Creating the getopt function

GetOpt.hs

@@ -3,4 +3,20 @@ module GetOpt where
 
 import GetOpt.Data
 import GetOpt.Options
-import GetOpt.Parsers
+import GetOpt.Parsers
+
+getOpt :: Parser a -> [String] -> Maybe (a, [String])
+getOpt (DefParser a) args = Just (a, args)
+getOpt p args = case runParser p args of
+                     Just (p1, args1) -> getOpt p1 args1
+                     Nothing          -> Nothing
+    where
+        runParser :: Parser a -> [String] -> Maybe (Parser a, [String])
+        runParser (OptParser opt next) (identifier:arg:args)
+            | optionMatch opt identifier = do
+                ret <- parser opt arg
+                return (fmap ret next, args)
+            | otherwise                  = do
+                (nextP, newArgs) <- runParser next (identifier:args)
+                return (OptParser opt nextP, newArgs)
+        runParser p@(DefParser _) args = Just (p, args)

GetOpt/Data.hs

@@ -10,8 +10,6 @@ data Parser a where
     DefParser :: a -> Parser a
     OptParser :: Option (a -> b) -> Parser a -> Parser b
 
--- newtype OptionParser a = OptionParser { parse :: String -> Maybe a }
-
 type OptionParser a = (String -> Maybe a)
 
 data Option a = Option {

GetOpt/Options.hs

@@ -31,4 +31,8 @@ instance Semigroup (Mod a) where
 option :: OptionParser a -> Mod a -> Parser a
 option p (Mod m) = OptParser (fmap const (m $ def p)) (DefParser ())
    where
-       def = Option "VAR" "" ' ' Nothing "No help message set."
+       def = Option "VAR" "" ' ' Nothing "No help message set."
+
+optionMatch :: Option a -> String -> Bool
+optionMatch opt [d, s] = d == '-' && s == shortName opt
+optionMatch opt (d:d1:l) = d == '-' && d1 ==  '-' && l == longName opt