option processing

Options.hs

@@ -0,0 +1,25 @@
+module Options where
+    
+import System.Console.GetOpt
+import Data.Maybe ( fromMaybe )
+    
+data Flag = File String | Version deriving Show
+    
+options :: [OptDescr Flag]
+options = [
+           Option ['f']     ["file"] (OptArg inp "FILE") "ledger file, or - to read stdin"
+          , Option ['v'] ["version"] (NoArg Version) "show version number"
+          ]
+
+inp :: Maybe String -> Flag
+inp  = File . fromMaybe "stdin"
+    
+getOptions :: [String] -> IO ([Flag], [String])
+getOptions argv =
+    case getOpt Permute options argv of
+      (o,n,[]  ) -> return (o,n)
+      (_,_,errs) -> ioError (userError (concat errs ++ usageInfo header options))
+        where header = "Usage: hledger [OPTIONS]"
+
+get_content :: Flag -> Maybe String
+get_content (File s) = Just s

hledger.hs

@@ -1,3 +1,4 @@
+#!/usr/bin/runhaskell
 -- hledger - ledger-compatible money management utilities
 -- GPLv3, (c) Simon Michael & contributors, 
 -- ledger is at http://newartisans.com/ledger.html
@@ -104,6 +105,7 @@ import Test.QuickCheck
 import Test.HUnit
 
 --import TildeExpand -- confuses my ghc 6.7
+import System (getArgs)
 import System.Directory (getHomeDirectory)
 import System.Environment (getEnv)
 import Control.Exception (assert)
@@ -112,6 +114,8 @@ import qualified Text.ParserCombinators.Parsec.Token as P
 import Text.ParserCombinators.Parsec.Language
 import Text.Printf
 
+import Options
+
 -- sample data
 
 sample_entry = "\
@@ -454,4 +458,10 @@ register = do
     Left err -> do putStr "ledger parse error at "; print err
     Right l  -> putStr $ showLedger l
 
-main = do register
+main = do
+  (opts, args) <- getArgs >>= getOptions
+  putStr "options: "; print opts
+  putStr "arguments: "; print args
+  if "reg" `elem` args
+     then register
+     else return ()