :: IO ()
 warnIfOutdated = do
     tryAny (B.readFile pathNixSourcesNix) >>= \case
-      Left e -> putStrLn $ unlines
-        [ "Could not read " <> pathNixSourcesNix
-        , "Error: " <> show e
+      Left e -> T.putStrLn $ T.unlines
+        [ "Could not read " <> T.pack pathNixSourcesNix
+        , "Error: " <> tshow e
         ]
       Right content ->
         if shouldUpdateNixSourcesNix content
         then
-          putStrLn $ unlines
-            [ "WARNING: " <> pathNixSourcesNix <> " is out of date."
+          T.putStrLn $ T.unlines
+            [ "WARNING: " <> T.pack pathNixSourcesNix <> " is out of date."
             , "Please run"
             , "  niv init"
-            , "or add the following line in the " <> pathNixSourcesNix <> "  file:"
+            , "or add the following line in the " <> T.pack pathNixSourcesNix <> "  file:"
             , "  # niv: no_update"
             ]
         else pure ()
@@ -707,9 +709,9 @@ The sources file does not exist! You may need to run 'niv init'.
 |]
 
 abortSourcesIsntAMap :: IO a
-abortSourcesIsntAMap = abort $ unlines [ line1, line2 ]
+abortSourcesIsntAMap = abort $ T.unlines [ line1, line2 ]
   where
-    line1 = "Cannot use " <> pathNixSourcesJson
+    line1 = "Cannot use " <> T.pack pathNixSourcesJson
     line2 = [s|
 The sources file should be a JSON map from package name to package
 specification, e.g.:
@@ -717,9 +719,9 @@ specification, e.g.:
 |]
 
 abortAttributeIsntAMap :: IO a
-abortAttributeIsntAMap = abort $ unlines [ line1, line2 ]
+abortAttributeIsntAMap = abort $ T.unlines [ line1, line2 ]
   where
-    line1 = "Cannot use " <> pathNixSourcesJson
+    line1 = "Cannot use " <> T.pack pathNixSourcesJson
     line2 = [s|
 The package specifications in the sources file should be JSON maps from
 attribute name to attribute value, e.g.:
@@ -727,13 +729,13 @@ attribute name to attribute value, e.g.:
 |]
 
 abortSourcesIsntJSON :: IO a
-abortSourcesIsntJSON = abort $ unlines [ line1, line2 ]
+abortSourcesIsntJSON = abort $ T.unlines [ line1, line2 ]
   where
-    line1 = "Cannot use " <> pathNixSourcesJson
+    line1 = "Cannot use " <> T.pack pathNixSourcesJson
     line2 = "The sources file should be JSON."
 
 abortCannotAddPackageExists :: PackageName -> IO a
-abortCannotAddPackageExists (PackageName n) = abort $ unlines
+abortCannotAddPackageExists (PackageName n) = abort $ T.unlines
     [ "Cannot add package " <> n <> "."
     , "The package already exists. Use"
     , "  niv drop " <> n
@@ -743,7 +745,7 @@ abortCannotAddPackageExists (PackageName n) = abort $ unlines
     ]
 
 abortCannotUpdateNoSuchPackage :: PackageName -> IO a
-abortCannotUpdateNoSuchPackage (PackageName n) = abort $ unlines
+abortCannotUpdateNoSuchPackage (PackageName n) = abort $ T.unlines
     [ "Cannot update package " <> n <> "."
     , "The package doesn't exist. Use"
     , "  niv add " <> n
@@ -751,13 +753,13 @@ abortCannotUpdateNoSuchPackage (PackageName n) = abort $ unlines
     ]
 
 abortCannotDropNoSuchPackage :: PackageName -> IO a
-abortCannotDropNoSuchPackage (PackageName n) = abort $ unlines
+abortCannotDropNoSuchPackage (PackageName n) = abort $ T.unlines
     [ "Cannot drop package " <> n <> "."
     , "The package doesn't exist."
     ]
 
 abortCannotAttributesDropNoSuchPackage :: PackageName -> IO a
-abortCannotAttributesDropNoSuchPackage (PackageName n) = abort $ unlines
+abortCannotAttributesDropNoSuchPackage (PackageName n) = abort $ T.unlines
     [ "Cannot drop attributes of package " <> n <> "."
     , "The package doesn't exist."
     ]
@@ -771,3 +773,6 @@ ticket:
 
 Thanks! I'll buy you a beer.
 |]
+
+tshow :: Show a => a -> T.Text
+tshow = T.pack . show