Add support for nothing

data/dconf.settings

@@ -319,3 +319,10 @@ recently-installed-apps=['RollerCoaster Tycoon 3 Platinum!.desktop', 'RollerCoas
 
 [org/gnome/evolution-data-server/calendar/list-of-equal]
 reminders-snoozed=['=']
+
+[org/gnome/Tetravex]
+saved-game=@m(yyda(yyyyyyyy)ua(yyyyu)) nothing
+
+[org/gnome/evince]
+document-directory=@ms nothing
+pictures-directory=@ms nothing

output/dconf.nix

@@ -400,5 +400,14 @@ with lib.hm.gvariant;
       reminders-snoozed = [ "=" ];
     };
 
+    "org/gnome/Tetravex" = {
+      saved-game = mkNothing "(yyda(yyyyyyyy)ua(yyyyu))";
+    };
+
+    "org/gnome/evince" = {
+      document-directory = mkNothing "s";
+      pictures-directory = mkNothing "s";
+    };
+
   };
 }

src/DConf.hs

@@ -47,6 +47,9 @@ sepOneEndBy p sep =
 vBool :: Parsec Text () Value
 vBool = B False <$ string "false" <|> B True <$ string "true"
 
+vNothing :: Parsec Text () Value
+vNothing = No <$ string "nothing"
+
 vDouble :: Parsec Text () Value
 vDouble = try $ do
   s <- option "" $ string "-"
@@ -120,7 +123,7 @@ baseValue = choice
 
 value :: Parsec Text () Value
 value = choice
-  [vTyped, vDictDictEntry, vList, vJson, baseValue, vCast, vTuple, vVariant]
+  [vTyped, vDictDictEntry, vList, vJson, baseValue, vCast, vNothing, vTuple, vVariant]
 
 vVariant :: Parsec Text () Value
 vVariant = fmap V $ bracket "<" ">" value

src/DConf/Data.hs

@@ -44,6 +44,7 @@ castName TyObjectpath = "objectpath"
 
 data Value = S Text         -- String
            | B Bool         -- Bool
+           | No             -- Nothing case of Maybe
            | I Int          -- Int
            | C Ty Value     -- Cast
            | D Double       -- Double

src/Nix.hs

@@ -91,6 +91,7 @@ renderValue raw = Nix $ renderValue' raw <> ";"
 
   renderValue' (S   v) = renderString v
   renderValue' (B   v) = T.toLower . T.pack $ show v
+  renderValue' (No   ) = error "Standalone nothing not supported"
   renderValue' (I   v) = T.pack $ show v
   renderValue' (D   v) = T.pack $ show v
   renderValue' (C ty v) =
@@ -102,6 +103,7 @@ renderValue raw = Nix $ renderValue' raw <> ";"
   renderValue' (T  xs) = "mkTuple " <> renderList xs
   -- In home-manager, @mkValue []@ emits @\@as []@
   renderValue' (Ty "as" (L [])) = renderList []
+  renderValue' (Ty ('m':t) No) = "mkNothing " <> T.pack (show t)
   -- In home-manager, arrays are always typed when using @mkArray@.
   renderValue' (Ty ('a':t) (L v)) = "mkArray " <> T.pack (show t) <> " " <> renderList v
   -- TODO: add mkTyped to h-m