Add command line arguments (L-system and number of iterations)

app/Main.hs

@@ -1,11 +1,55 @@
 module Main where
 
 import Graphics.Gloss
+import Options.Applicative
+import Data.Semigroup ((<>))
+import Data.List
 
 import Lib
 import Examples
 
+data Options = Options
+  { optionLSystem :: LSystem Char
+  , optionIterations :: Integer
+  }
+
+selectLSystem :: [LSystem a] -> String -> Either String (LSystem a)
+selectLSystem ls s = case find (\x -> name x == s) ls of
+  Just x -> Right x
+  Nothing -> Left $ "Cannot find L-system \"" ++ s ++ "\""
+
+lsystem :: Parser (LSystem Char)
+lsystem = argument (eitherReader (selectLSystem lsystems))
+  (metavar "LSYSTEM"
+   <> help "L-system to generate"
+   <> showDefaultWith name
+   <> value penroseP3
+   <> completeWith (map name lsystems)
+   <> completer (listCompleter (map name lsystems)))
+
+iterations :: Parser Integer
+iterations = option auto
+  (long "iterations"
+   <> short 'n'
+   <> help "Number of iterations"
+   <> showDefault
+   <> value 5
+   <> metavar "N")
+
+options :: Parser Options
+options = Options <$> lsystem <*> iterations
+
+opts :: ParserInfo Options
+opts = info (options <**> helper)
+  ( fullDesc
+  <> progDesc "Generate and draw an L-system"
+  <> header "lsystems -- Generate L-systems")
+
+createDisplay :: (Eq a, Integral p) => p -> LSystem a -> IO ()
+createDisplay n ls = display (InWindow "L-System" (200, 200) (10, 10)) black (color white pic)
+  where pic = drawLSystem $ iterateLSystem n ls
+
 main :: IO ()
-main =
-  display (InWindow "L-System" (200, 200) (10, 10)) black (color white pic)
-  where pic = drawLSystem $ iterateLSystem 6 penroseP3
+main = do
+  Options ls n <- execParser opts
+  createDisplay n ls