restrict unbased unsized bit representation

src/Convert/Cast.hs

@@ -116,16 +116,15 @@ convertCastM (RawNum size) (Number (Based 1 True Binary a b)) signed =
     return $ Number $ Based (fromIntegral size) signed Binary
         (val * a) (val * b)
     where val = (2 ^ size) - 1
-convertCastM (RawNum size) (Number (UnbasedUnsized ch)) signed =
+convertCastM (RawNum size) (Number (UnbasedUnsized bit)) signed =
     convertCastM (RawNum size) (Number num) signed
     where
         num = Based 1 True Binary a b
-        (a, b) = case ch of
-            '0' -> (0, 0)
-            '1' -> (1, 0)
-            'x' -> (0, 1)
-            'z' -> (1, 1)
-            _ -> error $ "unexpected unbased-unsized digit: " ++ [ch]
+        (a, b) = case bit of
+            Bit0 -> (0, 0)
+            Bit1 -> (1, 0)
+            BitX -> (0, 1)
+            BitZ -> (1, 1)
 convertCastM size value signed = do
     value' <- traverseExprM value
     useFn <- embedScopes canUseCastFn size

src/Convert/DimensionQuery.hs

@@ -79,7 +79,7 @@ convertExpr (DimFn f (Left t) (Number n)) =
     if isUnresolved t then
         DimFn f (Left t) (Number n)
     else if d <= 0 || d > length rs then
-        Number $ UnbasedUnsized 'x'
+        Number $ UnbasedUnsized BitX
     else case f of
         FnLeft -> fst r
         FnRight -> snd r

src/Convert/TypeOf.hs

@@ -96,9 +96,9 @@ traverseExprM (Cast (Left (Implicit sg [])) expr) =
     -- and `$unsigned` system functions present in Verilog-2005
     traverseExprM $ Call (Ident fn) $ Args [expr] []
     where fn = if sg == Signed then "$signed" else "$unsigned"
-traverseExprM (Cast (Left t) (Number (UnbasedUnsized ch))) =
+traverseExprM (Cast (Left t) (Number (UnbasedUnsized bit))) =
     -- defer until this expression becomes explicit
-    return $ Cast (Left t) (Number (UnbasedUnsized ch))
+    return $ Cast (Left t) (Number (UnbasedUnsized bit))
 traverseExprM (Cast (Left (t @ (IntegerAtom TInteger _))) expr) =
     -- convert to cast to an integer vector type
     traverseExprM $ Cast (Left t') expr

src/Convert/UnbasedUnsized.hs

@@ -68,11 +68,11 @@ convertModuleItem parts (Instance moduleName params instanceName [] bindings) =
             convertExpr (ContextDetermined tag) expr
         replaceBindingExpr :: Identifier -> Int -> Expr -> Expr
         replaceBindingExpr portName idx (orig @ (Repeat _ [ConvertedUU a b])) =
-            if orig == sizedLiteralFor tag ch
+            if orig == sizedLiteralFor tag bit
                 then Repeat portSize [ConvertedUU a b]
                 else orig
             where
-                ch = charForBit a b
+                bit = bitForBased a b
                 portName' =
                     if null portName
                         then lookupBindingName portNames idx
@@ -159,28 +159,21 @@ convertModuleItem' =
     traverseTypes (traverseNestedTypes convertType) .
     traverseAsgns convertAsgn
 
-literalFor :: Char -> Expr
-literalFor 'Z' = literalFor 'z'
-literalFor 'X' = literalFor 'x'
-literalFor '0' = Number $ Based 1 True Binary 0 0
-literalFor '1' = Number $ Based 1 True Binary 1 0
-literalFor 'x' = Number $ Based 1 True Binary 0 1
-literalFor 'z' = Number $ Based 1 True Binary 1 1
-literalFor ch = error $ "unexpected unbased-unsized digit: " ++ [ch]
+literalFor :: Bit -> Expr
+literalFor = Number . (uncurry $ Based 1 True Binary) . bitToVK
 
 pattern ConvertedUU :: Integer -> Integer -> Expr
 pattern ConvertedUU a b = Number (Based 1 True Binary a b)
 
-charForBit :: Integer -> Integer -> Char
-charForBit 0 0 = '0'
-charForBit 1 0 = '1'
-charForBit 0 1 = 'x'
-charForBit 1 1 = 'z'
-charForBit _ _ = error "charForBit invariant violated"
+bitForBased :: Integer -> Integer -> Bit
+bitForBased 0 0 = Bit0
+bitForBased 1 0 = Bit1
+bitForBased 0 1 = BitX
+bitForBased _ _ = BitZ
 
-sizedLiteralFor :: Expr -> Char -> Expr
-sizedLiteralFor expr ch =
-    Repeat size [literalFor ch]
+sizedLiteralFor :: Expr -> Bit -> Expr
+sizedLiteralFor expr bit =
+    Repeat size [literalFor bit]
     where size = DimsFn FnBits $ Right expr
 
 convertAsgn :: (LHS, Expr) -> (LHS, Expr)
@@ -251,14 +244,14 @@ convertExpr context (UniOp op expr) =
     if isSizedUniOp op
         then UniOp op (convertExpr context expr)
         else UniOp op (convertExpr SelfDetermined expr)
-convertExpr SelfDetermined (UU ch) =
-    literalFor ch
-convertExpr (ContextDetermined expr) (UU ch) =
-    sizedLiteralFor expr ch
+convertExpr SelfDetermined (UU bit) =
+    literalFor bit
+convertExpr (ContextDetermined expr) (UU bit) =
+    sizedLiteralFor expr bit
 convertExpr _ other = other
 
-pattern UU :: Char -> Expr
-pattern UU ch = Number (UnbasedUnsized ch)
+pattern UU :: Bit -> Expr
+pattern UU bit = Number (UnbasedUnsized bit)
 
 convertType :: Type -> Type
 convertType (TypeOf e) = TypeOf $ convertExpr SelfDetermined e

src/Language/SystemVerilog/AST/Number.hs

@@ -7,11 +7,13 @@
 module Language.SystemVerilog.AST.Number
     ( Number (..)
     , Base (..)
+    , Bit (..)
     , parseNumber
     , numberBitLength
     , numberIsSigned
     , numberIsSized
     , numberToInteger
+    , bitToVK
     ) where
 
 import Data.Bits (shiftL)
@@ -26,7 +28,10 @@ parseNumber = parseNumber' . map toLower . filter (not . isPad)
     where isPad = flip elem "_ \n\t"
 
 parseNumber' :: String -> Number
-parseNumber' ['\'', ch] = UnbasedUnsized ch
+parseNumber' "'0" = UnbasedUnsized Bit0
+parseNumber' "'1" = UnbasedUnsized Bit1
+parseNumber' "'x" = UnbasedUnsized BitX
+parseNumber' "'z" = UnbasedUnsized BitZ
 parseNumber' str =
     -- simple decimal number
     if maybeIdx == Nothing then
@@ -145,6 +150,26 @@ zDigits = ['z', '?']
 xzDigits :: [Char]
 xzDigits = xDigits ++ zDigits
 
+data Bit
+    = Bit0
+    | Bit1
+    | BitX
+    | BitZ
+    deriving (Eq, Ord)
+
+instance Show Bit where
+    show Bit0 = "0"
+    show Bit1 = "1"
+    show BitX = "x"
+    show BitZ = "z"
+
+-- convet an unbased unsized bit to its (values, kinds) pair
+bitToVK :: Bit -> (Integer, Integer)
+bitToVK Bit0 = (0, 0)
+bitToVK Bit1 = (1, 0)
+bitToVK BitX = (0, 1)
+bitToVK BitZ = (1, 1)
+
 data Base
     = Binary
     | Octal
@@ -157,7 +182,7 @@ instance Show Base where
     show Hex    = "h"
 
 data Number
-    = UnbasedUnsized Char
+    = UnbasedUnsized Bit
     | Decimal Int Bool Integer
     | Based   Int Bool Base Integer Integer
     deriving (Eq, Ord)
@@ -191,8 +216,8 @@ numberIsSigned (Based _ signed _ _ _) = signed
 
 -- get the integer value of a number, provided it has not X or Z bits
 numberToInteger :: Number -> Maybe Integer
-numberToInteger (UnbasedUnsized '1') = Just 1
-numberToInteger (UnbasedUnsized '0') = Just 0
+numberToInteger (UnbasedUnsized Bit1) = Just 1
+numberToInteger (UnbasedUnsized Bit0) = Just 0
 numberToInteger UnbasedUnsized{} = Nothing
 numberToInteger (Decimal _ _ num) = Just num
 numberToInteger (Based _ _ _ num 0) = Just num
@@ -205,10 +230,8 @@ bits n = 1 + bits (quot n 2)
 
 -- number to string conversion
 instance Show Number where
-    show (UnbasedUnsized ch) =
-        if elem ch "01xzXZ"
-            then ['\'', ch]
-            else error $ "illegal unbased-unsized char: " ++ show ch
+    show (UnbasedUnsized bit) =
+        '\'' : show bit
     show (Decimal (-32) True value) =
         if value < 0
             then error $ "illegal decimal: " ++ show value
@@ -326,11 +349,5 @@ instance Semigroup Number where
             toBased (n @ Based{}) = n
             toBased (Decimal size signed num) =
                 Based size signed Hex num 0
-            toBased (UnbasedUnsized ch) =
-                case ch of
-                    '0' -> based 0 0
-                    '1' -> based 1 0
-                    'x' -> based 0 1
-                    'z' -> based 1 1
-                    _ -> error $ "invalid unbased unsized char: " ++ show ch
-                where based = Based 1 False Binary
+            toBased (UnbasedUnsized bit) =
+                uncurry (Based 1 False Binary) (bitToVK bit)