Parse command-line options

mima-run/Main.hs

@@ -1,4 +1,10 @@
 module Main where
 
+import Options.Applicative
+
+import Mima.MimaRun.Options
+
 main :: IO ()
-main = putStrLn "In the beginning, there was nothing."
+main = do
+  opts <- execParser parserInfo
+  putStrLn $ "The options are: " ++ show opts

mima-run/Mima/MimaRun/Options.hs

@@ -0,0 +1,27 @@
+module Mima.MimaRun.Options
+  ( Options(..)
+  , parserInfo
+  ) where
+
+import Options.Applicative
+
+data Options = Options
+  { inputFile :: FilePath
+  , steps :: Maybe Integer
+  } deriving (Show)
+
+parser :: Parser Options
+parser = Options
+  <$> strOption
+      (  help "The .mima file to use"
+      <> metavar "INPUTFILE"
+      )
+  <*> (optional . option auto)
+      (  short 'n'
+      <> long "steps"
+      <> help "Maximum number of steps to execute"
+      <> metavar "STEPS"
+      )
+
+parserInfo :: ParserInfo Options
+parserInfo = info (parser <**> helper) (failureCode 1)