Give precedence to custom reader in option builder (#19).

Options/Applicative/Builder.hs

@@ -365,11 +365,11 @@ nullOption m = mkParser d g rdr
 
 -- | Builder for an option taking a 'String' argument.
 strOption :: Mod OptionFields String -> Parser String
-strOption m = nullOption $ m & reader str
+strOption m = nullOption $ reader str & m
 
 -- | Builder for an option using the 'auto' reader.
 option :: Read a => Mod OptionFields a -> Parser a
-option m = nullOption $ m & reader auto
+option m = nullOption $ reader auto & m
 
 -- | Modifier for 'ParserInfo'.
 newtype InfoMod a = InfoMod

tests/Tests.hs

@@ -191,5 +191,17 @@ case_bind_usage = do
     Right val ->
       assertFailure $ "unexpected result " ++ show val
 
+case_issue_19 :: Assertion
+case_issue_19 = do
+  let p = option
+        ( short 'x'
+        & reader (Just . str)
+        & value Nothing )
+      i = info (p <**> helper) idm
+      result = run i ["-x", "foo"]
+  case result of
+    Left _ -> assertFailure "unexpected parse error"
+    Right r -> Just "foo" @=? r
+
 main :: IO ()
 main = $(defaultMainGenerator)