Make input directory absolute and check it exists

src/Arguments.hs

@@ -6,6 +6,8 @@ module Arguments (
 
 import Data.Monoid ((<>))
 import Options.Applicative
+import System.Directory (doesDirectoryExist, makeAbsolute)
+import System.Exit (die)
 import System.FilePath.Posix (dropTrailingPathSeparator, isValid)
 
 data Arguments = Arguments {
@@ -39,8 +41,11 @@ directory = eitherReader $ \path ->
     else Left "This string doesn't represent a valid path"
 
 configuration :: IO Arguments
-configuration =
-  execParser $
-    info (arguments <**> helper)
-      ( fullDesc
-      )
+configuration = do
+  inputArguments <- execParser $ info (arguments <**> helper) fullDesc
+  directoryExists <- doesDirectoryExist $ sourceDir inputArguments
+  if directoryExists
+    then do
+      absolutePath <- makeAbsolute $ sourceDir inputArguments
+      return $ inputArguments { sourceDir = absolutePath }
+    else die "INPUT_DIR doesn't exist"