Some major changes to the structure of the language.

Added structures and unions to better define the layout and model
overlapping concerns.

renamed objtype -> type and object -> instance.

added reserved statements for types.

9 files changed, 354 insertions, 91 deletions

diff --git a/goal.fiddle b/goal.fiddle
index b87f0e9..b59acb4 100644
--- a/goal.fiddle
+++ b/goal.fiddle
@@ -1,6 +1,7 @@
 option endian little;
 
 // package for the GPIO system.
+
 package gpio {
 
   location gpio_a_base = 0x4800_0000;
@@ -16,9 +17,9 @@ package gpio {
   /**
    * Structure of the GPIO port on an stm32l432
    */
-  objtype gpio_t : {
+  type gpio_t : struct {
     assert_pos(0);
-    reg (32) : {
+    reg (32) : struct {
       /** The mode for each pin. */
       mode_r : enum(2) {
         /** The GPIO pin is used for input. */
@@ -44,7 +45,7 @@ package gpio {
      * The output type.
      */
     assert_pos(0x04);
-    reg ocfg_reg(32) : {
+    reg ocfg_reg(32) : struct {
       otype_r : enum(1) {
         /**
          * The GPIO pin is capable of sinking to ground (for LOW) or providing
@@ -66,7 +67,7 @@ package gpio {
      * Sets the speed of the provided GPIO pin.
      */
     assert_pos(0x08);
-    reg (32) : {
+    reg (32) : struct {
       ospeed_r : enum(2) {
         low = 0,
         medium = 1,
@@ -79,16 +80,26 @@ package gpio {
      * Pullup/Pulldown type
      */
     assert_pos(0x0c);
-    wo reg (32) : {
-      pupd_r : enum(2) {
-        none = 0b0,
-        // Compiles to Gpio::PupdR::PullUp
-        pull_up = 0b1,
-        // Compiles to Gpio::PupdR::PullDown
-        pull_down = 0b10,
-        // Not used, but has to be included to fill out the enum.
-        reserved = 0b11,
-      } [16];
+    wo reg (32) : struct {
+      union {
+        pupd_r : enum(2) {
+          none = 0b0,
+          // Compiles to Gpio::PupdR::PullUp
+          pull_up = 0b1,
+          // Compiles to Gpio::PupdR::PullDown
+          pull_down = 0b10,
+          // Not used, but has to be included to fill out the enum.
+          reserved = 0b11,
+        } [16];
+
+        struct {
+          alternate : enum(1) {
+            enabled = 0,
+            disabled = 1,
+          } [16];
+          reserved(16);
+        };
+      };
     };
 
     /**
@@ -97,11 +108,26 @@ package gpio {
      * Reading form the provided pin will yield high if the pin is on, or low if
      * the pin is low.
      */
-    assert_pos(0x10);
-    ro reg (32) : {
-      id_r : data_t[16];
-      reserved(16);
+    union {
+      assert_pos(0x10);
+      ro reg (32) : struct {
+        id_r : data_t[16];
+        reserved(16);
+      };
+
+      // Additinoal values .
+      assert_pos(0x10);
+      struct {
+        assert_pos(0x10);
+        wo reg alt_r1(16);
+
+        assert_pos(0x12);
+        wo reg alt_r2(8);
+        reserved(8);
+      };
     };
+    assert_pos(0x14);
+
 
     /**
      * Output data register.
@@ -109,8 +135,18 @@ package gpio {
      * Writing to this register sets the appropriate register to low/high.
      */
     assert_pos(0x14);
-    wo reg (32) : {
-      rw od_r : data_t[16];
+    wo reg (32) : struct {
+      union {
+        rw od_r : data_t[16];
+
+        struct {
+          rw osp_v : (15);
+          // Without the reserved bit, the compiler will complain about jagged
+          // unions. 
+          reserved(1);
+        };
+      };
+
       reserved(16);
     };
 
@@ -118,7 +154,7 @@ package gpio {
      * The GPIO port bit set/reset register.
      */
     assert_pos(0x18);
-    reg bsr_r(32) : {
+    reg bsr_r(32) : struct {
       /**
        * Sets the pins associated with the bits. Like od_r, but can be used to
        * turn on multiple pins at once.
@@ -132,7 +168,7 @@ package gpio {
     };
 
     assert_pos(0x1c);
-    reg(32) : {
+    reg(32) : struct {
       lock : enum(1) {
         unlocked = 0,
         locked = 1,
@@ -148,7 +184,7 @@ package gpio {
      * Each nybble refers to a pin.
      */
     assert_pos(0x20);
-    reg(64) : {
+    reg(64) : struct {
       afn : (4)[16];
     };
 
@@ -156,7 +192,7 @@ package gpio {
      * The bit reset register.
      */
     assert_pos(0x28);
-    reg(32) : {
+    reg(32) : struct {
       wo br_r : (16);
       reserved (16);
     };
@@ -164,13 +200,13 @@ package gpio {
     /**
      * Analog switch control for the pin.
      */
-    reg(32) : {
+    reg(32) : struct {
       asc_r : (16);
       reserved (16);
     };
   };
 
-  object gpio_a at gpio_a_base : gpio_t;
-  object gpio_b at gpio_b_base : gpio_t;
-  object gpio_c at gpio_c_base : gpio_t;
+  instance gpio_a at gpio_a_base : gpio_t;
+  instance gpio_b at gpio_b_base : gpio_t;
+  instance gpio_c at gpio_c_base : gpio_t;
 };
diff --git a/package.yaml b/package.yaml
index f2394a7..56f6ffd 100644
--- a/package.yaml
+++ b/package.yaml
@@ -35,3 +35,4 @@ dependencies:
   - data-default
   - transformers
   - containers
+  - optparse-applicative
diff --git a/src/Language/Fiddle/Ast.hs b/src/Language/Fiddle/Ast.hs
index d440a44..8352975 100644
--- a/src/Language/Fiddle/Ast.hs
+++ b/src/Language/Fiddle/Ast.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE DefaultSignatures #-}
 {-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE DeriveGeneric #-}
@@ -5,7 +6,6 @@
 {-# LANGUAGE IncoherentInstances #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE UndecidableInstances #-}
-{-# LANGUAGE ConstraintKinds #-}
 
 module Language.Fiddle.Ast where
 
@@ -18,6 +18,8 @@ import Data.Typeable
 import GHC.Generics
 import GHC.TypeLits
 
+-- The type of a number at each stage in compilation. Numbers should be parsed
+-- in Stage2.
 type family NumberType (a :: Stage) where
   NumberType Stage1 = Text
   NumberType Stage2 = Integer
@@ -88,7 +90,7 @@ data FiddleDecl (stage :: Stage) (f :: Type -> Type) a where
   deriving (Generic, Annotated, Alter, Typeable)
 
 data ObjTypeBody (stage :: Stage) (f :: Type -> Type) a where
-  ObjTypeBody :: [ObjTypeDecl stage f a] -> a -> ObjTypeBody stage f a
+  ObjTypeBody :: BodyType f a -> [ObjTypeDecl stage f a] -> a -> ObjTypeBody stage f a
   deriving (Generic, Annotated, Alter, Typeable)
 
 data ObjType stage f a where
@@ -119,6 +121,14 @@ data ObjTypeDecl stage f a where
     Maybe (RegisterBody stage f a) ->
     a ->
     ObjTypeDecl stage f a
+  {- reserved(n); -}
+  ReservedDecl :: Expression stage f a -> a -> ObjTypeDecl stage f a
+  {- <struct|union> { subfields } <name>; -}
+  TypeSubStructure ::
+    f (ObjTypeBody stage f a) ->
+    Maybe (Identifier f a) ->
+    a ->
+    ObjTypeDecl stage f a
   deriving (Typeable)
 
 data Modifier f a where
@@ -134,8 +144,13 @@ data DeferredRegisterBody stage f a where
     DeferredRegisterBody stage f a
   deriving (Generic, Annotated, Alter, Typeable)
 
+data BodyType (f :: Type -> Type) a where
+  Union :: a -> BodyType f a
+  Struct :: a -> BodyType f a
+  deriving (Generic, Annotated, Alter, Typeable)
+
 data RegisterBody stage f a where
-  RegisterBody :: f (DeferredRegisterBody stage f a) -> a -> RegisterBody stage f a
+  RegisterBody :: BodyType f a -> f (DeferredRegisterBody stage f a) -> a -> RegisterBody stage f a
   deriving (Generic, Annotated, Alter, Typeable)
 
 data RegisterBitsDecl stage f a where
@@ -148,6 +163,11 @@ data RegisterBitsDecl stage f a where
     RegisterBitsTypeRef stage f a ->
     a ->
     RegisterBitsDecl stage f a
+  BitsSubStructure ::
+    RegisterBody stage f a ->
+    Maybe (Identifier f a) ->
+    a ->
+    RegisterBitsDecl stage f a
   deriving (Generic, Annotated, Alter, Typeable)
 
 data RegisterBitsTypeRef stage f a where
@@ -195,6 +215,15 @@ instance Alter (ObjTypeDecl stage) where
         <*> alter ffn fn expr
         <*> mapM (alter ffn fn) mBody
         <*> fn a
+    (TypeSubStructure mBody mIdent a) ->
+      TypeSubStructure
+        <$> (ffn =<< mapM (alter ffn fn) mBody)
+        <*> mapM (alter ffn fn) mIdent
+        <*> fn a
+    (ReservedDecl expr a) ->
+      ReservedDecl
+        <$> alter ffn fn expr
+        <*> fn a
 
 instance Annotated (ObjTypeDecl stage) where
   annot = \case
diff --git a/src/Language/Fiddle/Compiler/Stage1.hs b/src/Language/Fiddle/Compiler/Stage1.hs
index 3a97757..25ee66b 100644
--- a/src/Language/Fiddle/Compiler/Stage1.hs
+++ b/src/Language/Fiddle/Compiler/Stage1.hs
@@ -123,11 +123,20 @@ enumConstantToStage2 path = \case
   EnumConstantReserved e a -> EnumConstantReserved <$> toStage2Expr e <*> pure a
 
 objTypeBodyToStage2 :: Path -> ObjTypeBody Stage1 I Annot -> M Annot (ObjTypeBody Stage2 I Annot)
-objTypeBodyToStage2 path (ObjTypeBody decls annot) = ObjTypeBody <$> mapM (objTypeDeclToStage2 path) decls <*> pure annot
+objTypeBodyToStage2 path (ObjTypeBody bodyType decls annot) =
+  ObjTypeBody bodyType <$> mapM (objTypeDeclToStage2 path) decls <*> pure annot
 
 objTypeDeclToStage2 :: Path -> ObjTypeDecl Stage1 I Annot -> M Annot (ObjTypeDecl Stage2 I Annot)
 objTypeDeclToStage2 path = \case
   (AssertPosStatement expr annot) -> AssertPosStatement <$> toStage2Expr expr <*> pure annot
+  (TypeSubStructure (Identity deferredBody) maybeIdent annot) ->
+    let path' = maybe path (`pushId` path) maybeIdent
+     in TypeSubStructure . Identity
+          <$> objTypeBodyToStage2 path' deferredBody
+          <*> pure maybeIdent
+          <*> pure annot
+  (ReservedDecl expr a) ->
+    ReservedDecl <$> toStage2Expr expr <*> pure a
   (RegisterDecl maybeModifier maybeIdentifier expression maybeBody annot) ->
     let path' = maybe path (`pushId` path) maybeIdentifier
      in RegisterDecl
@@ -138,8 +147,8 @@ objTypeDeclToStage2 path = \case
           <*> pure annot
 
 registerBodyToStage2 :: Path -> RegisterBody Stage1 I Annot -> M Annot (RegisterBody Stage2 I Annot)
-registerBodyToStage2 path (RegisterBody (Identity (DeferredRegisterBody registerBitsDecl a1)) a2) =
-  RegisterBody . Identity
+registerBodyToStage2 path (RegisterBody bodyType (Identity (DeferredRegisterBody registerBitsDecl a1)) a2) =
+  RegisterBody bodyType . Identity
     <$> ( DeferredRegisterBody
             <$> mapM (registerBitsDeclToStage2 path) registerBitsDecl
             <*> pure a1
@@ -149,6 +158,9 @@ registerBodyToStage2 path (RegisterBody (Identity (DeferredRegisterBody register
 registerBitsDeclToStage2 :: Path -> RegisterBitsDecl Stage1 I Annot -> M Annot (RegisterBitsDecl Stage2 I Annot)
 registerBitsDeclToStage2 path = \case
   ReservedBits expr a -> ReservedBits <$> toStage2Expr expr <*> pure a
+  BitsSubStructure registerBody maybeIdent annot ->
+    let path' = maybe path (`pushId` path) maybeIdent
+     in BitsSubStructure <$> registerBodyToStage2 path' registerBody <*> pure maybeIdent <*> pure annot
   DefinedBits maybeModifier identifier registerBitsTyperef annot ->
     let path' = pushId identifier path
      in ( DefinedBits
diff --git a/src/Language/Fiddle/Compiler/Stage2.hs b/src/Language/Fiddle/Compiler/Stage2.hs
index baa61e3..727f153 100644
--- a/src/Language/Fiddle/Compiler/Stage2.hs
+++ b/src/Language/Fiddle/Compiler/Stage2.hs
@@ -117,8 +117,8 @@ getTypeSize (EnumBitType expr (Identity (EnumBody constants _)) ann) = do
         [ Diagnostic
             Warning
             ( printf
-                "Missing enum constants %s. Please fully pack a small enum.\
-                \ Use 'reserved' if needed."
+                "Missing enum constants %s. Small enums should be fully \
+                \ populated. Use 'reserved' if needed."
                 (intercalate ", " (map show missing))
             )
             (unCommented ann)
@@ -136,7 +136,7 @@ fiddleDeclToStage3 = \case
     addTypeSize id typeSize
     BitsDecl id <$> bitTypeToStage3 typ <*> pure a
   ObjTypeDecl ident body a ->
-    ObjTypeDecl ident <$> mapM objTypeBodyToStage3 body <*> pure a
+    ObjTypeDecl ident <$> mapM (\bt -> fst <$> objTypeBodyToStage3 bt 0) body <*> pure a
   ObjectDecl ident expr typ a ->
     ObjectDecl ident (expressionToStage3 expr) <$> objTypeToStage3 typ <*> pure a
 
@@ -152,7 +152,11 @@ objTypeToStage3 = \case
 registerBodyToStage3 ::
   RegisterBody Stage2 I Annot ->
   Compile Stage3State (RegisterBody Stage3 I Annot, Word32)
-registerBodyToStage3 (RegisterBody (Identity deferredRegisterBody) a') =
+registerBodyToStage3 (RegisterBody bodyType (Identity deferredRegisterBody) a') = do
+  let isUnion = case bodyType of
+        Union {} -> True
+        _ -> False
+
   case deferredRegisterBody of
     DeferredRegisterBody decls a -> do
       (cur, returned) <-
@@ -160,17 +164,79 @@ registerBodyToStage3 (RegisterBody (Identity deferredRegisterBody) a') =
           ( \(cursor, returned) decl ->
               case decl of
                 ReservedBits expr a -> do
-                  size <- exprToSize expr
+                  size <- fromIntegral <$> exprToSize expr
                   let s3 = ReservedBits (expressionToStage3 expr) a
-                  return (cursor + fromIntegral size, s3 : returned)
+                  if isUnion
+                    then checkUnion cursor size (s3 : returned) a
+                    else
+                      return (cursor + size, s3 : returned)
+                BitsSubStructure registerBody maybeIdent annot -> do
+                  checkBitsSubStructure registerBody maybeIdent annot
+
+                  (newBody, subsize) <- registerBodyToStage3 registerBody
+                  let s3 = BitsSubStructure newBody maybeIdent annot
+
+                  if isUnion
+                    then checkUnion cursor subsize (s3 : returned) a
+                    else
+                      return (cursor + subsize, s3 : returned)
                 DefinedBits modifier identifier typeref a -> do
                   (s3TypeRef, size) <- registerBitsTypeRefToStage3 typeref
-                  return (cursor + size, DefinedBits modifier identifier s3TypeRef a : returned)
+                  let s3 = DefinedBits modifier identifier s3TypeRef a
+
+                  if isUnion
+                    then checkUnion cursor size (s3 : returned) a
+                    else
+                      return (cursor + size, s3 : returned)
           )
           (0, [])
           decls
 
-      return (RegisterBody (Identity (DeferredRegisterBody (reverse returned) a)) a', cur)
+      return (RegisterBody bodyType (Identity (DeferredRegisterBody (reverse returned) a)) a', cur)
+  where
+    checkBitsSubStructure
+      (RegisterBody bodyType (Identity (DeferredRegisterBody decls _)) _)
+      maybeIdent
+      annot =
+        let emitWarning s = tell [Diagnostic Warning s (unCommented annot)]
+         in case () of
+              ()
+                | [_] <- decls,
+                  (Union {}) <- bodyType ->
+                    emitWarning "Union with a single field. Should this be a struct?"
+              ()
+                | [_] <- decls,
+                  (Struct {}) <- bodyType,
+                  Nothing <- maybeIdent ->
+                    emitWarning "Anonymous sub-struct with single field is superfluous."
+              ()
+                | [] <- decls ->
+                    emitWarning
+                      ( printf
+                          "Empty sub-%s is superfluous."
+                          ( case bodyType of
+                              Union {} -> "union"
+                              Struct {} -> "struct"
+                          )
+                      )
+              _ -> return ()
+
+checkUnion :: Word32 -> Word32 -> b -> Commented SourceSpan -> Compile Stage3State (Word32, b)
+checkUnion cursor subsize ret a = do
+  when (cursor /= 0 && subsize /= cursor) $ do
+    tell
+      [ Diagnostic
+          Warning
+          ( printf
+              "Jagged union found. Found size %d, expected %d.\n \
+              \ Please wrap smaller fields in a struct with padding so all \
+              \ fields are the same size?"
+              subsize
+              cursor
+          )
+          (unCommented a)
+      ]
+  return (max cursor subsize, ret)
 
 registerBitsTypeRefToStage3 ::
   RegisterBitsTypeRef Stage2 I Annot ->
@@ -191,8 +257,11 @@ registerBitsTypeRefToStage3 = \case
       <$> exprToSize expr
 
 objTypeBodyToStage3 ::
-  ObjTypeBody Stage2 I Annot -> Compile Stage3State (ObjTypeBody Stage3 I Annot)
-objTypeBodyToStage3 (ObjTypeBody decls a) = do
+  ObjTypeBody Stage2 I Annot -> Word32 -> Compile Stage3State (ObjTypeBody Stage3 I Annot, Word32)
+objTypeBodyToStage3 (ObjTypeBody bodyType decls a) startOff = do
+  let isUnion = case bodyType of
+        Union {} -> True
+        _ -> False
   (cur, returned) <-
     foldlM
       ( \(cursor, returned) decl ->
@@ -209,7 +278,7 @@ objTypeBodyToStage3 (ObjTypeBody decls a) = do
                       s3RegisterBody
                       a
 
-              declaredSizeBits <- exprToSize expr
+              declaredSizeBits <- fromIntegral <$> exprToSize expr
 
               when ((declaredSizeBits `mod` 8) /= 0) $
                 tell
@@ -222,45 +291,108 @@ objTypeBodyToStage3 (ObjTypeBody decls a) = do
               forM_ mCalculatedSize $ \(fromIntegral -> calculatedSize) ->
                 unless (calculatedSize == declaredSizeBits) $
                   let helpful =
-                        if calculatedSize < declaredSizeBits then
-                          printf "\nPerhaps you should add 'reserved(%d)' to the end of your register declaration?"
-                            (declaredSizeBits - calculatedSize)
-                            else ""
-                  in
-
-                  tell
-                    [ Diagnostic
-                        Error
-                        ( printf
-                            "Calculated size %d does not match declared size %d.%s"
-                            calculatedSize
-                            declaredSizeBits
-                            helpful
-                        )
-                        (unCommented a)
-                    ]
-
-              return (cursor + declaredSizeBits `div` 8, s3 : returned)
+                        if calculatedSize < declaredSizeBits
+                          then
+                            printf
+                              "\nPerhaps you should add 'reserved(%d)' to the end of your register declaration?"
+                              (declaredSizeBits - calculatedSize)
+                          else ""
+                   in tell
+                        [ Diagnostic
+                            Error
+                            ( printf
+                                "Calculated size %d does not match declared size %d.%s"
+                                calculatedSize
+                                declaredSizeBits
+                                helpful
+                            )
+                            (unCommented a)
+                        ]
+
+              if isUnion
+                then
+                  checkUnion cursor (declaredSizeBits `div` 8) (s3 : returned) a
+                else
+                  return (cursor + declaredSizeBits `div` 8, s3 : returned)
+            TypeSubStructure (Identity subBody) maybeIdent annot -> do
+              (newBody, size) <-
+                objTypeBodyToStage3
+                  subBody
+                  ( if isUnion then startOff else cursor
+                  )
+              let s3 = TypeSubStructure (Identity newBody) maybeIdent annot
+
+              checkTypesSubStructure subBody maybeIdent annot
+              if isUnion
+                then
+                  checkUnion cursor size (s3 : returned) a
+                else
+                  return (cursor + size, s3 : returned)
+            ReservedDecl expr annot -> do
+              size' <- fromIntegral <$> exprToSize expr
+              when ((size' `mod` 8) /= 0) $
+                tell
+                  [ Diagnostic
+                      Error
+                      "Can only reserve a multiple of 8 bits in this context."
+                      (unCommented a)
+                  ]
+              let size = size' `div` 8
+              let s3 = ReservedDecl (expressionToStage3 expr) annot
+              if isUnion
+                then
+                  checkUnion cursor size (s3 : returned) a
+                else
+                  return (cursor + size, s3 : returned)
             AssertPosStatement expr a -> do
-              declaredPos <- exprToSize expr
-              when (cursor /= declaredPos) $ do
+              declaredPos <- fromIntegral <$> exprToSize expr
+
+              let expectedPos = if isUnion then startOff else cursor + startOff
+
+              when (expectedPos /= declaredPos) $ do
                 tell
                   [ Diagnostic
                       Error
                       ( printf
                           "Position assertion failed. Asserted 0x%x, calculated 0x%x"
                           declaredPos
-                          cursor
+                          expectedPos
                       )
                       (unCommented a)
                   ]
               return (cursor, returned)
       )
-      (0 :: Integer, [])
+      (0, [])
       decls
 
-  return $ ObjTypeBody (reverse returned) a
+  return (ObjTypeBody bodyType (reverse returned) a, cur)
   where
+    checkTypesSubStructure
+      (ObjTypeBody bodyType decls _)
+      maybeIdent
+      annot =
+        let emitWarning s = tell [Diagnostic Warning s (unCommented annot)]
+         in case () of
+              ()
+                | [_] <- decls,
+                  (Union {}) <- bodyType ->
+                    emitWarning "Union with a single field. Should this be a struct?"
+              ()
+                | [_] <- decls,
+                  (Struct {}) <- bodyType,
+                  Nothing <- maybeIdent ->
+                    emitWarning "Anonymous sub-struct with single field is superfluous."
+              ()
+                | [] <- decls ->
+                    emitWarning
+                      ( printf
+                          "Empty sub-%s is superfluous."
+                          ( case bodyType of
+                              Union {} -> "union"
+                              Struct {} -> "struct"
+                          )
+                      )
+              _ -> return ()
     fUnzip xs = (fst <$> xs, snd <$> xs)
     pushApply :: Maybe (a, b) -> (Maybe a, Maybe b)
     pushApply (Just (a, b)) = (Just a, Just b)
diff --git a/src/Language/Fiddle/GenericTree.hs b/src/Language/Fiddle/GenericTree.hs
index 668c290..00824ed 100644
--- a/src/Language/Fiddle/GenericTree.hs
+++ b/src/Language/Fiddle/GenericTree.hs
@@ -174,6 +174,8 @@ instance (GToGenericSyntaxTree r f a) => (GToGenericSyntaxTree (M1 i c r) f a) w
 
 deriving instance (ToGenericSyntaxTree Identifier)
 
+deriving instance (ToGenericSyntaxTree BodyType)
+
 deriving instance (Context stage) => (ToGenericSyntaxTree (FiddleUnit stage))
 
 deriving instance (Context stage) => (ToGenericSyntaxTree (FiddleDecl stage))
@@ -206,6 +208,20 @@ instance (Context stage) => (ToGenericSyntaxTree (ObjTypeDecl stage)) where
   toGenericSyntaxTree t = case t of
     (AssertPosStatement expr a) ->
       SyntaxTreeObject "AssertPosStatement" [toGenericSyntaxTree expr] a t
+    (TypeSubStructure body mIdent a) ->
+      SyntaxTreeObject
+        "TypeSubStructure"
+        ( Data.Foldable.toList (toGenericSyntaxTree <$> body)
+            ++ Data.Foldable.toList (toGenericSyntaxTree <$> mIdent)
+        )
+        a
+        t
+    (ReservedDecl expr a) ->
+      SyntaxTreeObject
+        "ReservedDecl"
+        [toGenericSyntaxTree expr]
+        a
+        t
     (RegisterDecl mMod mIdent expr mBody a) ->
       SyntaxTreeObject
         "RegisterDecl"
diff --git a/src/Language/Fiddle/Parser.hs b/src/Language/Fiddle/Parser.hs
index 37ef34e..7eed0f2 100644
--- a/src/Language/Fiddle/Parser.hs
+++ b/src/Language/Fiddle/Parser.hs
@@ -7,8 +7,8 @@ module Language.Fiddle.Parser
   )
 where
 
-import Data.Kind (Type)
 import Data.Functor.Identity
+import Data.Kind (Type)
 import Data.Text (Text)
 import qualified Data.Text
 import Debug.Trace
@@ -28,6 +28,7 @@ type P = ParsecT S () Identity
 type A = Commented SourceSpan
 
 type Pa (a :: Stage -> (Type -> Type) -> Type -> Type) = P (a 'Stage1 F (Commented SourceSpan))
+
 type PaS (a :: (Type -> Type) -> Type -> Type) = P (a F (Commented SourceSpan))
 
 comment :: P Comment
@@ -68,9 +69,15 @@ fiddleDecl = do
           <*> defer body packageBody
       KWLocation -> LocationDecl <$> ident <*> (tok TokEq >> expression)
       KWBits -> BitsDecl <$> ident <*> (tok TokColon >> bitType)
-      KWObjtype ->
-        ObjTypeDecl <$> ident <*> (tok TokColon >> defer body objTypeBody)
-      KWObject ->
+      KWType ->
+        ObjTypeDecl
+          <$> ident
+          <*> ( do
+                  tok TokColon
+                  bt <- bodyType
+                  defer body (objTypeBody bt)
+              )
+      KWInstance ->
         ObjectDecl
           <$> ident
           <*> (tok KWAt *> expression)
@@ -114,15 +121,18 @@ objType = do
     baseObj :: P (A -> ObjType Stage1 F A)
     baseObj =
       (ReferencedObjType <$> ident)
-        <|> (AnonymousObjType <$> defer body objTypeBody)
+        <|> ( do
+                t <- bodyType
+                AnonymousObjType <$> defer body (objTypeBody t)
+            )
 
 exprInParen :: Pa Expression
 exprInParen = tok TokLParen *> expression <* tok TokRParen
 
-objTypeBody :: Pa ObjTypeBody
-objTypeBody =
+objTypeBody :: BodyType F (Commented SourceSpan) -> Pa ObjTypeBody
+objTypeBody bt =
   withMeta $
-    ObjTypeBody <$> many (objTypeDecl <* tok TokSemi)
+    ObjTypeBody bt <$> many (objTypeDecl <* tok TokSemi)
 
 objTypeDecl :: Pa ObjTypeDecl
 objTypeDecl =
@@ -132,6 +142,14 @@ objTypeDecl =
         AssertPosStatement <$> exprInParen
     )
       <|> ( do
+              tok KWReserved
+              ReservedDecl <$> exprInParen
+          )
+      <|> ( do
+              bt <- bodyType
+              TypeSubStructure <$> defer body (objTypeBody bt) <*> optionMaybe ident
+          )
+      <|> ( do
               mod <- optionMaybe modifier
               tok KWReg
               RegisterDecl mod
@@ -150,8 +168,19 @@ modifier =
           tok KWWo >> return Wo
         ]
 
+bitBodyType :: PaS BodyType
+bitBodyType =
+  withMeta $
+    (tok KWStruct >> return Struct)
+      <|> (tok KWUnion >> return Union)
+
+bodyType :: PaS BodyType
+bodyType =
+  withMeta $
+    (tok KWStruct >> return Struct) <|> (tok KWUnion >> return Union)
+
 registerBody :: Pa RegisterBody
-registerBody = withMeta $ RegisterBody <$> defer body deferredRegisterBody
+registerBody = withMeta $ RegisterBody <$> bitBodyType <*> defer body deferredRegisterBody
 
 deferredRegisterBody :: Pa DeferredRegisterBody
 deferredRegisterBody =
@@ -164,7 +193,9 @@ registerBitsDecl =
     ( do
         tok KWReserved >> ReservedBits <$> exprInParen
     )
-      <|> ( DefinedBits <$> optionMaybe modifier
+      <|> (BitsSubStructure <$> registerBody <*> optionMaybe ident)
+      <|> ( DefinedBits
+              <$> optionMaybe modifier
               <*> ident
               <*> (tok TokColon >> registerBitsTypeRef)
           )
diff --git a/src/Language/Fiddle/Tokenizer.hs b/src/Language/Fiddle/Tokenizer.hs
index 4e06b92..08f5649 100644
--- a/src/Language/Fiddle/Tokenizer.hs
+++ b/src/Language/Fiddle/Tokenizer.hs
@@ -12,29 +12,31 @@ import qualified Text.Parsec
 
 data T
   = KWAssertPos
-  | TokIdent !Text
   | KWAt
   | KWBits
   | KWEnum
-  | TokComment !Text
-  | TokDocComment !Text
+  | KWInstance
   | KWLocation
-  | KWObject
-  | KWObjtype
   | KWOption
   | KWPackage
   | KWReg
   | KWReserved
   | KWRo
-  | KWWo
   | KWRw
-  | TokLitNum !Text
+  | KWStruct
+  | KWType
+  | KWUnion
+  | KWWo
   | TokColon
   | TokComma
+  | TokComment !Text
+  | TokDocComment !Text
   | TokEq
+  | TokIdent !Text
   | TokLBrace
   | TokLBracket
   | TokLParen
+  | TokLitNum !Text
   | TokRBrace
   | TokRBracket
   | TokRParen
@@ -60,8 +62,8 @@ parseToken = spaces *> tok parseToken' <* spaces
         "bits" -> KWBits
         "enum" -> KWEnum
         "location" -> KWLocation
-        "object" -> KWObject
-        "objtype" -> KWObjtype
+        "instance" -> KWInstance
+        "type" -> KWType
         "option" -> KWOption
         "package" -> KWPackage
         "reg" -> KWReg
@@ -69,6 +71,8 @@ parseToken = spaces *> tok parseToken' <* spaces
         "wo" -> KWWo
         "rw" -> KWRw
         "reserved" -> KWReserved
+        "union" -> KWUnion
+        "struct" -> KWStruct
         "assert_pos" -> KWAssertPos
         (Data.Text.head -> h) | isDigit h -> TokLitNum str
         ident -> TokIdent ident
diff --git a/vim/syntax/fiddle.vim b/vim/syntax/fiddle.vim
index 22341a5..7d36e93 100644
--- a/vim/syntax/fiddle.vim
+++ b/vim/syntax/fiddle.vim
@@ -1,9 +1,10 @@
 syn keyword FiddlePackage option package nextgroup=FiddleIdent skipwhite
-syn keyword FiddleDecl reg object at location reserved nextgroup=FiddleIdent skipwhite
-syn keyword FiddleTypeDecl objtype regtype bits nextgroup=FiddleIdent skipwhite
+syn keyword FiddleDecl reg instance at location reserved nextgroup=FiddleIdent skipwhite
+syn keyword FiddleTypeDecl type regtype bits nextgroup=FiddleIdent skipwhite
 syn keyword FiddleEnum enum
 syn keyword FiddleBuiltin assert_pos
 syn keyword FiddleModifier wo ro rw
+syn keyword FiddleStorageClass struct union bitstruct bitunion
 
 syn match FiddleColon +:+ skipwhite nextgroup=FiddleContainedType
 syn match FiddleContainedType +[a-zA-Z0-9_]\++ contained
@@ -13,12 +14,13 @@ syn match FiddleIdent +[A-Za-z0-9_]\++ contained
 syn match FiddleComment +\/\/.*$+
 syn region FiddleDocComment start=+/\*\*+ end=+*/+
 
-syn match FiddleNumber +[0-9_]\+\([xb]\)\@!\|0x[0-9A-Fa-f][0-9A-Fa-f_]*\|0b[01]\++
+syn match FiddleNumber +\<[0-9_]\+\([xb]\)\@!\|0x[0-9A-Fa-f][0-9A-Fa-f_]*\|0b[01]\+\>+
 
 hi! link FiddleContainedType Type
 hi! link FiddleModifier StorageClass
 hi! link FiddleBuiltin Function
 hi! link FiddleEnum StorageClass
+hi! link FiddleStorageClass FiddleEnum
 hi! link FiddleDecl Type
 hi! link FiddleNumber Number
 hi! link FiddleDocComment Comment