Upd: Nillable cenvenience stuff

ghc-802.yaml

@@ -1,3 +1,7 @@
+nix:
+  packages:
+    - zlib
+
 resolver: lts-9.21
 
 packages:

ghc-822.yaml

@@ -1 +1,5 @@
+nix:
+  packages:
+    - zlib
+
 resolver: lts-11.22

ghc-844.yaml

@@ -1,3 +1,7 @@
+nix:
+  packages:
+    - zlib
+
 resolver: lts-12.16
 extra-deps:
 - dom-parser-3.1.0

src/Text/XML/Nillable.hs

@@ -1,23 +1,33 @@
+{-# LANGUAGE MonoLocalBinds    #-}
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE MonoLocalBinds #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 
-module Text.XML.Nillable
-where
+module Text.XML.Nillable where
 
-import Control.DeepSeq
-import Text.XML.DOM.Parser
-import Text.XML.Writer
-import Text.XML.ParentAttributes
+import           Control.DeepSeq
+import           Control.Lens
+import           Text.XML.DOM.Parser
+import           Text.XML.ParentAttributes
+import           Text.XML.Writer
 
 -- | Type that can have explicit null value
 --
 -- Null value is indicated by "nil"="true" attribute.
 newtype Nillable a = Nillable (Maybe a)
-  deriving (Eq, Show, Ord, Read, NFData, ToXML)
+  deriving
+    ( Eq, Show, Ord, Read, NFData, ToXML
+    , Functor, Applicative, Monad, Foldable, Traversable)
+
+_Nillable :: Prism' (Nillable a) a
+_Nillable = coerced . _Just
+
+nNill :: Nillable a
+nNill = Nillable Nothing
+
+nJust :: a -> Nillable a
+nJust = Nillable . Just
 
 instance ToXmlParentAttributes a => ToXmlParentAttributes (Nillable a) where
-  toXmlParentAttributes (Nillable Nothing) = 
+  toXmlParentAttributes (Nillable Nothing) =
     [("{http://www.w3.org/2001/XMLSchema-instance}nil", "true")]
   toXmlParentAttributes (Nillable (Just a)) = toXmlParentAttributes a
 
@@ -28,4 +38,4 @@ instance FromDom a => FromDom (Nillable a) where
       Right
     case nil of
       Just "true" -> return (Nillable Nothing)
-      _ -> Nillable . Just <$> fromDom
+      _           -> Nillable . Just <$> fromDom

stack.yaml

@@ -1,3 +1,7 @@
+nix:
+  packages:
+    - zlib
+
 resolver: lts-10.0
 extra-deps:
 - dom-parser-3.0.0

xml-isogen.cabal

@@ -53,7 +53,9 @@ library
 
   default-language:    Haskell2010
   default-extensions:  CPP
+                     , DeriveTraversable
                      , FlexibleInstances
+                     , GeneralizedNewtypeDeriving
                      , LambdaCase
                      , TemplateHaskell
                      , TupleSections