Add the PDF generator snippets

app/Main.hs

@@ -16,10 +16,11 @@ import Graphics.Fountainhead.Parser
     )
 import Graphics.Fountainhead.TrueType (FontDirectory(..), TableDirectory(..))
 import System.Environment (getArgs)
+import System.Exit (exitWith)
+import GHC.IO.Exception (ExitCode(..))
 
-fontMain :: IO ()
-fontMain = do
-    fontFile <- head <$> getArgs
+fontMain :: FilePath -> IO ()
+fontMain fontFile = do
     ttfContents <- ByteString.readFile fontFile
 
     let initialState = Megaparsec.State
@@ -43,4 +44,9 @@ fontMain = do
         Right x -> print x
 
 main :: IO ()
-main = fontMain
+main = do
+    programArguments <- getArgs
+    case programArguments of
+        [fontFile] -> fontMain fontFile
+        _ -> putStrLn "The program expects exactly one argument, the font file path."
+            >> exitWith (ExitFailure 2)