From 12be569742d3a48bf8e3f325981121f90f3aedd6 Mon Sep 17 00:00:00 2001
From: Zachary Snow <zach@zachjs.com>
Date: Sun, 14 Jun 2020 15:56:09 -0400
Subject: [PATCH] reduce usage of maybe

---
 src/Convert/BlockDecl.hs                      |  8 +-
 src/Convert/EmptyArgs.hs                      |  4 +-
 src/Convert/Enum.hs                           |  9 +-
 src/Convert/ForDecl.hs                        | 14 +--
 src/Convert/Foreach.hs                        |  2 +-
 src/Convert/FuncRoutine.hs                    |  2 +-
 src/Convert/Interface.hs                      | 40 ++++-----
 src/Convert/Jump.hs                           |  4 +-
 src/Convert/KWArgs.hs                         |  9 +-
 src/Convert/Logic.hs                          | 19 ++--
 src/Convert/MultiplePacked.hs                 |  4 +-
 src/Convert/NestPI.hs                         | 32 +++----
 src/Convert/Package.hs                        | 32 +++----
 src/Convert/ParamType.hs                      | 10 +--
 src/Convert/SignCast.hs                       |  4 +-
 src/Convert/Simplify.hs                       |  4 +-
 src/Convert/SizeCast.hs                       |  4 +-
 src/Convert/StarPort.hs                       |  6 +-
 src/Convert/Stream.hs                         |  6 +-
 src/Convert/Struct.hs                         | 19 ++--
 src/Convert/Traverse.hs                       | 68 ++++++--------
 src/Convert/TypeOf.hs                         |  6 +-
 src/Convert/UnpackedArray.hs                  | 12 +--
 src/Language/SystemVerilog/AST/Attr.hs        |  4 +-
 src/Language/SystemVerilog/AST/Decl.hs        |  7 +-
 src/Language/SystemVerilog/AST/Expr.hs        | 15 ++--
 src/Language/SystemVerilog/AST/ModuleItem.hs  | 25 +++---
 src/Language/SystemVerilog/AST/Stmt.hs        | 12 +--
 src/Language/SystemVerilog/AST/Type.hs        |  4 +-
 src/Language/SystemVerilog/Parser/Parse.y     | 88 ++++++++++---------
 .../SystemVerilog/Parser/ParseDecl.hs         | 37 ++++----
 31 files changed, 250 insertions(+), 260 deletions(-)

diff --git a/src/Convert/BlockDecl.hs b/src/Convert/BlockDecl.hs
index fe6bf19..5584870 100644
--- a/src/Convert/BlockDecl.hs
+++ b/src/Convert/BlockDecl.hs
@@ -42,9 +42,11 @@ convertStmt (Block Seq name decls stmts) =
 convertStmt other = other
 
 splitDecl :: Decl -> (Decl, Maybe (LHS, Expr))
-splitDecl (Variable d t ident a (Just e)) =
-    (Variable d t ident a Nothing, Just (LHSIdent ident, e))
-splitDecl other = (other, Nothing)
+splitDecl (decl @ (Variable _ _ _ _ Nil)) =
+    (decl, Nothing)
+splitDecl (Variable d t ident a e) =
+    (Variable d t ident a Nil, Just (LHSIdent ident, e))
+splitDecl decl = (decl, Nothing)
 
 asgnStmt :: (LHS, Expr) -> Stmt
 asgnStmt = uncurry $ Asgn AsgnOpEq Nothing
diff --git a/src/Convert/EmptyArgs.hs b/src/Convert/EmptyArgs.hs
index 662b609..fc18b71 100644
--- a/src/Convert/EmptyArgs.hs
+++ b/src/Convert/EmptyArgs.hs
@@ -31,7 +31,7 @@ convertDescription other = other
 
 traverseFunctionsM :: ModuleItem -> Writer Idents ModuleItem
 traverseFunctionsM (MIPackageItem (Function ml t f decls stmts)) = do
-    let dummyDecl = Variable Input (Implicit Unspecified []) "_sv2v_unused" [] Nothing
+    let dummyDecl = Variable Input (Implicit Unspecified []) "_sv2v_unused" [] Nil
     decls' <- do
         if any isInput decls
             then return decls
@@ -49,6 +49,6 @@ convertExpr :: Idents -> Expr -> Expr
 convertExpr functions (Call (Ident func) (Args [] [])) =
     Call (Ident func) (Args args [])
     where args = if Set.member func functions
-            then [Just $ Number "0"]
+            then [Number "0"]
             else []
 convertExpr _ other = other
diff --git a/src/Convert/Enum.hs b/src/Convert/Enum.hs
index 79080f6..a6336ec 100644
--- a/src/Convert/Enum.hs
+++ b/src/Convert/Enum.hs
@@ -26,7 +26,7 @@ import qualified Data.Set as Set
 import Convert.Traverse
 import Language.SystemVerilog.AST
 
-type EnumInfo = (Type, [(Identifier, Maybe Expr)])
+type EnumInfo = (Type, [(Identifier, Expr)])
 type Enums = Set.Set EnumInfo
 
 convert :: [AST] -> [AST]
@@ -84,10 +84,9 @@ makeEnumItems (itemType, l) =
         keys = map fst l
         vals = tail $ scanl step (Number "-1") (map snd l)
         noDuplicates = all (null . tail . flip elemIndices vals) vals
-        step :: Expr -> Maybe Expr -> Expr
-        step _ (Just expr) = expr
-        step expr Nothing =
-            simplify $ BinOp Add expr (Number "1")
+        step :: Expr -> Expr -> Expr
+        step expr Nil = simplify $ BinOp Add expr (Number "1")
+        step _ expr = expr
         toPackageItem :: Identifier -> Expr -> PackageItem
         toPackageItem x v =
             Decl $ Param Localparam itemType x v'
diff --git a/src/Convert/ForDecl.hs b/src/Convert/ForDecl.hs
index 05e921d..8eb9d93 100644
--- a/src/Convert/ForDecl.hs
+++ b/src/Convert/ForDecl.hs
@@ -23,7 +23,7 @@ convertStmt (For (Left []) cc asgns stmt) =
     convertStmt $ For (Right []) cc asgns stmt
 convertStmt (For (Right []) cc asgns stmt) =
     convertStmt $ For inits cc asgns stmt
-    where inits = Left [dummyDecl (Just $ Number "0")]
+    where inits = Left [dummyDecl $ Number "0"]
 convertStmt (orig @ (For (Right [_]) _ _ _)) = orig
 
 convertStmt (For (Left inits) cc asgns stmt) =
@@ -47,13 +47,15 @@ convertStmt (For (Right origPairs) cc asgns stmt) =
 convertStmt other = other
 
 splitDecl :: Decl -> (Decl, (LHS, Expr))
-splitDecl (Variable d t ident a (Just e)) =
-    (Variable d t ident a Nothing, (LHSIdent ident, e))
-splitDecl other =
-    error $ "invalid for loop decl: " ++ show other
+splitDecl (decl @ (Variable _ _ _ _ Nil)) =
+    error $ "invalid for loop decl: " ++ show decl
+splitDecl (Variable d t ident a e) =
+    (Variable d t ident a Nil, (LHSIdent ident, e))
+splitDecl decl =
+    error $ "invalid for loop decl: " ++ show decl
 
 asgnStmt :: (LHS, Expr) -> Stmt
 asgnStmt = uncurry $ Asgn AsgnOpEq Nothing
 
-dummyDecl :: Maybe Expr -> Decl
+dummyDecl :: Expr -> Decl
 dummyDecl = Variable Local (IntegerAtom TInteger Unspecified) "_sv2v_dummy" []
diff --git a/src/Convert/Foreach.hs b/src/Convert/Foreach.hs
index 458ef99..c261b3c 100644
--- a/src/Convert/Foreach.hs
+++ b/src/Convert/Foreach.hs
@@ -29,7 +29,7 @@ convertStmt (Foreach x idxs stmt) =
             where
                 queryFn f = DimFn f (Right $ Ident x) (Number $ show d)
                 idxDecl = Variable Local (IntegerAtom TInteger Unspecified) i []
-                    $ Just $ queryFn FnLeft
+                    (queryFn FnLeft)
                 cmp =
                     Mux (BinOp Eq (queryFn FnIncrement) (Number "1"))
                         (BinOp Ge (Ident i) (queryFn FnRight))
diff --git a/src/Convert/FuncRoutine.hs b/src/Convert/FuncRoutine.hs
index 0c92e5d..1a3357b 100644
--- a/src/Convert/FuncRoutine.hs
+++ b/src/Convert/FuncRoutine.hs
@@ -41,5 +41,5 @@ convertStmt functions (Subroutine (Ident func) args) =
     where
         t = TypeOf e
         e = Call (Ident func) args
-        decl = Variable Local t "sv2v_void" [] (Just e)
+        decl = Variable Local t "sv2v_void" [] e
 convertStmt _ other = other
diff --git a/src/Convert/Interface.hs b/src/Convert/Interface.hs
index 1b44573..72c9dae 100644
--- a/src/Convert/Interface.hs
+++ b/src/Convert/Interface.hs
@@ -103,8 +103,8 @@ convertDescription interfaces modules (Part attrs extern Module lifetime name po
                         Just res -> snd res
                         Nothing -> error $ "could not find interface " ++ show interfaceName
                 mapper (dir, port, expr) =
-                    Variable dir mpt (ident ++ "_" ++ port) mprs Nothing
-                    where (mpt, mprs) = lookupType interfaceItems (fromJust expr)
+                    Variable dir mpt (ident ++ "_" ++ port) mprs Nil
+                    where (mpt, mprs) = lookupType interfaceItems expr
         mapInterface (Instance part params ident Nothing instancePorts) =
             -- expand modport port bindings
             case Map.lookup part interfaces of
@@ -125,15 +125,15 @@ convertDescription interfaces modules (Part attrs extern Module lifetime name po
             traverseExprs (traverseNestedExprs $ convertExpr its mps) .
             traverseLHSs  (traverseNestedLHSs  $ convertLHS  its mps)
             where
-                locals = Set.fromList $ mapMaybe declVarIdent decls
+                locals = Set.fromList $ map declVarIdent decls
                 its = Map.withoutKeys instances locals
                 mps = Map.withoutKeys modports  locals
-                declVarIdent :: Decl -> Maybe Identifier
-                declVarIdent (Variable _ _ x _ _) = Just x
-                declVarIdent _ = Nothing
+                declVarIdent :: Decl -> Identifier
+                declVarIdent (Variable _ _ x _ _) = x
+                declVarIdent _ = ""
 
         expandPortBinding :: Identifier -> PortBinding -> Int -> [PortBinding]
-        expandPortBinding _ (origBinding @ (portName, Just (Dot (Ident instanceName) modportName))) _ =
+        expandPortBinding _ (origBinding @ (portName, Dot (Ident instanceName) modportName)) _ =
             -- expand instance modport bound to a modport
             if Map.member instanceName instances && modportDecls /= Nothing
                 then expandPortBinding' portName instanceName $ fromJust modportDecls
@@ -141,7 +141,7 @@ convertDescription interfaces modules (Part attrs extern Module lifetime name po
             where
                 interfaceName = instances Map.! instanceName
                 modportDecls = lookupModport interfaceName modportName
-        expandPortBinding moduleName (origBinding @ (portName, Just (Ident ident))) idx =
+        expandPortBinding moduleName (origBinding @ (portName, Ident ident)) idx =
             case (instances Map.!? ident, modports Map.!? ident) of
                 (Nothing, Nothing) -> [origBinding]
                 (Just interfaceName, _) ->
@@ -176,17 +176,17 @@ convertDescription interfaces modules (Part attrs extern Module lifetime name po
                 (_, Just modportDecls) ->
                     -- modport directly bound to a modport
                     expandPortBinding' portName ident $ map redirect modportDecls
-                    where redirect (d, x, _) = (d, x, Just $ Ident x)
+                    where redirect (d, x, _) = (d, x, Ident x)
         expandPortBinding _ other _ = [other]
 
         expandPortBinding' :: Identifier -> Identifier -> [ModportDecl] -> [PortBinding]
         expandPortBinding' portName instanceName modportDecls =
             map mapper modportDecls
             where
-                mapper (_, x, me) = (x', me')
+                mapper (_, x, e) = (x', e')
                     where
                         x' = if null portName then "" else portName ++ '_' : x
-                        me' = fmap (traverseNestedExprs prefixExpr) me
+                        e' = traverseNestedExprs prefixExpr e
                 prefixExpr :: Expr -> Expr
                 prefixExpr (Ident x) = Ident (instanceName ++ '_' : x)
                 prefixExpr other = other
@@ -217,7 +217,7 @@ convertDescription interfaces modules (Part attrs extern Module lifetime name po
                     interfaceItems
                 collectModportDecls :: ModuleItem -> Writer [ModportDecl] ()
                 collectModportDecls (MIPackageItem (Decl (Variable d _ x _ _))) =
-                    tell [(d', x, Just $ Ident x)]
+                    tell [(d', x, Ident x)]
                     where d' = if d == Local then Inout else d
                 collectModportDecls _ = return ()
 
@@ -251,10 +251,10 @@ prefixModuleItems prefix =
     traverseLHSs  (traverseNestedLHSs  prefixLHS )
     where
         prefixDecl :: Decl -> Decl
-        prefixDecl (Variable d t x a me) = Variable d t (prefix x) a me
-        prefixDecl (Param    s t x    e) = Param    s t (prefix x)    e
-        prefixDecl (ParamType  s x   mt) = ParamType  s (prefix x)   mt
-        prefixDecl (CommentDecl       c) = CommentDecl                c
+        prefixDecl (Variable d t x a e) = Variable d t (prefix x) a e
+        prefixDecl (Param    s t x   e) = Param    s t (prefix x)   e
+        prefixDecl (ParamType  s x  mt) = ParamType  s (prefix x)  mt
+        prefixDecl (CommentDecl      c) = CommentDecl               c
         prefixExpr :: Expr -> Expr
         prefixExpr (Ident x) = Ident (prefix x)
         prefixExpr other = other
@@ -343,8 +343,8 @@ inlineInterface (ports, items) (instanceName, instanceParams, instancePorts) =
             zip instancePortNames instancePortExprs
 
         removeDeclDir :: ModuleItem -> ModuleItem
-        removeDeclDir (MIPackageItem (Decl (Variable _ t x a me))) =
-            MIPackageItem $ Decl $ Variable Local t x a me
+        removeDeclDir (MIPackageItem (Decl (Variable _ t x a e))) =
+            MIPackageItem $ Decl $ Variable Local t x a e
         removeDeclDir other = other
         removeModport :: ModuleItem -> ModuleItem
         removeModport (Modport x _) =
@@ -370,11 +370,11 @@ inlineInterface (ports, items) (instanceName, instanceParams, instancePorts) =
         overrideParam other = other
 
         portBindingItem :: PortBinding -> Maybe ModuleItem
-        portBindingItem (ident, Just expr) =
+        portBindingItem (_, Nil) = Nothing
+        portBindingItem (ident, expr) =
             Just $ if declDirs Map.! ident == Input
                 then Assign AssignOptionNone (LHSIdent ident) expr
                 else Assign AssignOptionNone (toLHS expr) (Ident ident)
-        portBindingItem (_, Nothing) = Nothing
 
         declDirs = execWriter $
             mapM (collectDeclsM collectDeclDir) itemsPrefixed
diff --git a/src/Convert/Jump.hs b/src/Convert/Jump.hs
index 5eb99ad..d76ebfa 100644
--- a/src/Convert/Jump.hs
+++ b/src/Convert/Jump.hs
@@ -77,7 +77,7 @@ addJumpStateDeclTF :: [Decl] -> [Stmt] -> ([Decl], [Stmt])
 addJumpStateDeclTF decls stmts =
     if uses && not declares then
         ( decls ++
-            [Variable Local jumpStateType jumpState [] (Just jsNone)]
+            [Variable Local jumpStateType jumpState [] jsNone]
         , stmts )
     else if uses then
         (decls, stmts)
@@ -256,7 +256,7 @@ convertLoop loop comp stmt = do
             ]
     let jsStackIdent = jumpState ++ "_" ++ show origLoopDepth
     let jsStackDecl = Variable Local jumpStateType jsStackIdent []
-                        (Just $ Ident jumpState)
+                        (Ident jumpState)
     let jsStackRestore = If NoCheck
                 (BinOp Ne (Ident jumpState) jsReturn)
                 (asgn jumpState (Ident jsStackIdent))
diff --git a/src/Convert/KWArgs.hs b/src/Convert/KWArgs.hs
index 8e62ae6..549f41f 100644
--- a/src/Convert/KWArgs.hs
+++ b/src/Convert/KWArgs.hs
@@ -10,7 +10,6 @@
 module Convert.KWArgs (convert) where
 
 import Data.List (elemIndex, sortOn)
-import Data.Maybe (mapMaybe)
 import Control.Monad.Writer
 import qualified Data.Map.Strict as Map
 
@@ -39,11 +38,11 @@ collectTF _ = return ()
 
 collectTFDecls :: Identifier -> [Decl] -> Writer TFs ()
 collectTFDecls name decls =
-    tell $ Map.singleton name $ mapMaybe getInput decls
+    tell $ Map.singleton name $ filter (not . null) $ map getInput decls
     where
-        getInput :: Decl -> Maybe Identifier
-        getInput (Variable Input _ ident _ _) = Just ident
-        getInput _ = Nothing
+        getInput :: Decl -> Identifier
+        getInput (Variable Input _ ident _ _) = ident
+        getInput _ = ""
 
 convertExpr :: TFs -> Expr -> Expr
 convertExpr tfs (Call expr args) =
diff --git a/src/Convert/Logic.hs b/src/Convert/Logic.hs
index 85415dd..5d9e0c4 100644
--- a/src/Convert/Logic.hs
+++ b/src/Convert/Logic.hs
@@ -102,10 +102,10 @@ convertDescription ports orig =
                     unzip $ map (uncurry fixBinding) $ zip bindings [0..]
                 newItems = concat newItemsList
                 fixBinding :: PortBinding -> Int -> (PortBinding, [ModuleItem])
-                fixBinding (portName, Just expr) portIdx =
+                fixBinding (portName, expr) portIdx =
                     if portDir /= Just Output || Set.disjoint usedIdents origIdents
-                        then ((portName, Just expr), [])
-                        else ((portName, Just tmpExpr), items)
+                        then ((portName, expr), [])
+                        else ((portName, tmpExpr), items)
                     where
                         portDir = lookupPortDir portName portIdx
                         usedIdents = execWriter $
@@ -115,7 +115,7 @@ convertDescription ports orig =
                         t = Net (NetType TWire) Unspecified
                                 [(DimsFn FnBits $ Right expr, Number "1")]
                         items =
-                            [ MIPackageItem $ Decl $ Variable Local t tmp [] Nothing
+                            [ MIPackageItem $ Decl $ Variable Local t tmp [] Nil
                             , AlwaysC AlwaysComb $ Asgn AsgnOpEq Nothing lhs tmpExpr]
                         lhs = case exprToLHS expr of
                             Just l -> l
@@ -123,7 +123,6 @@ convertDescription ports orig =
                                 error $ "bad non-lhs, non-net expr "
                                     ++ show expr ++ " connected to output port "
                                     ++ portName ++ " of " ++ instanceName
-                fixBinding other _ = (other, [])
                 lookupPortDir :: Identifier -> Int -> Maybe Direction
                 lookupPortDir "" portIdx =
                     case Map.lookup moduleName ports of
@@ -138,8 +137,8 @@ convertDescription ports orig =
         fixModuleItem other = other
 
         -- rewrite variable declarations to have the correct type
-        convertModuleItem (MIPackageItem (Decl (Variable dir (IntegerVector _ sg mr) ident a me))) =
-            MIPackageItem $ Decl $ Variable dir' (t mr) ident a me
+        convertModuleItem (MIPackageItem (Decl (Variable dir (IntegerVector _ sg mr) ident a e))) =
+            MIPackageItem $ Decl $ Variable dir' (t mr) ident a e
             where
                 t = if Set.member ident fixedIdents
                     then IntegerVector TReg sg
@@ -153,8 +152,8 @@ convertDescription ports orig =
         convertDecl :: Decl -> Decl
         convertDecl (Param s (IntegerVector _ sg rs) x e) =
             Param s (Implicit sg rs) x e
-        convertDecl (Variable d (IntegerVector TLogic sg rs) x a me) =
-            Variable d (IntegerVector TReg sg rs) x a me
+        convertDecl (Variable d (IntegerVector TLogic sg rs) x a e) =
+            Variable d (IntegerVector TReg sg rs) x a e
         convertDecl other = other
 
 regIdents :: ModuleItem -> Writer Idents ()
@@ -180,7 +179,7 @@ traverseStmtM :: Stmt -> StateT Idents (Writer Idents) Stmt
 traverseStmtM (Timing _ stmt) = traverseStmtM stmt
 traverseStmtM (Subroutine (Ident f) args) = do
     case args of
-        Args [_, Just (Ident x), _] [] ->
+        Args [_, Ident x, _] [] ->
             -- assuming that no one will readmem into a local variable
             if f == "$readmemh" || f == "$readmemb"
                 then lift $ tell $ Set.singleton x
diff --git a/src/Convert/MultiplePacked.hs b/src/Convert/MultiplePacked.hs
index 6454695..9ac846d 100644
--- a/src/Convert/MultiplePacked.hs
+++ b/src/Convert/MultiplePacked.hs
@@ -47,9 +47,9 @@ convertDescription other = other
 
 -- collects and converts declarations with multiple packed dimensions
 traverseDeclM :: Decl -> State Info Decl
-traverseDeclM (Variable dir t ident a me) = do
+traverseDeclM (Variable dir t ident a e) = do
     t' <- traverseTypeM t a ident
-    return $ Variable dir t' ident a me
+    return $ Variable dir t' ident a e
 traverseDeclM (Param s t ident e) = do
     t' <- traverseTypeM t [] ident
     return $ Param s t' ident e
diff --git a/src/Convert/NestPI.hs b/src/Convert/NestPI.hs
index 1bf984d..8cb076c 100644
--- a/src/Convert/NestPI.hs
+++ b/src/Convert/NestPI.hs
@@ -26,15 +26,15 @@ convert =
             (traverseDescriptions . convertDescription)
         isPI :: Description -> Bool
         isPI (PackageItem Import{}) = False
-        isPI (PackageItem item) = piName item /= Nothing
+        isPI (PackageItem item) = piName item /= ""
         isPI _ = False
 
 -- collects packages items missing
 collectDescriptionM :: Description -> Writer PIs ()
 collectDescriptionM (PackageItem item) = do
     case piName item of
-        Nothing -> return ()
-        Just ident -> tell $ Map.singleton ident item
+        "" -> return ()
+        ident -> tell $ Map.singleton ident item
 collectDescriptionM _ = return ()
 
 -- nests packages items missing from modules
@@ -77,8 +77,8 @@ addItems _ _ [] = []
 collectPIsM :: ModuleItem -> Writer Idents ()
 collectPIsM (MIPackageItem item) =
     case piName item of
-        Nothing -> return ()
-        Just ident -> tell $ Set.singleton ident
+        "" -> return ()
+        ident -> tell $ Set.singleton ident
 collectPIsM _ = return ()
 
 -- writes down the names of subroutine invocations
@@ -98,14 +98,14 @@ collectTypenamesM (Alias _ x _) = tell $ Set.singleton x
 collectTypenamesM _ = return ()
 
 -- returns the "name" of a package item, if it has one
-piName :: PackageItem -> Maybe Identifier
-piName (Function _ _ ident _ _) = Just ident
-piName (Task     _   ident _ _) = Just ident
-piName (Typedef    _ ident    ) = Just ident
-piName (Decl (Variable _ _ ident _ _)) = Just ident
-piName (Decl (Param    _ _ ident   _)) = Just ident
-piName (Decl (ParamType  _ ident   _)) = Just ident
-piName (Decl (CommentDecl          _)) = Nothing
-piName (Import x y) = Just $ show $ Import x y
-piName (Export    _) = Nothing
-piName (Directive _) = Nothing
+piName :: PackageItem -> Identifier
+piName (Function _ _ ident _ _) = ident
+piName (Task     _   ident _ _) = ident
+piName (Typedef    _ ident    ) = ident
+piName (Decl (Variable _ _ ident _ _)) = ident
+piName (Decl (Param    _ _ ident   _)) = ident
+piName (Decl (ParamType  _ ident   _)) = ident
+piName (Decl (CommentDecl          _)) = ""
+piName (Import x y) = show $ Import x y
+piName (Export    _) = ""
+piName (Directive _) = ""
diff --git a/src/Convert/Package.hs b/src/Convert/Package.hs
index 73b3df6..00903a3 100644
--- a/src/Convert/Package.hs
+++ b/src/Convert/Package.hs
@@ -98,7 +98,7 @@ prefixPackageItem packageName idents item =
         convertType (Enum t items rs) = Enum t items' rs
             where
                 items' = map prefixItem items
-                prefixItem (x, me) = (prefix x, me)
+                prefixItem (x, e) = (prefix x, e)
         convertType other = other
         convertExpr (Ident x) = Ident $ prefix x
         convertExpr other = other
@@ -120,8 +120,8 @@ collectDescriptionM (Package _ name items) =
         toPackageItems :: PackageItem -> PackageItems
         toPackageItems item =
             case piName item of
-                Nothing -> []
-                Just x -> [(x, item)]
+                "" -> []
+                x -> [(x, item)]
         isImport :: PackageItem -> Bool
         isImport (Import _ _) = True
         isImport _ = False
@@ -146,8 +146,8 @@ traverseDescription packages description =
         writePIName :: ModuleItem -> Writer Idents ()
         writePIName (MIPackageItem item) =
             case piName item of
-                Nothing -> return ()
-                Just x -> tell $ Set.singleton x
+                "" -> return ()
+                x -> tell $ Set.singleton x
         writePIName _ = return ()
 
 traverseModuleItem :: Idents -> Packages -> ModuleItem -> ModuleItem
@@ -177,14 +177,14 @@ traverseModuleItem _ _ item =
         traverseType other = other
 
 -- returns the "name" of a package item, if it has one
-piName :: PackageItem -> Maybe Identifier
-piName (Function _ _ ident _ _) = Just ident
-piName (Task     _   ident _ _) = Just ident
-piName (Typedef    _ ident    ) = Just ident
-piName (Decl (Variable _ _ ident _ _)) = Just ident
-piName (Decl (Param    _ _ ident   _)) = Just ident
-piName (Decl (ParamType  _ ident   _)) = Just ident
-piName (Decl (CommentDecl          _)) = Nothing
-piName (Import  _ _) = Nothing
-piName (Export    _) = Nothing
-piName (Directive _) = Nothing
+piName :: PackageItem -> Identifier
+piName (Function _ _ ident _ _) = ident
+piName (Task     _   ident _ _) = ident
+piName (Typedef    _ ident    ) = ident
+piName (Decl (Variable _ _ ident _ _)) = ident
+piName (Decl (Param    _ _ ident   _)) = ident
+piName (Decl (ParamType  _ ident   _)) = ident
+piName (Decl (CommentDecl          _)) = ""
+piName (Import  _ _) = ""
+piName (Export    _) = ""
+piName (Directive _) = ""
diff --git a/src/Convert/ParamType.hs b/src/Convert/ParamType.hs
index c2fa02a..aff0c17 100644
--- a/src/Convert/ParamType.hs
+++ b/src/Convert/ParamType.hs
@@ -99,11 +99,11 @@ convert files =
             where
                 maybeTypeMap = snd $ info Map.! name
                 typeMap = defaultInstance maybeTypeMap
-                existingNames = map maybeModuleName existing
-                alreadyExists = (flip elem existingNames) . maybeModuleName
-                maybeModuleName :: Description -> Maybe Identifier
-                maybeModuleName (Part _ _ _ _ x _ _) = Just x
-                maybeModuleName _ = Nothing
+                existingNames = map moduleName existing
+                alreadyExists = (flip elem existingNames) . moduleName
+                moduleName :: Description -> Identifier
+                moduleName (Part _ _ _ _ x _ _) = x
+                moduleName _ = ""
         replaceDefault _ other = [other]
 
         removeDefaultTypeParams :: Description -> Description
diff --git a/src/Convert/SignCast.hs b/src/Convert/SignCast.hs
index f3fa3eb..e879d82 100644
--- a/src/Convert/SignCast.hs
+++ b/src/Convert/SignCast.hs
@@ -23,7 +23,7 @@ convert =
 
 convertExpr :: Expr -> Expr
 convertExpr (Cast (Left (Implicit Signed [])) e) =
-    Call (Ident "$signed") (Args [Just e] [])
+    Call (Ident "$signed") (Args [e] [])
 convertExpr (Cast (Left (Implicit Unsigned [])) e) =
-    Call (Ident "$unsigned") (Args [Just e] [])
+    Call (Ident "$unsigned") (Args [e] [])
 convertExpr other = other
diff --git a/src/Convert/Simplify.hs b/src/Convert/Simplify.hs
index d99bc75..25d7ba0 100644
--- a/src/Convert/Simplify.hs
+++ b/src/Convert/Simplify.hs
@@ -70,13 +70,13 @@ convertExpr info (DimFn f v e) =
     DimFn f v e'
     where
         e' = simplify $ substitute info e
-convertExpr info (Call (Ident "$clog2") (Args [Just e] [])) =
+convertExpr info (Call (Ident "$clog2") (Args [e] [])) =
     if clog2' == clog2
         then clog2
         else clog2'
     where
         e' = simplify $ substitute info e
-        clog2 = Call (Ident "$clog2") (Args [Just e'] [])
+        clog2 = Call (Ident "$clog2") (Args [e'] [])
         clog2' = simplify clog2
 convertExpr info (Mux cc aa bb) =
     if before == after
diff --git a/src/Convert/SizeCast.hs b/src/Convert/SizeCast.hs
index 9f7d193..2c46b98 100644
--- a/src/Convert/SizeCast.hs
+++ b/src/Convert/SizeCast.hs
@@ -97,7 +97,7 @@ traverseExprM =
         convertCastWithSigningM s e sg = do
             lift $ tell $ Set.singleton (s, sg)
             let f = castFnName s sg
-            let args = Args [Just e] []
+            let args = Args [e] []
             return $ Call (Ident f) args
 
 castFn :: Expr -> Signing -> Description
@@ -109,7 +109,7 @@ castFn e sg =
         r = (simplify $ BinOp Sub e (Number "1"), Number "0")
         t = IntegerVector TLogic sg [r]
         fnName = castFnName e sg
-        decl = Variable Input t inp [] Nothing
+        decl = Variable Input t inp [] Nil
 
 castFnName :: Expr -> Signing -> String
 castFnName e sg =
diff --git a/src/Convert/StarPort.hs b/src/Convert/StarPort.hs
index 549311e..50dc50b 100644
--- a/src/Convert/StarPort.hs
+++ b/src/Convert/StarPort.hs
@@ -31,12 +31,12 @@ mapInstance modulePorts (Instance m p x r bindings) =
         alreadyBound :: [Identifier]
         alreadyBound = map fst bindings
         expandBinding :: PortBinding -> [PortBinding]
-        expandBinding ("*", Nothing) =
+        expandBinding ("*", Nil) =
             case Map.lookup m modulePorts of
                 Just l ->
-                    map (\port -> (port, Just $ Ident port)) $
+                    map (\port -> (port, Ident port)) $
                     filter (\s -> not $ elem s alreadyBound) $ l
                 -- if we can't find it, just skip :(
-                Nothing -> [("*", Nothing)]
+                Nothing -> [("*", Nil)]
         expandBinding other = [other]
 mapInstance _ other = other
diff --git a/src/Convert/Stream.hs b/src/Convert/Stream.hs
index 081abc8..312a31b 100644
--- a/src/Convert/Stream.hs
+++ b/src/Convert/Stream.hs
@@ -20,9 +20,9 @@ convertDescription other = other
 streamerBlock :: Expr -> Expr -> (LHS -> Expr -> Stmt) -> LHS -> Expr -> Stmt
 streamerBlock chunk size asgn output input =
     Block Seq ""
-    [ Variable Local t inp [] $ Just input
-    , Variable Local t out [] Nothing
-    , Variable Local (IntegerAtom TInteger Unspecified) idx [] Nothing
+    [ Variable Local t inp [] input
+    , Variable Local t out [] Nil
+    , Variable Local (IntegerAtom TInteger Unspecified) idx [] Nil
     ]
     [ For inits cmp incr stmt
     , If NoCheck cmp2 stmt2 Null
diff --git a/src/Convert/Struct.hs b/src/Convert/Struct.hs
index 8aa7581..a833c55 100644
--- a/src/Convert/Struct.hs
+++ b/src/Convert/Struct.hs
@@ -189,16 +189,13 @@ collectTFArgsM _ = return ()
 traverseDeclM :: Structs -> Decl -> State Types Decl
 traverseDeclM structs origDecl = do
     case origDecl of
-        Variable d t x a me -> do
+        Variable d t x a e -> do
             let (tf, rs) = typeRanges t
             if isRangeable t
                 then modify $ Map.insert x (tf $ a ++ rs)
                 else return ()
-            case me of
-                Nothing -> return origDecl
-                Just e -> do
-                    e' <- convertDeclExpr x e
-                    return $ Variable d t x a (Just e')
+            e' <- convertDeclExpr x e
+            return $ Variable d t x a e'
         Param s t x e -> do
             modify $ Map.insert x t
             e' <- convertDeclExpr x e
@@ -223,7 +220,7 @@ packerFn structTf =
     Function Automatic (structTf []) fnName decls [retStmt]
     where
         Struct _ fields [] = structTf []
-        toInput (t, x) = Variable Input t x [] Nothing
+        toInput (t, x) = Variable Input t x [] Nil
         decls = map toInput fields
         retStmt = Return $ Concat $ map (Ident . snd) fields
         fnName = packerFnName structTf
@@ -269,6 +266,7 @@ convertAsgn structs types (lhs, expr) =
 
         -- try expression conversion by looking at the *outermost* type first
         convertExpr :: Type -> Expr -> Expr
+        convertExpr _ Nil = Nil
         convertExpr t (Mux c e1 e2) =
             Mux c e1' e2'
             where
@@ -316,7 +314,7 @@ convertAsgn structs types (lhs, expr) =
             else if Map.member structTf structs then
                 Call
                     (Ident $ packerFnName structTf)
-                    (Args (map (Just . snd) items) [])
+                    (Args (map snd items) [])
             else
                 Pattern items
             where
@@ -551,9 +549,8 @@ convertCall structs types fn (Args pnArgs kwArgs) =
         args = Args
             (map snd $ map convertArg $ zip idxs pnArgs)
             (map convertArg kwArgs)
-        convertArg :: (Identifier, Maybe Expr) -> (Identifier, Maybe Expr)
-        convertArg (x, Nothing) = (x, Nothing)
-        convertArg (x, Just e ) = (x, Just e')
+        convertArg :: (Identifier, Expr) -> (Identifier, Expr)
+        convertArg (x, e) = (x, e')
             where
                 (_, e') = convertAsgn structs types
                     (LHSIdent $ f ++ ":" ++ x, e)
diff --git a/src/Convert/Traverse.hs b/src/Convert/Traverse.hs
index 3dc7b4b..e9bb5bc 100644
--- a/src/Convert/Traverse.hs
+++ b/src/Convert/Traverse.hs
@@ -300,13 +300,10 @@ traverseAssertionExprsM mapper = assertionMapper
             c' <- mapper c
             return $ Left (a, b, c')
         seqMatchItemMapper (Right (x, (Args l p))) = do
-            l' <- mapM maybeExprMapper l
-            pes <- mapM maybeExprMapper $ map snd p
+            l' <- mapM mapper l
+            pes <- mapM mapper $ map snd p
             let p' = zip (map fst p) pes
             return $ Right (x, Args l' p')
-        maybeExprMapper Nothing = return Nothing
-        maybeExprMapper (Just e) =
-            mapper e >>= return . Just
         ppMapper constructor p1 p2 = do
             p1' <- propExprMapper p1
             p2' <- propExprMapper p2
@@ -331,10 +328,10 @@ traverseAssertionExprsM mapper = assertionMapper
             spMapper PropExprFollowsNO se pe
         propExprMapper (PropExprIff p1 p2) =
             ppMapper PropExprIff p1 p2
-        propSpecMapper (PropertySpec ms me pe) = do
-            me' <- maybeExprMapper me
+        propSpecMapper (PropertySpec ms e pe) = do
+            e' <- mapper e
             pe' <- propExprMapper pe
-            return $ PropertySpec ms me' pe'
+            return $ PropertySpec ms e' pe'
         assertionExprMapper (Left e) =
             propSpecMapper e >>= return . Left
         assertionExprMapper (Right e) =
@@ -408,10 +405,7 @@ traverseNestedExprsM :: Monad m => MapperM m Expr -> MapperM m Expr
 traverseNestedExprsM mapper = exprMapper
     where
         exprMapper e = mapper e >>= em
-        (_, _, _, _, typeMapper) = exprMapperHelpers exprMapper
-        maybeExprMapper Nothing = return Nothing
-        maybeExprMapper (Just e) =
-            exprMapper e >>= return . Just
+        (_, _, _, typeMapper) = exprMapperHelpers exprMapper
         typeOrExprMapper (Left t) =
             typeMapper t >>= return . Left
         typeOrExprMapper (Right e) =
@@ -448,8 +442,8 @@ traverseNestedExprsM mapper = exprMapper
             return $ Stream o e' l'
         em (Call  e (Args l p)) = do
             e' <- exprMapper e
-            l' <- mapM maybeExprMapper l
-            pes <- mapM maybeExprMapper $ map snd p
+            l' <- mapM exprMapper l
+            pes <- mapM exprMapper $ map snd p
             let p' = zip (map fst p) pes
             return $ Call e' (Args l' p')
         em (UniOp      o e) =
@@ -493,9 +487,9 @@ traverseNestedExprsM mapper = exprMapper
         em (Nil) = return Nil
 
 exprMapperHelpers :: Monad m => MapperM m Expr ->
-    (MapperM m Range, MapperM m (Maybe Expr), MapperM m Decl, MapperM m LHS, MapperM m Type)
+    (MapperM m Range, MapperM m Decl, MapperM m LHS, MapperM m Type)
 exprMapperHelpers exprMapper =
-    (rangeMapper, maybeExprMapper, declMapper, traverseNestedLHSsM lhsMapper, typeMapper)
+    (rangeMapper, declMapper, traverseNestedLHSsM lhsMapper, typeMapper)
     where
 
     rangeMapper (a, b) = do
@@ -503,10 +497,6 @@ exprMapperHelpers exprMapper =
         b' <- exprMapper b
         return (a', b')
 
-    maybeExprMapper Nothing = return Nothing
-    maybeExprMapper (Just e) =
-        exprMapper e >>= return . Just
-
     typeMapper' (TypeOf expr) =
         exprMapper expr >>= return . TypeOf
     typeMapper' t = do
@@ -526,11 +516,11 @@ exprMapperHelpers exprMapper =
     declMapper (ParamType s x mt) = do
         mt' <- maybeTypeMapper mt
         return $ ParamType s x mt'
-    declMapper (Variable d t x a me) = do
+    declMapper (Variable d t x a e) = do
         t' <- typeMapper t
         a' <- mapM rangeMapper a
-        me' <- maybeExprMapper me
-        return $ Variable d t' x a' me'
+        e' <- exprMapper e
+        return $ Variable d t' x a' e'
     declMapper (CommentDecl c) =
         return $ CommentDecl c
 
@@ -547,13 +537,13 @@ traverseExprsM' :: Monad m => TFStrategy -> MapperM m Expr -> MapperM m ModuleIt
 traverseExprsM' strat exprMapper = moduleItemMapper
     where
 
-    (rangeMapper, maybeExprMapper, declMapper, lhsMapper, typeMapper)
+    (rangeMapper, declMapper, lhsMapper, typeMapper)
         = exprMapperHelpers exprMapper
 
     stmtMapper = traverseNestedStmtsM (traverseStmtExprsM exprMapper)
 
-    portBindingMapper (p, me) =
-        maybeExprMapper me >>= \me' -> return (p, me')
+    portBindingMapper (p, e) =
+        exprMapper e >>= \e' -> return (p, e')
 
     paramBindingMapper (p, Left t) =
         typeMapper t >>= \t' -> return (p, Left t')
@@ -616,12 +606,12 @@ traverseExprsM' strat exprMapper = moduleItemMapper
     moduleItemMapper (Modport x l) =
         mapM modportDeclMapper l >>= return . Modport x
     moduleItemMapper (NInputGate  kw d x lhs exprs) = do
-        d' <- maybeExprMapper d
+        d' <- exprMapper d
         exprs' <- mapM exprMapper exprs
         lhs' <- lhsMapper lhs
         return $ NInputGate kw d' x lhs' exprs'
     moduleItemMapper (NOutputGate kw d x lhss expr) = do
-        d' <- maybeExprMapper d
+        d' <- exprMapper d
         lhss' <- mapM lhsMapper lhss
         expr' <- exprMapper expr
         return $ NOutputGate kw d' x lhss' expr'
@@ -655,10 +645,9 @@ traverseExprsM' strat exprMapper = moduleItemMapper
         return $ GenCase e' cases'
     genItemMapper other = return other
 
-    modportDeclMapper (dir, ident, Just e) = do
+    modportDeclMapper (dir, ident, e) = do
         e' <- exprMapper e
-        return (dir, ident, Just e')
-    modportDeclMapper other = return other
+        return (dir, ident, e')
 
 traverseExprs' :: TFStrategy -> Mapper Expr -> Mapper ModuleItem
 traverseExprs' strat = unmonad $ traverseExprsM' strat
@@ -676,8 +665,7 @@ traverseStmtExprsM :: Monad m => MapperM m Expr -> MapperM m Stmt
 traverseStmtExprsM exprMapper = flatStmtMapper
     where
 
-    (_, maybeExprMapper, declMapper, lhsMapper, _)
-        = exprMapperHelpers exprMapper
+    (_, declMapper, lhsMapper, _) = exprMapperHelpers exprMapper
 
     caseMapper (exprs, stmt) = do
         exprs' <- mapM exprMapper exprs
@@ -715,8 +703,8 @@ traverseStmtExprsM exprMapper = flatStmtMapper
     flatStmtMapper (Timing event stmt) = return $ Timing event stmt
     flatStmtMapper (Subroutine e (Args l p)) = do
         e' <- exprMapper e
-        l' <- mapM maybeExprMapper l
-        pes <- mapM maybeExprMapper $ map snd p
+        l' <- mapM exprMapper l
+        pes <- mapM exprMapper $ map snd p
         let p' = zip (map fst p) pes
         return $ Subroutine e' (Args l' p')
     flatStmtMapper (Return expr) =
@@ -897,7 +885,7 @@ collectExprTypesM = collectify traverseExprTypesM
 traverseTypeExprsM :: Monad m => MapperM m Expr -> MapperM m Type
 traverseTypeExprsM mapper =
     typeMapper
-    where (_, _, _, _, typeMapper) = exprMapperHelpers mapper
+    where (_, _, _, typeMapper) = exprMapperHelpers mapper
 
 traverseTypeExprs :: Mapper Expr -> Mapper Type
 traverseTypeExprs = unmonad traverseTypeExprsM
@@ -918,8 +906,8 @@ traverseTypesM' strategy mapper item =
             fullMapper t >>= \t' -> return $ Param s t' x e
         declMapper (ParamType s x mt) =
             maybeMapper mt >>= \mt' -> return $ ParamType s x mt'
-        declMapper (Variable d t x a me) =
-            fullMapper t >>= \t' -> return $ Variable d t' x a me
+        declMapper (Variable d t x a e) =
+            fullMapper t >>= \t' -> return $ Variable d t' x a e
         declMapper (CommentDecl c) = return $ CommentDecl c
         miMapper (MIPackageItem (Typedef t x)) =
             fullMapper t >>= \t' -> return $ MIPackageItem $ Typedef t' x
@@ -1111,9 +1099,9 @@ traverseScopesM declMapper moduleItemMapper stmtMapper =
         redirectModuleItem (MIPackageItem (Function ml t x decls stmts)) = do
             prevState <- get
             t' <- do
-                res <- declMapper $ Variable Local t x [] Nothing
+                res <- declMapper $ Variable Local t x [] Nil
                 case res of
-                    Variable Local newType _ [] Nothing -> return newType
+                    Variable Local newType _ [] Nil -> return newType
                     _ -> error $ "redirected func ret traverse failed: " ++ show res
             decls' <- mapM declMapper decls
             stmts' <- mapM fullStmtMapper stmts
diff --git a/src/Convert/TypeOf.hs b/src/Convert/TypeOf.hs
index d2e4088..f3c0f21 100644
--- a/src/Convert/TypeOf.hs
+++ b/src/Convert/TypeOf.hs
@@ -46,12 +46,12 @@ traverseDeclM decl = do
     item <- traverseModuleItemM (MIPackageItem $ Decl decl)
     let MIPackageItem (Decl decl') = item
     case decl' of
-        Variable d t ident a me -> do
+        Variable d t ident a e -> do
             let t' = injectRanges t a
             modify $ Map.insert ident t'
             return $ case t' of
-                UnpackedType t'' a' -> Variable d t'' ident a' me
-                _ ->                   Variable d t'  ident [] me
+                UnpackedType t'' a' -> Variable d t'' ident a' e
+                _ ->                   Variable d t'  ident [] e
         Param    _ t ident   _ -> do
             let t' = if t == Implicit Unspecified []
                         then IntegerAtom TInteger Unspecified
diff --git a/src/Convert/UnpackedArray.hs b/src/Convert/UnpackedArray.hs
index fdffbad..dc3b83f 100644
--- a/src/Convert/UnpackedArray.hs
+++ b/src/Convert/UnpackedArray.hs
@@ -40,9 +40,9 @@ convertDescription description =
 
 -- collects and converts multi-dimensional packed-array declarations
 traverseDeclM :: Decl -> ST Decl
-traverseDeclM (orig @ (Variable dir _ x _ me)) = do
+traverseDeclM (orig @ (Variable dir _ x _ e)) = do
     modify $ Map.insert x orig
-    () <- if dir /= Local || me /= Nothing
+    () <- if dir /= Local || e /= Nil
         then lift $ tell $ Set.singleton orig
         else return ()
     return orig
@@ -50,12 +50,12 @@ traverseDeclM other = return other
 
 -- pack the given decls marked for packing
 packDecl :: DeclSet -> Decl -> Decl
-packDecl decls (orig @ (Variable d t x a me)) = do
+packDecl decls (orig @ (Variable d t x a e)) = do
     if Set.member orig decls
         then do
             let (tf, rs) = typeRanges t
             let t' = tf $ a ++ rs
-            Variable d t' x [] me
+            Variable d t' x [] e
         else orig
 packDecl _ other = other
 
@@ -73,9 +73,9 @@ traverseModuleItemM' (Instance a b c d bindings) = do
     return $ Instance a b c d bindings'
     where
         collectBinding :: PortBinding -> ST PortBinding
-        collectBinding (y, Just (Ident x)) = do
+        collectBinding (y, Ident x) = do
             flatUsageM x
-            return (y, Just (Ident x))
+            return (y, Ident x)
         collectBinding other = return other
 traverseModuleItemM' other = return other
 
diff --git a/src/Language/SystemVerilog/AST/Attr.hs b/src/Language/SystemVerilog/AST/Attr.hs
index 1fd72e0..ad79c79 100644
--- a/src/Language/SystemVerilog/AST/Attr.hs
+++ b/src/Language/SystemVerilog/AST/Attr.hs
@@ -20,10 +20,10 @@ data Attr
     = Attr [AttrSpec]
     deriving Eq
 
-type AttrSpec = (Identifier, Maybe Expr)
+type AttrSpec = (Identifier, Expr)
 
 instance Show Attr where
     show (Attr specs) = printf "(* %s *)" $ commas $ map showSpec specs
 
 showSpec :: AttrSpec -> String
-showSpec (x, me) = x ++ showAssignment me
+showSpec (x, e) = x ++ showAssignment e
diff --git a/src/Language/SystemVerilog/AST/Decl.hs b/src/Language/SystemVerilog/AST/Decl.hs
index 1bff7a0..d84db21 100644
--- a/src/Language/SystemVerilog/AST/Decl.hs
+++ b/src/Language/SystemVerilog/AST/Decl.hs
@@ -22,15 +22,16 @@ import Language.SystemVerilog.AST.Expr (Expr, Range, showRanges, showAssignment)
 data Decl
     = Param     ParamScope Type Identifier Expr
     | ParamType ParamScope Identifier (Maybe Type)
-    | Variable   Direction Type Identifier [Range] (Maybe Expr)
+    | Variable   Direction Type Identifier [Range] Expr
     | CommentDecl String
     deriving (Eq, Ord)
 
 instance Show Decl where
     showList l _ = unlines' $ map show l
     show (Param s t x e) = printf "%s %s%s = %s;" (show s) (showPad t) x (show e)
-    show (ParamType s x mt) = printf "%s type %s%s;" (show s) x (showAssignment mt)
-    show (Variable d t x a me) = printf "%s%s%s%s%s;" (showPad d) (showPad t) x (showRanges a) (showAssignment me)
+    show (ParamType s x mt) = printf "%s type %s%s;" (show s) x tStr
+        where tStr = maybe "" ((" = " ++) . show) mt
+    show (Variable d t x a e) = printf "%s%s%s%s%s;" (showPad d) (showPad t) x (showRanges a) (showAssignment e)
     show (CommentDecl c) =
         if elem '\n' c
             then "// " ++ show c
diff --git a/src/Language/SystemVerilog/AST/Expr.hs b/src/Language/SystemVerilog/AST/Expr.hs
index 0e545f9..2031f8a 100644
--- a/src/Language/SystemVerilog/AST/Expr.hs
+++ b/src/Language/SystemVerilog/AST/Expr.hs
@@ -127,15 +127,14 @@ instance Show Expr where
     showsPrec _ e = \s -> show e ++ s
 
 data Args
-    = Args [Maybe Expr] [(Identifier, Maybe Expr)]
+    = Args [Expr] [(Identifier, Expr)]
     deriving (Eq, Ord)
 
 instance Show Args where
     show (Args pnArgs kwArgs) = "(" ++ (commas strs) ++ ")"
         where
-            strs = (map showPnArg pnArgs) ++ (map showKwArg kwArgs)
-            showPnArg = maybe "" show
-            showKwArg (x, me) = printf ".%s(%s)" x (showPnArg me)
+            strs = (map show pnArgs) ++ (map showKwArg kwArgs)
+            showKwArg (x, e) = printf ".%s(%s)" x (show e)
 
 data PartSelectMode
     = NonIndexed
@@ -177,9 +176,9 @@ instance Show DimFn where
     show FnSize               = "$size"
 
 
-showAssignment :: Show a => Maybe a -> String
-showAssignment Nothing = ""
-showAssignment (Just val) = " = " ++ show val
+showAssignment :: Expr -> String
+showAssignment Nil = ""
+showAssignment val = " = " ++ show val
 
 showRanges :: [Range] -> String
 showRanges [] = ""
@@ -241,7 +240,7 @@ simplify (orig @ (Repeat (Number n) exprs)) =
 simplify (Concat [expr]) = expr
 simplify (Concat exprs) =
     Concat $ filter (/= Concat []) exprs
-simplify (orig @ (Call (Ident "$clog2") (Args [Just (Number n)] []))) =
+simplify (orig @ (Call (Ident "$clog2") (Args [Number n] []))) =
     case readNumber n of
         Nothing -> orig
         Just x -> Number $ show $ clog2 x
diff --git a/src/Language/SystemVerilog/AST/ModuleItem.hs b/src/Language/SystemVerilog/AST/ModuleItem.hs
index 1cf6496..4c2b7af 100644
--- a/src/Language/SystemVerilog/AST/ModuleItem.hs
+++ b/src/Language/SystemVerilog/AST/ModuleItem.hs
@@ -17,7 +17,6 @@ module Language.SystemVerilog.AST.ModuleItem
     ) where
 
 import Data.List (intercalate)
-import Data.Maybe (fromJust, isJust)
 import Text.Printf (printf)
 
 import Language.SystemVerilog.AST.ShowHelp
@@ -43,8 +42,8 @@ data ModuleItem
     | Initial    Stmt
     | Final      Stmt
     | MIPackageItem PackageItem
-    | NInputGate  NInputGateKW  (Maybe Expr) Identifier  LHS [Expr]
-    | NOutputGate NOutputGateKW (Maybe Expr) Identifier [LHS] Expr
+    | NInputGate  NInputGateKW  Expr Identifier  LHS [Expr]
+    | NOutputGate NOutputGateKW Expr Identifier [LHS] Expr
     | AssertionItem AssertionItem
     deriving Eq
 
@@ -77,17 +76,17 @@ showPorts :: [PortBinding] -> String
 showPorts ports = indentedParenList $ map showPort ports
 
 showPort :: PortBinding -> String
-showPort ("*", Nothing) = ".*"
+showPort ("*", Nil) = ".*"
 showPort (i, arg) =
     if i == ""
-        then show (fromJust arg)
-        else printf ".%s(%s)" i (if isJust arg then show $ fromJust arg else "")
+        then show arg
+        else printf ".%s(%s)" i (show arg)
 
-showGate :: Show k => k -> Maybe Expr -> Identifier -> [String] -> String
+showGate :: Show k => k -> Expr -> Identifier -> [String] -> String
 showGate kw d x args =
     printf "%s %s%s(%s);" (show kw) delayStr nameStr (commas args)
     where
-        delayStr = maybe "" (showPad . Delay) d
+        delayStr = if d == Nil then "" else showPad $ Delay d
         nameStr = showPad $ Ident x
 
 showParams :: [ParamBinding] -> String
@@ -100,16 +99,16 @@ showParam (i, arg) =
     where fmt = if i == "" then "%s%s" else ".%s(%s)"
 
 showModportDecl :: ModportDecl -> String
-showModportDecl (dir, ident, me) =
-    if me == Just (Ident ident)
+showModportDecl (dir, ident, e) =
+    if e == Ident ident
         then printf "%s %s" (show dir) ident
-        else printf "%s .%s(%s)" (show dir) ident (maybe "" show me)
+        else printf "%s .%s(%s)" (show dir) ident (show e)
 
-type PortBinding = (Identifier, Maybe Expr)
+type PortBinding = (Identifier, Expr)
 
 type ParamBinding = (Identifier, TypeOrExpr)
 
-type ModportDecl = (Direction, Identifier, Maybe Expr)
+type ModportDecl = (Direction, Identifier, Expr)
 
 data AlwaysKW
     = Always
diff --git a/src/Language/SystemVerilog/AST/Stmt.hs b/src/Language/SystemVerilog/AST/Stmt.hs
index 31e5c66..f84de2d 100644
--- a/src/Language/SystemVerilog/AST/Stmt.hs
+++ b/src/Language/SystemVerilog/AST/Stmt.hs
@@ -244,18 +244,18 @@ showAssertionExpr (Left e) = printf "property (%s\n)" (show e)
 showAssertionExpr (Right e) = printf "(%s)" (show e)
 
 data PropertySpec
-    = PropertySpec (Maybe Sense) (Maybe Expr) PropExpr
+    = PropertySpec (Maybe Sense) Expr PropExpr
     deriving Eq
 instance Show PropertySpec where
-    show (PropertySpec ms me pe) =
-        printf "%s%s\n\t%s" msStr meStr (show pe)
+    show (PropertySpec ms e pe) =
+        printf "%s%s\n\t%s" msStr eStr (show pe)
         where
             msStr = case ms of
                 Nothing -> ""
                 Just s -> printf "@(%s) " (show s)
-            meStr = case me of
-                Nothing -> ""
-                Just e -> printf "disable iff (%s)" (show e)
+            eStr = case e of
+                Nil -> ""
+                _ -> printf "disable iff (%s)" (show e)
 
 data ViolationCheck
     = Unique
diff --git a/src/Language/SystemVerilog/AST/Type.hs b/src/Language/SystemVerilog/AST/Type.hs
index 8dfe63b..d94a374 100644
--- a/src/Language/SystemVerilog/AST/Type.hs
+++ b/src/Language/SystemVerilog/AST/Type.hs
@@ -33,7 +33,7 @@ import Language.SystemVerilog.AST.ShowHelp
 
 type Identifier = String
 
-type Item = (Identifier, Maybe Expr)
+type Item = (Identifier, Expr)
 type Field = (Type, Identifier)
 
 data Type
@@ -63,7 +63,7 @@ instance Show Type where
     show (Enum t vals r) = printf "enum %s{%s}%s" tStr (commas $ map showVal vals) (showRanges r)
         where
             tStr = showPad t
-            showVal :: (Identifier, Maybe Expr) -> String
+            showVal :: (Identifier, Expr) -> String
             showVal (x, e) = x ++ (showAssignment e)
     show (Struct p items r) = printf "struct %s{\n%s\n}%s" (showPad p) (showFields items) (showRanges r)
     show (Union  p items r) = printf  "union %s{\n%s\n}%s" (showPad p) (showFields items) (showRanges r)
diff --git a/src/Language/SystemVerilog/Parser/Parse.y b/src/Language/SystemVerilog/Parser/Parse.y
index 3903cd9..a87111a 100644
--- a/src/Language/SystemVerilog/Parser/Parse.y
+++ b/src/Language/SystemVerilog/Parser/Parse.y
@@ -509,7 +509,7 @@ NonIntegerType :: { NonIntegerType }
   | "string"    { TString    }
   | "event"     { TEvent     }
 
-EnumItems :: { [(Identifier, Maybe Expr)] }
+EnumItems :: { [(Identifier, Expr)] }
   : VariablePortIdentifiers { $1 }
 
 StructItems :: { [(Type, Identifier)] }
@@ -589,12 +589,12 @@ ModportPortsDeclaration(delim) :: { [ModportDecl] }
   : ModportSimplePortsDeclaration(delim) { $1 }
 ModportSimplePortsDeclaration(delim) :: { [ModportDecl] }
   : Direction ModportSimplePorts delim { map (\(a, b) -> ($1, a, b)) $2 }
-ModportSimplePorts :: { [(Identifier, Maybe Expr)] }
+ModportSimplePorts :: { [(Identifier, Expr)] }
   : ModportSimplePort                        { [$1] }
   | ModportSimplePorts "," ModportSimplePort { $1 ++ [$3] }
-ModportSimplePort :: { (Identifier, Maybe Expr) }
-  : "." Identifier "(" opt(Expr) ")" { ($2, $4) }
-  | Identifier                       { ($1, Just $ Ident $1) }
+ModportSimplePort :: { (Identifier, Expr) }
+  : "." Identifier "(" ExprOrNil ")" { ($2, $4) }
+  | Identifier                       { ($1, Ident $1) }
 
 Identifier :: { Identifier }
   : simpleIdentifier  { tokenString $1 }
@@ -636,12 +636,12 @@ DeclTokenAsgn :: { DeclToken }
   : "=" opt(DelayOrEvent) Expr {% posInject \p -> DTAsgn p AsgnOpEq $2 $3 }
   | AsgnBinOp Expr             {% posInject \p -> DTAsgn p $1 Nothing $2 }
 
-VariablePortIdentifiers :: { [(Identifier, Maybe Expr)] }
+VariablePortIdentifiers :: { [(Identifier, Expr)] }
   : VariablePortIdentifier                             { [$1] }
   | VariablePortIdentifiers "," VariablePortIdentifier { $1 ++ [$3] }
-VariablePortIdentifier :: { (Identifier, Maybe Expr) }
-  : Identifier          { ($1, Nothing) }
-  | Identifier "=" Expr { ($1, Just $3) }
+VariablePortIdentifier :: { (Identifier, Expr) }
+  : Identifier          { ($1, Nil) }
+  | Identifier "=" Expr { ($1, $3 ) }
 
 Direction :: { Direction }
   : "inout"  { Inout  }
@@ -705,8 +705,8 @@ SimpleImmediateAssertionStatement :: { Assertion }
   | "cover"  "(" Expr ")" Stmt        { Cover  (Right $3) $5 }
 
 PropertySpec :: { PropertySpec }
-  : opt(ClockingEvent) "disable" "iff" "(" Expr ")" PropExpr { PropertySpec $1 (Just $5) $7 }
-  | opt(ClockingEvent)                              PropExpr { PropertySpec $1 (Nothing) $2 }
+  : opt(ClockingEvent) "disable" "iff" "(" Expr ")" PropExpr { PropertySpec $1 $5  $7 }
+  | opt(ClockingEvent)                              PropExpr { PropertySpec $1 Nil $2 }
 
 PropExpr :: { PropExpr }
   : SeqExpr { PropExpr $1 }
@@ -752,23 +752,26 @@ AttrSpecs :: { [AttrSpec] }
   : AttrSpec               { [$1] }
   | AttrSpecs "," AttrSpec { $1 ++ [$3] }
 AttrSpec :: { AttrSpec }
-  : Identifier "=" Expr { ($1, Just $3) }
-  | Identifier          { ($1, Nothing) }
+  : Identifier "=" Expr { ($1, $3 ) }
+  | Identifier          { ($1, Nil) }
 
-NInputGates :: { [(Maybe Expr, Identifier, LHS, [Expr])] }
+NInputGates :: { [(Expr, Identifier, LHS, [Expr])] }
   : NInputGate                 { [$1] }
   | NInputGates "," NInputGate { $1 ++ [$3]}
-NOutputGates :: { [(Maybe Expr, Identifier, [LHS], Expr)] }
+NOutputGates :: { [(Expr, Identifier, [LHS], Expr)] }
   : NOutputGate                  { [$1] }
   | NOutputGates "," NOutputGate { $1 ++ [$3]}
 
-NInputGate :: { (Maybe Expr, Identifier, LHS, [Expr]) }
-  : opt(DelayControl) opt(Identifier) "(" LHS "," Exprs ")" { ($1, fromMaybe "" $2, $4, $6) }
-NOutputGate :: { (Maybe Expr, Identifier, [LHS], Expr) }
-  : opt(DelayControl) opt(Identifier) "(" NOutputGateItems { ($1, fromMaybe "" $2, fst $4, snd $4) }
+NInputGate :: { (Expr, Identifier, LHS, [Expr]) }
+  : DelayControlOrNil opt(Identifier) "(" LHS "," Exprs ")" { ($1, fromMaybe "" $2, $4, $6) }
+NOutputGate :: { (Expr, Identifier, [LHS], Expr) }
+  : DelayControlOrNil opt(Identifier) "(" NOutputGateItems { ($1, fromMaybe "" $2, fst $4, snd $4) }
 NOutputGateItems :: { ([LHS], Expr) }
   : Expr ")" { ([], $1) }
   | Expr "," NOutputGateItems { (fst $3 ++ [toLHS $1], snd $3) }
+DelayControlOrNil :: { Expr }
+  : DelayControl { $1 }
+  | {- empty -} { Nil }
 
 NInputGateKW :: { NInputGateKW }
   : "and"  { GateAnd  }
@@ -937,10 +940,10 @@ PortBindingsInside :: { [PortBinding] }
   : PortBinding                        { [$1] }
   | PortBinding "," PortBindingsInside { $1 : $3}
 PortBinding :: { PortBinding }
-  : "." Identifier "(" opt(Expr) ")" { ($2, $4) }
-  | "." Identifier                   { ($2, Just $ Ident $2) }
-  | Expr                             { ("", Just $1) }
-  | ".*"                             { ("*", Nothing) }
+  : "." Identifier "(" ExprOrNil ")" { ($2, $4) }
+  | "." Identifier                   { ($2, Ident $2) }
+  | Expr                             { ("", $1) }
+  | ".*"                             { ("*", Nil) }
 
 ParamBindings :: { [ParamBinding] }
   : "#" "("                     ")" { [] }
@@ -984,8 +987,7 @@ StmtNonBlock :: { Stmt }
   | "for" "(" ForInit ForCond ForStep ")" Stmt { For $3 $4 $5 $7 }
   | Unique CaseKW "(" Expr ")" Cases "endcase" { Case $1 $2 $4 $6 }
   | TimingControl Stmt                         { Timing $1 $2 }
-  | "return" Expr ";"                          { Return $2 }
-  | "return"      ";"                          { Return Nil }
+  | "return" ExprOrNil ";"                     { Return $2 }
   | "break"       ";"                          { Break }
   | "continue"    ";"                          { Continue }
   | "while"  "(" Expr ")" Stmt                 { While   $3 $5 }
@@ -1131,22 +1133,22 @@ Time :: { String }
 CallArgs :: { Args }
   : "(" CallArgsInside ")" { $2 }
 CallArgsInside :: { Args }
-  : {- empty -}                        { Args [            ] [] }
-  |                NamedCallArgsFollow { Args [            ] $1 }
-  | Expr                 NamedCallArgs { Args [Just $1     ] $2 }
-  |      UnnamedCallArgs NamedCallArgs { Args (Nothing : $1) $2 }
-  | Expr UnnamedCallArgs NamedCallArgs { Args (Just $1 : $2) $3 }
-UnnamedCallArgs :: { [Maybe Expr] }
-  : "," opt(Expr)                { [$2] }
-  | UnnamedCallArgs "," opt(Expr) { $1 ++ [$3] }
-NamedCallArgs :: { [(Identifier, Maybe Expr)] }
+  : {- empty -}                        { Args [        ] [] }
+  |                NamedCallArgsFollow { Args [        ] $1 }
+  | Expr                 NamedCallArgs { Args [$1      ] $2 }
+  |      UnnamedCallArgs NamedCallArgs { Args (Nil : $1) $2 }
+  | Expr UnnamedCallArgs NamedCallArgs { Args ($1  : $2) $3 }
+UnnamedCallArgs :: { [Expr] }
+  : "," ExprOrNil                 { [$2] }
+  | UnnamedCallArgs "," ExprOrNil { $1 ++ [$3] }
+NamedCallArgs :: { [(Identifier, Expr)] }
   : {- empty -}        { [] }
   | "," NamedCallArgsFollow  { $2 }
-NamedCallArgsFollow :: { [(Identifier, Maybe Expr)] }
+NamedCallArgsFollow :: { [(Identifier, Expr)] }
   : NamedCallArg                         { [$1] }
   | NamedCallArgsFollow "," NamedCallArg { $1 ++ [$3] }
-NamedCallArg :: { (Identifier, Maybe Expr) }
-  : "." Identifier "(" opt(Expr) ")" { ($2, $4) }
+NamedCallArg :: { (Identifier, Expr) }
+  : "." Identifier "(" ExprOrNil ")" { ($2, $4) }
 
 Exprs :: { [Expr] }
   :           Expr  { [$1] }
@@ -1230,6 +1232,10 @@ Expr :: { Expr }
   | "~^" Expr %prec REDUCE_OP { UniOp RedXnor $2 }
   | "^~" Expr %prec REDUCE_OP { UniOp RedXnor $2 }
 
+ExprOrNil :: { Expr }
+  : Expr        { $1 }
+  | {- empty -} { Nil }
+
 PatternItems :: { [(Identifier, Expr)] }
   : PatternNamedItems   { $1 }
   | PatternUnnamedItems { zip (repeat "") $1 }
@@ -1373,15 +1379,15 @@ combineDeclsAndStmts :: ([Decl], [Stmt]) -> ([Decl], [Stmt]) -> ([Decl], [Stmt])
 combineDeclsAndStmts (a1, b1) (a2, b2) = (a1 ++ a2, b1 ++ b2)
 
 makeInput :: Decl -> Decl
-makeInput (Variable Local t x a me) = Variable Input t x a me
-makeInput (Variable Input t x a me) = Variable Input t x a me
+makeInput (Variable Local t x a e) = Variable Input t x a e
+makeInput (Variable Input t x a e) = Variable Input t x a e
 makeInput (CommentDecl c) = CommentDecl c
 makeInput other =
   error $ "unexpected non-var or non-input decl: " ++ (show other)
 
 defaultFuncInput :: Decl -> Decl
-defaultFuncInput (Variable dir (Implicit sg rs) x a me) =
-  Variable dir t x a me
+defaultFuncInput (Variable dir (Implicit sg rs) x a e) =
+  Variable dir t x a e
   where
     t = if dir == Input || dir == Inout
       then IntegerVector TLogic sg rs
diff --git a/src/Language/SystemVerilog/Parser/ParseDecl.hs b/src/Language/SystemVerilog/Parser/ParseDecl.hs
index 8d9becf..d453fbe 100644
--- a/src/Language/SystemVerilog/Parser/ParseDecl.hs
+++ b/src/Language/SystemVerilog/Parser/ParseDecl.hs
@@ -46,7 +46,6 @@ module Language.SystemVerilog.Parser.ParseDecl
 ) where
 
 import Data.List (findIndex, findIndices, partition)
-import Data.Maybe (mapMaybe)
 
 import Language.SystemVerilog.AST
 import Language.SystemVerilog.Parser.Tokens (Position(..))
@@ -112,20 +111,20 @@ parseDTsAsPortDecls pieces =
         propagateDirections :: Direction -> [Decl] -> [Decl]
         propagateDirections dir (decl @ (Variable _ InterfaceT{} _ _ _) : decls) =
             decl : propagateDirections dir decls
-        propagateDirections lastDir (Variable currDir t x a me : decls) =
+        propagateDirections lastDir (Variable currDir t x a e : decls) =
             decl : propagateDirections dir decls
             where
-                decl = Variable dir t x a me
+                decl = Variable dir t x a e
                 dir = if currDir == Local then lastDir else currDir
         propagateDirections dir (decl : decls) =
             decl : propagateDirections dir decls
         propagateDirections _ [] = []
 
         portNames :: [Decl] -> [Identifier]
-        portNames items = mapMaybe portName items
-        portName :: Decl -> Maybe Identifier
-        portName (Variable _ _ ident _ _) = Just ident
-        portName CommentDecl{} = Nothing
+        portNames = filter (not . null) . map portName
+        portName :: Decl -> Identifier
+        portName (Variable _ _ ident _ _) = ident
+        portName CommentDecl{} = ""
         portName decl =
             error $ "unexpected non-variable port declaration: " ++ (show decl)
 
@@ -315,12 +314,12 @@ takeLHSStep _ _ = Nothing
 
 
 -- batches together separate declaration lists
-type Triplet = (Identifier, [Range], Maybe Expr)
+type Triplet = (Identifier, [Range], Expr)
 type Component = (Direction, Type, [Triplet])
 finalize :: (Position, Component) -> [Decl]
 finalize (pos, (dir, typ, trips)) =
     CommentDecl ("Trace: " ++ show pos) :
-    map (\(x, a, me) -> Variable dir typ x a me) trips
+    map (\(x, a, e) -> Variable dir typ x a e) trips
 
 
 -- internal; entrypoint of the critical portion of our parser
@@ -354,11 +353,11 @@ takeTrips l0 force =
         then ([], l0)
         else (trip : trips, l5)
     where
-        (x , l1) = takeIdent  l0
-        (a , l2) = takeRanges l1
-        (me, l3) = takeAsgn   l2
-        (_ , l4) = takeComma  l3
-        trip = (x, a, me)
+        (x, l1) = takeIdent  l0
+        (a, l2) = takeRanges l1
+        (e, l3) = takeAsgn   l2
+        (_, l4) = takeComma  l3
+        trip = (x, a, e)
         (trips, l5) = takeTrips l4 False
 
 tripLookahead :: [DeclToken] -> Bool
@@ -369,7 +368,7 @@ tripLookahead l0 =
         False
     -- if the identifier is the last token, or if it assigned a value, then we
     -- know we must have a valid triplet ahead
-    else if null l1 || asgn /= Nothing then
+    else if null l1 || asgn /= Nil then
         True
     -- if there is an ident followed by some number of ranges, and that's it,
     -- then there is a trailing declaration of an array ahead
@@ -442,12 +441,12 @@ takeRanges (token : tokens) =
 -- both for standard declarations and in `parseDTsAsDeclOrStmt`, where we're
 -- checking for an assignment statement. The other entry points disallow
 -- `AsgnOpNonBlocking`, so this doesn't liberalize the parser.
-takeAsgn :: [DeclToken] -> (Maybe Expr, [DeclToken])
+takeAsgn :: [DeclToken] -> (Expr, [DeclToken])
 takeAsgn (DTAsgn _ op Nothing e : rest) =
     if op == AsgnOpEq || op == AsgnOpNonBlocking
-        then (Just e , rest)
-        else (Nothing, rest)
-takeAsgn rest = (Nothing, rest)
+        then (e  , rest)
+        else (Nil, rest)
+takeAsgn rest = (Nil, rest)
 
 takeComma :: [DeclToken] -> (Bool, [DeclToken])
 takeComma [] = (False, [])