Add an option for dumping a single table

src/Main.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE RecordWildCards #-}
 module Main
     ( main
     ) where
@@ -5,49 +6,49 @@ module Main
 import qualified Data.Text.Lazy.Builder as Text.Builder
 import qualified Data.Text.Lazy.IO as Text.Lazy
 import Graphics.Fountainhead (dumpFontFile)
-import System.Exit (exitWith)
-import GHC.IO.Exception (ExitCode(..))
 import Options.Applicative
-    ( Parser
-    , ParserInfo(..)
+    ( ParserInfo(..)
     , (<**>)
     , argument
-    , command
     , execParser
+    , header
+    , help
     , helper
     , info
+    , long
     , fullDesc
     , metavar
+    , optional
     , progDesc
+    , short
     , str
-    , subparser
+    , strOption
     )
 
-data Operation
-    = Dump
-    | Afm
-    deriving (Eq, Show)
-
-data Options = Options Operation FilePath
-    deriving (Eq, Show)
+data Options = Options
+    { tableName :: Maybe String
+    , fontFile :: FilePath
+    } deriving (Eq, Show)
 
 operationOptions :: ParserInfo Options
-operationOptions = info (options <**> helper) fullDesc
+operationOptions = info (options <**> helper)
+    $ fullDesc
+    <> progDesc "Dumping the contents of a TrueType Font file."
+    <> header "fountainhead - font parser"
   where
     options = Options
-        <$> commands
+        <$> tableNameArgument
         <*> argument str (metavar "FONTFILE")
-    commands = subparser
-        $ command "dump" (info (pure Dump) (progDesc "Dumping the contents of a TrueType Font file."))
-        <> command "afm" (info (pure Afm) (progDesc "Generating Adobe Font Metrics files for TrueType fonts."))
+    tableNameArgument = optional $ strOption
+        $ long "table"
+        <> short 't'
+        <> metavar "tablename"
+        <> help "Dump only the specified table. Otherwise dump all tables"
 
 main :: IO ()
 main = execParser operationOptions >>= handleArguments
   where
-    handleArguments (Options Dump fontFile)
+    handleArguments Options{..}
         = putStrLn ("Dumping File:" <> fontFile <> "\n\n")
-        >> dumpFontFile fontFile
+        >> dumpFontFile fontFile tableName
         >>= either print (Text.Lazy.putStrLn . Text.Builder.toLazyText)
-    handleArguments (Options Afm _)
-        = putStrLn "The program expects exactly one argument, the font file path."
-        >> exitWith (ExitFailure 2)