v2 perplexed

app/Main.hs

@@ -0,0 +1,54 @@
+module Main where
+
+import System.Environment (getArgs)
+import System.Exit (exitFailure, exitSuccess)
+import System.IO (hPutStrLn, stderr)
+import qualified Data.ByteString.Lazy.Char8 as BL
+
+import FWL.Parser  (parseFile)
+import FWL.Pretty  (prettyProgram)
+import FWL.Check   (checkProgram)
+import FWL.Compile (compileToJson)
+
+main :: IO ()
+main = do
+  args <- getArgs
+  case args of
+    ["check",   fp] -> runCheck   fp
+    ["compile", fp] -> runCompile fp
+    ["pretty",  fp] -> runPretty  fp
+    _ -> do
+      putStrLn "Usage: fwlc <command> <file.fwl>"
+      putStrLn "  check   <file>   -- parse and static-check"
+      putStrLn "  compile <file>   -- emit nftables JSON to stdout"
+      putStrLn "  pretty  <file>   -- parse and re-print"
+      exitFailure
+
+runCheck :: FilePath -> IO ()
+runCheck fp = do
+  result <- parseFile fp
+  case result of
+    Left err -> hPutStrLn stderr ("Parse error:\n" ++ show err) >> exitFailure
+    Right prog -> do
+      let errs = checkProgram prog
+      if null errs
+        then putStrLn "OK" >> exitSuccess
+        else mapM_ (hPutStrLn stderr . show) errs >> exitFailure
+
+runCompile :: FilePath -> IO ()
+runCompile fp = do
+  result <- parseFile fp
+  case result of
+    Left err -> hPutStrLn stderr ("Parse error:\n" ++ show err) >> exitFailure
+    Right prog -> do
+      let errs = checkProgram prog
+      if null errs
+        then BL.putStrLn (compileToJson prog)
+        else mapM_ (hPutStrLn stderr . ("Check error: " ++) . show) errs >> exitFailure
+
+runPretty :: FilePath -> IO ()
+runPretty fp = do
+  result <- parseFile fp
+  case result of
+    Left err -> hPutStrLn stderr ("Parse error:\n" ++ show err) >> exitFailure
+    Right prog -> putStr (prettyProgram prog)

cabal.project

@@ -0,0 +1 @@
+packages: .

examples/router.fwl

@@ -0,0 +1,95 @@
+-- Example: home router firewall in FWL
+-- Compile with: fwlc compile examples/router.fwl
+
+interface wan  : WAN { dynamic; };
+interface lan  : LAN { cidr4 = { 10.17.1.0/24 }; };
+interface wg0  : WireGuard {};
+
+zone lan_zone = { lan, wg0 };
+
+import rfc1918 : CIDRSet from "builtin:rfc1918";
+
+let forwards : Map<(Protocol, Port), (IP, Port)> = {
+  (tcp, :8080) -> (10.17.1.10, :80),
+  (tcp, :2222) -> (10.17.1.11, :22)
+};
+
+-- WireGuard handshake detection (compiles to ct mark state machine)
+pattern WGInitiation : (UDPHeader, Bytes) =
+  (udp { length = 156 }, [0x01 _*]);
+
+pattern WGResponse : (UDPHeader, Bytes) =
+  (udp { length = 100 }, [0x02 _*]);
+
+flow WireGuardHandshake : FlowPattern =
+  WGInitiation . WGResponse within 5s;
+
+-- Block LAN clients from tunnelling out via WireGuard
+rule blockOutboundWG : Frame -> <FlowMatch, Log> Action =
+  \frame ->
+    case frame of {
+      | Frame(iif in lan_zone -> wan, IPv4(ip, UDP(udp, payload)))
+          if matches(WGInitiation, (udp, payload)) ->
+            case perform FlowMatch.check(flowOf(ip, wg), WireGuardHandshake) of {
+              | Matched -> do {
+                  perform Log.emit(Warn, "WG blocked");
+                  Drop
+                };
+              | _ -> Continue;
+            };
+      | _ -> Continue;
+    };
+
+-- Inbound to router
+policy input : Frame
+  on { hook = Input, table = Filter, priority = Filter }
+  = {
+    | _ if ct.state in { Established, Related } -> Allow;
+    | Frame(lo, _)                              -> Allow;
+    | Frame(_, IPv6(ip6, ICMPv6(_, _)))
+        if ip6.src in fe80::/10                 -> Allow;
+    | Frame(_, IPv4(_, TCP(tcp, _)))
+        if tcp.dport == :22                     -> Allow;
+    | Frame(_, IPv4(_, UDP(udp, _)))
+        if udp.dport == :51944                  -> Allow;
+    | _                                         -> Drop;
+  };
+
+-- Forwarded traffic
+policy forward : Frame
+  on { hook = Forward, table = Filter, priority = Filter }
+  = {
+    | _ if ct.state in { Established, Related }       -> Allow;
+    | frame if iif in lan_zone && oif == wan          -> blockOutboundWG(frame);
+    | _ if ct.status == DNAT                          -> Allow;
+    | Frame(iif in lan_zone -> wan, _)                -> Allow;
+    | Frame(iif in lan_zone -> lan_zone, _)           -> Allow;
+    | Frame(wan -> lan_zone, IPv4(ip, TCP(tcp, _)))
+        if (ip.dst, tcp.dport) in forwards            -> Allow;
+    | _                                               -> Drop;
+  };
+
+-- Outbound from router
+policy output : Frame
+  on { hook = Output, table = Filter, priority = Filter }
+  = {
+    | _ -> Allow;
+  };
+
+-- NAT
+policy nat_prerouting : Frame
+  on { hook = Prerouting, table = NAT, priority = DstNat }
+  = {
+    | Frame(_, IPv4(ip, _)) ->
+        if perform FIB.daddrLocal(ip.dst)
+        then DNATMap(forwards)
+        else Allow;
+    | _ -> Allow;
+  };
+
+policy nat_postrouting : Frame
+  on { hook = Postrouting, table = NAT, priority = SrcNat }
+  = {
+    | Frame(_ -> wan, IPv4(ip, _)) if ip.src in rfc1918 -> Masquerade;
+    | _ -> Allow;
+  };

fwl.cabal

@@ -0,0 +1,58 @@
+cabal-version:      3.0
+name:               fwl
+version:            0.1.0.0
+synopsis:           Firewall Language — MVP
+build-type:         Simple
+
+common shared
+  ghc-options:      -Wall
+  default-language: Haskell2010
+
+library
+  import:           shared
+  hs-source-dirs:   src
+  exposed-modules:
+      FWL.AST
+    , FWL.Lexer
+    , FWL.Parser
+    , FWL.Pretty
+    , FWL.Check
+    , FWL.Compile
+  build-depends:
+      base        >= 4.14
+    , parsec      >= 3.1
+    , aeson       >= 2.0
+    , aeson-pretty >= 0.8
+    , text        >= 1.2
+    , containers  >= 0.6
+    , mtl         >= 2.2
+    , prettyprinter >= 1.7
+    , bytestring  >= 0.11
+    , word8       >= 0.1
+
+executable fwlc
+  import:           shared
+  main-is:          Main.hs
+  hs-source-dirs:   app
+  build-depends:
+      base, fwl, text, aeson-pretty, bytestring
+
+test-suite fwl-tests
+  import:           shared
+  type:             exitcode-stdio-1.0
+  main-is:          Spec.hs
+  hs-source-dirs:   test
+  other-modules:
+      FWL.Util
+    , ParserTests
+    , CheckTests
+    , CompileTests
+  build-depends:
+      base, fwl
+    , tasty           >= 1.4
+    , tasty-hunit     >= 0.10
+    , aeson           >= 2.0
+    , aeson-pretty    >= 0.8
+    , bytestring      >= 0.11
+    , parsec          >= 3.1
+    , vector          >= 0.12

src/FWL/AST.hs

@@ -0,0 +1,233 @@
+module FWL.AST where
+
+import Data.Bits ((.&.), (.|.), shiftL, shiftR)
+import Data.Word (Word8)  -- Word8 still used for ByteElem/hex literals
+
+type Name = String
+
+-- ─── Program ────────────────────────────────────────────────────────────────
+
+data Program = Program
+  { progConfig :: Config
+  , progDecls  :: [Decl]
+  } deriving (Show)
+
+data Config = Config
+  { configTable :: String   -- default "fwl"
+  } deriving (Show)
+
+defaultConfig :: Config
+defaultConfig = Config { configTable = "fwl" }
+
+-- ─── Declarations ───────────────────────────────────────────────────────────
+
+data Decl
+  = DInterface  Name IfaceKind [IfaceProp]
+  | DZone       Name [Name]
+  | DImport     Name Type FilePath
+  | DLet        Name Type Expr
+  | DPattern    Name Type Pat
+  | DFlow       Name FlowExpr
+  | DRule       Name Type Expr
+  | DPolicy     Name Type PolicyMeta ArmBlock
+  deriving (Show)
+
+data PolicyMeta = PolicyMeta
+  { pmHook     :: Hook
+  , pmTable    :: TableName
+  , pmPriority :: Priority
+  } deriving (Show)
+
+data Hook      = HInput | HForward | HOutput | HPrerouting | HPostrouting
+  deriving (Show, Eq)
+data TableName = TFilter | TNAT
+  deriving (Show, Eq)
+-- Priority is always an integer in the nftables JSON.
+-- Named constants are resolved to their numeric values at parse time.
+newtype Priority = Priority { priorityValue :: Int }
+  deriving (Show, Eq)
+
+-- Standard nftables priority constants
+pRaw, pConnTrackDefrag, pConnTrack, pMangle, pDstNat, pFilter, pSecurity, pSrcNat :: Priority
+pRaw             = Priority (-300)
+pConnTrackDefrag = Priority (-400)
+pConnTrack       = Priority (-200)
+pMangle          = Priority (-150)
+pDstNat          = Priority (-100)
+pFilter          = Priority 0
+pSecurity        = Priority 50
+pSrcNat          = Priority 100
+
+data IfaceKind = IWan | ILan | IWireGuard | IUser Name
+  deriving (Show)
+
+data IfaceProp
+  = IPDynamic
+  | IPCidr4 [CIDR]
+  | IPCidr6 [CIDR]
+  deriving (Show)
+
+-- | A CIDR block: base address literal paired with prefix length.
+-- e.g. (LIPv4 (10,0,0,0), 8) represents 10.0.0.0/8
+type CIDR = (Literal, Int)
+
+-- ─── Patterns ───────────────────────────────────────────────────────────────
+
+data Pat
+  = PWild
+  | PVar  Name
+  | PNamed Name
+  | PCtor  Name [Pat]
+  | PRecord Name [FieldPat]
+  | PTuple [Pat]
+  | PFrame (Maybe PathPat) Pat
+  | PBytes [ByteElem]
+  deriving (Show)
+
+data FieldPat
+  = FPEq   Name Literal
+  | FPBind Name
+  | FPAs   Name Name
+  deriving (Show)
+
+data PathPat  = PathPat (Maybe EndpointPat) (Maybe EndpointPat)
+  deriving (Show)
+
+data EndpointPat
+  = EPWild
+  | EPName   Name
+  | EPMember Name Name
+  deriving (Show)
+
+data ByteElem
+  = BEHex  Word8
+  | BEWild
+  | BEWildStar
+  deriving (Show)
+
+-- ─── Flow ───────────────────────────────────────────────────────────────────
+
+data FlowExpr
+  = FAtom Name
+  | FSeq  FlowExpr FlowExpr (Maybe Duration)
+  deriving (Show)
+
+type Duration = (Int, TimeUnit)
+
+-- Fix 1: TimeUnit must derive Eq because Literal (which embeds it via
+-- LDuration) derives Eq, requiring all constituent types to also have Eq.
+data TimeUnit = Seconds | Millis | Minutes | Hours
+  deriving (Show, Eq)
+
+-- ─── Types ──────────────────────────────────────────────────────────────────
+
+data Type
+  = TName   Name [Type]
+  | TTuple  [Type]
+  | TFun    Type Type
+  | TEffect [Name] Type
+  deriving (Show)
+
+-- ─── Expressions ────────────────────────────────────────────────────────────
+
+data Expr
+  = EVar    Name
+  | EQual   [Name]
+  | ELit    Literal
+  | ELam    Name Expr
+  | EApp    Expr Expr
+  | ECase   Expr ArmBlock
+  | EIf     Expr Expr Expr
+  | EDo     [DoStmt]
+  | ELet    Name Expr Expr
+  | ETuple  [Expr]
+  | ESet    [Expr]
+  | EMap    [(Expr, Expr)]
+  | EPerform [Name] [Expr]
+  | EInfix  InfixOp Expr Expr
+  | ENot    Expr
+  deriving (Show)
+
+data InfixOp
+  = OpAnd | OpOr
+  | OpEq | OpNeq | OpLt | OpLte | OpGt | OpGte
+  | OpIn
+  | OpConcat
+  | OpThen
+  | OpBind
+  deriving (Show, Eq)
+
+data DoStmt
+  = DSBind Name Expr
+  | DSExpr Expr
+  deriving (Show)
+
+type ArmBlock = [Arm]
+data Arm = Arm Pat (Maybe Expr) Expr
+  deriving (Show)
+
+-- ─── Literals ───────────────────────────────────────────────────────────────
+
+-- IP addresses are stored as plain Integers for easy arithmetic,
+-- CIDR validation (mask host bits), and future subnet math.
+-- IPv4: 32-bit value in the low 32 bits.
+-- IPv6: 128-bit value.
+-- CIDR host-bit validation: (addr .&. hostMask prefix bits) == 0
+data IPVersion = IPv4 | IPv6
+  deriving (Show, Eq)
+
+data Literal
+  = LInt      Int
+  | LString   String
+  | LBool     Bool
+  | LIP       IPVersion Integer   -- unified IP address representation
+  | LCIDR     Literal Int         -- base address + prefix length
+  | LPort     Int
+  | LDuration Int TimeUnit
+  | LHex      Word8
+  deriving (Show, Eq)
+
+-- ─── IP address helpers ──────────────────────────────────────────────────────
+
+-- | Build an IPv4 literal from four octets.
+ipv4Lit :: Int -> Int -> Int -> Int -> Literal
+ipv4Lit a b c d =
+  LIP IPv4 (fromIntegral a `shiftL` 24
+          .|. fromIntegral b `shiftL` 16
+          .|. fromIntegral c `shiftL` 8
+          .|. fromIntegral d)
+
+-- | Check that a CIDR has no host bits set.
+cidrHostBitsZero :: Integer -> Int -> Int -> Bool
+cidrHostBitsZero addr prefix bits =
+  let hostBits = bits - prefix
+      hostMask = (1 `shiftL` hostBits) - 1
+  in  (addr .&. hostMask) == 0
+
+-- | Render an IPv4 integer as a dotted-decimal string.
+renderIPv4 :: Integer -> String
+renderIPv4 n =
+  show ((n `shiftR` 24) .&. 0xff) ++ "." ++
+  show ((n `shiftR` 16) .&. 0xff) ++ "." ++
+  show ((n `shiftR`  8) .&. 0xff) ++ "." ++
+  show  (n              .&. 0xff)
+
+-- | Render an IPv6 integer as a condensed colon-hex string.
+renderIPv6 :: Integer -> String
+renderIPv6 n =
+  let groups = [ fromIntegral ((n `shiftR` (i * 16)) .&. 0xffff) :: Int
+               | i <- [7,6..0] ]
+      hexGroups = map (`showHex` "") groups
+  in  concatIntersperse ":" hexGroups
+  where
+    showHex x s = let h = showHexInt x in h ++ s
+    showHexInt x
+      | x == 0    = "0"
+      | otherwise = reverse (go x)
+      where go 0 = []
+            go v = let (q,r) = v `divMod` 16
+                       c     = "0123456789abcdef" !! r
+                   in  c : go q
+    concatIntersperse _ []     = ""
+    concatIntersperse _ [x]    = x
+    concatIntersperse s (x:xs) = x ++ s ++ concatIntersperse s xs

src/FWL/Check.hs

@@ -0,0 +1,207 @@
+{- | Static checks for MVP:
+     1. Undefined name detection (interfaces, zones, patterns, rules/policies)
+     2. Policy arm termination: last arm of a policy must not be Continue
+     3. Named pattern cycle detection
+     4. CIDR exhaustiveness stub (warns but does not error for MVP)
+-}
+module FWL.Check
+  ( checkProgram
+  , CheckError(..)
+  ) where
+
+import Data.List (foldl', nub)
+import qualified Data.Map.Strict as Map
+import qualified Data.Set as Set
+
+import FWL.AST
+
+data CheckError
+  = UndefinedName    String String   -- kind, name
+  | PolicyNoContinue String          -- policy name
+  | PatternCycle     [String]        -- cycle path
+  | DuplicateDecl    String String   -- kind, name
+  deriving (Show, Eq)
+
+type Env = Map.Map String DeclKind
+data DeclKind = KInterface | KZone | KLet | KPattern | KFlow | KRule | KPolicy
+  deriving (Show, Eq)
+
+checkProgram :: Program -> [CheckError]
+checkProgram (Program _ decls) =
+  dupErrs ++ nameErrs ++ policyErrs ++ cycleErrs
+  where
+    env        = buildEnv decls
+    dupErrs    = findDups decls
+    nameErrs   = concatMap (checkDecl env) decls
+    policyErrs = concatMap checkPolicyTermination decls
+    cycleErrs  = checkPatternCycles decls
+
+-- ─── Environment ─────────────────────────────────────────────────────────────
+
+buildEnv :: [Decl] -> Env
+buildEnv = foldl' addDecl Map.empty
+  where
+    addDecl m (DInterface n _ _) = Map.insert n KInterface m
+    addDecl m (DZone n _)        = Map.insert n KZone m
+    addDecl m (DLet n _ _)       = Map.insert n KLet m
+    addDecl m (DPattern n _ _)   = Map.insert n KPattern m
+    addDecl m (DFlow n _)        = Map.insert n KFlow m
+    addDecl m (DRule n _ _)      = Map.insert n KRule m
+    addDecl m (DPolicy n _ _ _)  = Map.insert n KPolicy m
+    addDecl m _                  = m
+
+findDups :: [Decl] -> [CheckError]
+findDups decls = go [] Set.empty decls
+  where
+    go acc _ []     = acc
+    go acc seen (d:ds) =
+      let n = declName d in
+      if Set.member n seen
+        then go (DuplicateDecl (declKindStr d) n : acc) seen ds
+        else go acc (Set.insert n seen) ds
+
+declName :: Decl -> String
+declName (DInterface n _ _) = n
+declName (DZone n _)        = n
+declName (DImport n _ _)    = n
+declName (DLet n _ _)       = n
+declName (DPattern n _ _)   = n
+declName (DFlow n _)        = n
+declName (DRule n _ _)      = n
+declName (DPolicy n _ _ _)  = n
+
+declKindStr :: Decl -> String
+declKindStr (DInterface _ _ _) = "interface"
+declKindStr (DZone _ _)        = "zone"
+declKindStr (DImport _ _ _)    = "import"
+declKindStr (DLet _ _ _)       = "let"
+declKindStr (DPattern _ _ _)   = "pattern"
+declKindStr (DFlow _ _)        = "flow"
+declKindStr (DRule _ _ _)      = "rule"
+declKindStr (DPolicy _ _ _ _)  = "policy"
+
+-- ─── Name resolution ─────────────────────────────────────────────────────────
+
+checkDecl :: Env -> Decl -> [CheckError]
+checkDecl env (DZone _ ns)       = concatMap (checkName env "interface or zone") ns
+checkDecl env (DPattern _ _ p)   = checkPat env p
+checkDecl env (DFlow _ fe)       = checkFlow env fe
+checkDecl env (DRule _ _ e)      = checkExpr env e
+checkDecl env (DPolicy _ _ _ ab) = concatMap (checkArm env) ab
+checkDecl env (DLet _ _ e)       = checkExpr env e
+checkDecl _   _                  = []
+
+checkName :: Env -> String -> String -> [CheckError]
+checkName env kind n
+  | Map.member n env          = []
+  | isBuiltin n               = []
+  | otherwise                 = [UndefinedName kind n]
+
+isBuiltin :: String -> Bool
+isBuiltin n = n `elem`
+  [ "ct", "iif", "oif", "lo", "wan", "lan"
+  , "tcp", "udp", "ip", "ip6", "eth"
+  , "Established", "Related", "DNAT"
+  , "Allow", "Drop", "Continue", "Masquerade"
+  , "Matched", "Unmatched"
+  , "true", "false"
+  ]
+
+checkPat :: Env -> Pat -> [CheckError]
+checkPat _   PWild            = []
+checkPat _   (PVar _)         = []
+checkPat env (PNamed n)       = checkName env "pattern" n
+checkPat env (PCtor _ ps)     = concatMap (checkPat env) ps
+checkPat env (PRecord _ fs)   = concatMap (checkFP env) fs
+checkPat env (PTuple ps)      = concatMap (checkPat env) ps
+checkPat env (PFrame mp inner)= maybe [] (checkPath env) mp ++ checkPat env inner
+checkPat _   (PBytes _)       = []
+
+checkFP :: Env -> FieldPat -> [CheckError]
+checkFP _ _ = []   -- field names checked by type-checker later
+
+checkPath :: Env -> PathPat -> [CheckError]
+checkPath env (PathPat ms md) =
+  maybe [] (checkEP env) ms ++ maybe [] (checkEP env) md
+
+checkEP :: Env -> EndpointPat -> [CheckError]
+checkEP _   EPWild           = []
+checkEP env (EPName n)       = checkName env "interface or zone" n
+checkEP env (EPMember _ z)   = checkName env "zone" z
+
+checkFlow :: Env -> FlowExpr -> [CheckError]
+checkFlow env (FAtom n)      = checkName env "pattern" n
+checkFlow env (FSeq a b _)   = checkFlow env a ++ checkFlow env b
+
+checkArm :: Env -> Arm -> [CheckError]
+checkArm env (Arm p mg e) =
+  checkPat env p ++
+  maybe [] (checkExpr env) mg ++
+  checkExpr env e
+
+checkExpr :: Env -> Expr -> [CheckError]
+checkExpr env (EVar n)         = checkName env "name" n
+checkExpr _   (EQual _)        = []   -- qualified names: deferred
+checkExpr _   (ELit _)         = []
+checkExpr env (ELam _ e)       = checkExpr env e
+checkExpr env (EApp f x)       = checkExpr env f ++ checkExpr env x
+checkExpr env (ECase e ab)     = checkExpr env e ++ concatMap (checkArm env) ab
+checkExpr env (EIf c t f)      = concatMap (checkExpr env) [c,t,f]
+checkExpr env (EDo ss)         = concatMap (checkStmt env) ss
+checkExpr env (ELet _ e1 e2)   = checkExpr env e1 ++ checkExpr env e2
+checkExpr env (ETuple es)      = concatMap (checkExpr env) es
+checkExpr env (ESet es)        = concatMap (checkExpr env) es
+checkExpr env (EMap ms)        = concatMap (\(k,v) -> checkExpr env k ++ checkExpr env v) ms
+checkExpr env (EPerform _ as_) = concatMap (checkExpr env) as_
+checkExpr env (EInfix _ l r)   = checkExpr env l ++ checkExpr env r
+checkExpr env (ENot e)         = checkExpr env e
+
+checkStmt :: Env -> DoStmt -> [CheckError]
+checkStmt env (DSBind _ e) = checkExpr env e
+checkStmt env (DSExpr e)   = checkExpr env e
+
+-- ─── Policy termination ───────────────────────────────────────────────────────
+
+-- The last arm of a policy block must not unconditionally return Continue.
+checkPolicyTermination :: Decl -> [CheckError]
+checkPolicyTermination (DPolicy n _ _ arms)
+  | null arms              = [PolicyNoContinue n]
+  | isContinue (last arms) = [PolicyNoContinue n]
+  | otherwise              = []
+  where
+    isContinue (Arm PWild Nothing (EVar "Continue")) = True
+    isContinue _                                     = False
+checkPolicyTermination _ = []
+
+-- ─── Pattern cycle detection ─────────────────────────────────────────────────
+
+checkPatternCycles :: [Decl] -> [CheckError]
+checkPatternCycles decls =
+  [ PatternCycle c
+  | c <- findCycles graph
+  ]
+  where
+    patDecls = [(n, p) | DPattern n _ p <- decls]
+    graph    = Map.fromList [(n, nub (refsInPat p)) | (n,p) <- patDecls]
+    allPats  = Set.fromList (map fst patDecls)
+
+    refsInPat :: Pat -> [String]
+    refsInPat (PNamed r)     = [r | Set.member r allPats]
+    refsInPat (PCtor _ ps)   = concatMap refsInPat ps
+    refsInPat (PTuple ps)    = concatMap refsInPat ps
+    refsInPat (PFrame _ p)   = refsInPat p
+    refsInPat _              = []
+
+findCycles :: Map.Map String [String] -> [[String]]
+findCycles graph = go Set.empty Set.empty [] (Map.keys graph)
+  where
+    go _       _      _    []     = []
+    go visited onPath path (n:ns)
+      | Set.member n visited = go visited onPath path ns
+      | Set.member n onPath  = [path]
+      | otherwise =
+          let onPath' = Set.insert n onPath
+              path'   = path ++ [n]
+              deps    = Map.findWithDefault [] n graph
+              cycles  = go visited onPath' path' deps
+          in cycles ++ go (Set.insert n visited) onPath path ns

src/FWL/Compile.hs

@@ -0,0 +1,313 @@
+{-# LANGUAGE OverloadedStrings #-}
+{- | Compile a checked FWL program to nftables JSON using Aeson.
+     All policies (Filter and NAT) go into one table named by Config.
+     Layer stripping: Frame patterns that omit Ether compile identically
+     to those that include it.
+-}
+module FWL.Compile
+  ( compileProgram
+  , compileToJson
+  ) where
+
+import Data.List (intercalate)
+import Data.Maybe (mapMaybe)
+import qualified Data.Map.Strict as Map
+import Data.Aeson ((.=), Value(..), object, toJSON)
+import qualified Data.Aeson as A
+import qualified Data.Text as T
+import qualified Data.ByteString.Lazy as BL
+import Data.Aeson.Encode.Pretty (encodePretty)
+
+import FWL.AST
+
+-- ─── Entry points ────────────────────────────────────────────────────────────
+
+compileToJson :: Program -> BL.ByteString
+compileToJson = encodePretty . programToValue
+
+-- exposed for tests
+compileProgram :: Program -> Value
+compileProgram = programToValue
+
+programToValue :: Program -> Value
+programToValue (Program cfg decls) =
+  object [ "nftables" .= toJSON
+    (metainfo : tableObj : chainObjs ++ mapObjs ++ ruleObjs) ]
+  where
+    env       = buildEnv decls
+    tbl       = configTable cfg
+
+    metainfo  = object [ "metainfo" .= object
+                  [ "json_schema_version" .= (1 :: Int) ] ]
+    tableObj  = object [ "table" .= tableValue tbl ]
+
+    policies  = [ (n, pm, ab) | DPolicy n _ pm ab <- decls ]
+    chainObjs = map  (\(n, pm, _ ) -> chainDeclValue tbl n pm) policies
+    ruleObjs  = concatMap
+                  (\(n, _, ab) -> concatMap (armToRuleValues env tbl n) ab)
+                  policies
+
+    letDecls  = [ (n, t, e) | DLet n t e <- decls ]
+    mapObjs   = mapMaybe (\(n, _, e) -> letToMapValue tbl n e) letDecls
+
+-- ─── Table / Chain declarations ──────────────────────────────────────────────
+
+tableValue :: String -> Value
+tableValue tbl = object
+  [ "family" .= ("inet" :: String)
+  , "name"   .= tbl
+  ]
+
+chainDeclValue :: String -> Name -> PolicyMeta -> Value
+chainDeclValue tbl n pm = object
+  [ "chain" .= object
+      [ "family"   .= ("inet" :: String)
+      , "table"    .= tbl
+      , "name"     .= n
+      , "type"     .= chainTypeStr (pmTable pm)
+      , "hook"     .= hookStr (pmHook pm)
+      , "prio"     .= priorityInt (pmPriority pm)
+      , "policy"   .= defaultPolicyStr (pmHook pm)
+      ]
+  ]
+
+chainTypeStr :: TableName -> String
+chainTypeStr TFilter = "filter"
+chainTypeStr TNAT    = "nat"
+
+hookStr :: Hook -> String
+hookStr HInput       = "input"
+hookStr HForward     = "forward"
+hookStr HOutput      = "output"
+hookStr HPrerouting  = "prerouting"
+hookStr HPostrouting = "postrouting"
+
+-- Priority is emitted as an integer in nftables JSON.
+priorityInt :: Priority -> Int
+priorityInt = priorityValue
+
+defaultPolicyStr :: Hook -> String
+defaultPolicyStr HInput   = "drop"
+defaultPolicyStr HForward = "drop"
+defaultPolicyStr _        = "accept"
+
+-- ─── Arm → Rule objects ──────────────────────────────────────────────────────
+
+armToRuleValues :: CompileEnv -> String -> Name -> Arm -> [Value]
+armToRuleValues env tbl chain (Arm p mg body) =
+  case compileAction env body of
+    Nothing      -> []
+    Just verdict ->
+      let patExprs   = compilePat env p
+          guardExprs = maybe [] (compileGuard env) mg
+          allExprs   = patExprs ++ guardExprs ++ [verdict]
+      in  [ object
+              [ "rule" .= object
+                  [ "family" .= ("inet" :: String)
+                  , "table"  .= tbl
+                  , "chain"  .= chain
+                  , "expr"   .= toJSON allExprs
+                  ]
+              ]
+          ]
+
+-- ─── Pattern → [Value] ───────────────────────────────────────────────────────
+
+type CompileEnv = Map.Map String Decl
+
+buildEnv :: [Decl] -> CompileEnv
+buildEnv = foldr (\d m -> Map.insert (declNameOf d) d m) Map.empty
+  where
+    declNameOf (DInterface n _ _) = n
+    declNameOf (DZone n _)        = n
+    declNameOf (DPattern n _ _)   = n
+    declNameOf (DFlow n _)        = n
+    declNameOf (DRule n _ _)      = n
+    declNameOf (DPolicy n _ _ _)  = n
+    declNameOf (DLet n _ _)       = n
+    declNameOf (DImport n _ _)    = n
+
+compilePat :: CompileEnv -> Pat -> [Value]
+compilePat _   PWild             = []
+compilePat _   (PVar _)          = []
+compilePat env (PNamed n)        = expandNamedPat env n
+compilePat env (PFrame mp inner) =
+  maybe [] (compilePathPat env) mp ++ compilePat env inner
+compilePat env (PCtor n ps)      = compileCtorPat env n ps
+compilePat _   (PRecord n fs)    = compileRecordPat n fs
+compilePat env (PTuple ps)       = concatMap (compilePat env) ps
+compilePat _   (PBytes _)        = []
+
+expandNamedPat :: CompileEnv -> Name -> [Value]
+expandNamedPat env n =
+  case Map.lookup n env of
+    Just (DPattern _ _ p) -> compilePat env p
+    _                     -> []
+
+compileCtorPat :: CompileEnv -> String -> [Pat] -> [Value]
+compileCtorPat env ctor ps = case ctor of
+  "Ether"  -> children
+  "IPv4"   -> matchMeta "nfproto" "ipv4"              : children
+  "IPv6"   -> matchMeta "nfproto" "ipv6"              : children
+  "TCP"    -> matchPayload "th"  "protocol" "tcp"     : children
+  "UDP"    -> matchPayload "th"  "protocol" "udp"     : children
+  "ICMPv6" -> matchPayload "ip6" "nexthdr"  "ipv6-icmp" : children
+  "ICMP"   -> matchPayload "ip"  "protocol" "icmp"    : children
+  _        -> children
+  where
+    children = concatMap (compilePat env) ps
+
+compileRecordPat :: String -> [FieldPat] -> [Value]
+compileRecordPat proto = mapMaybe go
+  where
+    go (FPEq field lit) = Just (matchPayload proto field (renderLit lit))
+    go _                = Nothing
+
+compilePathPat :: CompileEnv -> PathPat -> [Value]
+compilePathPat _ (PathPat ms md) =
+  maybe [] (compileEndpoint "iifname") ms ++
+  maybe [] (compileEndpoint "oifname") md
+
+compileEndpoint :: String -> EndpointPat -> [Value]
+compileEndpoint _   EPWild          = []
+compileEndpoint dir (EPName n)      = [matchMeta dir n]
+compileEndpoint dir (EPMember _ z)  = [matchInSet (metaVal dir) [z]]
+
+-- ─── Guard → [Value] ─────────────────────────────────────────────────────────
+
+compileGuard :: CompileEnv -> Expr -> [Value]
+compileGuard env (EInfix OpAnd l r)  = compileGuard env l ++ compileGuard env r
+compileGuard _   (EInfix OpIn  l r)  = [compileInExpr l r]
+compileGuard _   (EInfix OpEq  l r)  = [matchExpr "==" (exprVal l) (exprVal r)]
+compileGuard _   (EInfix OpNeq l r)  = [matchExpr "!=" (exprVal l) (exprVal r)]
+compileGuard _   _                   = []
+
+compileInExpr :: Expr -> Expr -> Value
+-- Fix 4: put the more-specific ct patterns BEFORE the generic 2-element
+-- EQual case to eliminate the overlapping pattern match warning.
+compileInExpr (EQual ["ct", "state"])  (ESet vs) = ctMatch "state"  vs
+compileInExpr (EQual ["ct", "status"]) (ESet vs) = ctMatch "status" vs
+compileInExpr l                        (ESet vs)  =
+  matchExpr "in" (exprVal l) (setVal (map exprToStr vs))
+compileInExpr l                        r          =
+  matchExpr "==" (exprVal l) (exprVal r)
+
+ctMatch :: String -> [Expr] -> Value
+ctMatch key vs = matchExpr "in"
+  (object ["ct" .= object ["key" .= (key :: String)]])
+  (setVal (map exprToStr vs))
+
+-- ─── Action → Maybe Value ─────────────────────────────────────────────────────
+
+compileAction :: CompileEnv -> Expr -> Maybe Value
+compileAction _   (EVar "Allow")      = Just (object ["accept"     .= Null])
+compileAction _   (EVar "Drop")       = Just (object ["drop"       .= Null])
+compileAction _   (EVar "Continue")   = Nothing
+compileAction _   (EVar "Masquerade") = Just (object ["masquerade" .= Null])
+compileAction _   (EApp (EVar "DNAT") arg) =
+  Just $ object ["dnat" .= object ["addr" .= exprToStr arg]]
+compileAction _   (EApp (EVar "DNATMap") arg) =
+  Just $ object ["dnat" .= object ["addr" .= object
+    [ "map"  .= object [ "key"  .= object ["concat" .= Array mempty]
+                       , "data" .= exprToStr arg ]]]]
+compileAction env (EApp (EVar rn) _) =
+  case Map.lookup rn env of
+    Just (DRule _ _ _) -> Just $ object ["jump" .= object ["target" .= rn]]
+    _                  -> Just (object ["accept" .= Null])
+compileAction _ _ = Just (object ["accept" .= Null])
+
+-- ─── Let → Map object ────────────────────────────────────────────────────────
+
+letToMapValue :: String -> Name -> Expr -> Maybe Value
+letToMapValue tbl n (EMap entries) = Just $ object
+  [ "map" .= object
+      [ "family" .= ("inet" :: String)
+      , "table"  .= tbl
+      , "name"   .= n
+      , "type"   .= ("inetproto . inetservice" :: String)
+      , "map"    .= ("ipv4_addr . inetservice" :: String)
+      , "elem"   .= toJSON (map renderMapElem entries)
+      ]
+  ]
+letToMapValue _ _ _ = Nothing
+
+renderMapElem :: (Expr, Expr) -> Value
+renderMapElem (k, v) = toJSON
+  [ object ["concat" .= toJSON [exprToStr k]]
+  , A.String (toText (exprToStr v))
+  ]
+
+-- ─── Aeson building blocks ───────────────────────────────────────────────────
+
+matchExpr :: String -> Value -> Value -> Value
+matchExpr op l r = object
+  [ "match" .= object
+      [ "op"    .= (op :: String)
+      , "left"  .= l
+      , "right" .= r
+      ]
+  ]
+
+matchMeta :: String -> String -> Value
+matchMeta key val = matchExpr "==" (metaVal key) (A.String (toText val))
+
+matchPayload :: String -> String -> String -> Value
+matchPayload proto field val =
+  matchExpr "==" (payloadVal proto field) (A.String (toText val))
+
+matchInSet :: Value -> [String] -> Value
+matchInSet lhs vals = matchExpr "in" lhs (setVal vals)
+
+metaVal :: String -> Value
+metaVal key = object ["meta" .= object ["key" .= (key :: String)]]
+
+payloadVal :: String -> String -> Value
+payloadVal proto field =
+  object ["payload" .= object
+    [ "protocol" .= (proto :: String)
+    , "field"    .= (field :: String)
+    ]]
+
+setVal :: [String] -> Value
+setVal vs = object ["set" .= toJSON vs]
+
+-- ─── Expression helpers ───────────────────────────────────────────────────────
+
+-- Fix 3 (overlap): specific ct pattern first, generic 2-element case second.
+exprVal :: Expr -> Value
+exprVal (EQual ["ct", k])  = object ["ct" .= object ["key" .= (k :: String)]]
+exprVal (EQual [p, f])     = payloadVal p f
+exprVal (EQual ns)         = A.String (toText (intercalate "." ns))
+exprVal (EVar n)           = metaVal n
+exprVal (ELit l)           = A.String (toText (renderLit l))
+exprVal (ESet vs)          = setVal (map exprToStr vs)
+exprVal e                  = A.String (toText (exprToStr e))
+
+exprToStr :: Expr -> String
+exprToStr (EVar n)    = n
+exprToStr (ELit l)    = renderLit l
+exprToStr (EQual ns)  = intercalate "." ns
+exprToStr (ETuple es) = intercalate " . " (map exprToStr es)
+exprToStr _           = "_"
+
+-- Fix 2: Use Data.Text.pack via OverloadedStrings + fromString instead of
+-- the fragile read(show s) hack. With OverloadedStrings enabled, string
+-- literals already produce the correct Text/Key types; for runtime String
+toText :: String -> T.Text
+toText = T.pack
+
+renderLit :: Literal -> String
+renderLit (LInt n)              = show n
+renderLit (LString s)           = s
+renderLit (LBool True)          = "true"
+renderLit (LBool False)         = "false"
+renderLit (LIPv4 (a, b, c, d))  =
+  show a ++ "." ++ show b ++ "." ++ show c ++ "." ++ show d
+renderLit (LIPv6 _)             = "::1"
+renderLit (LCIDR ip p)          = renderLit ip ++ "/" ++ show p
+renderLit (LPort p)             = show p
+renderLit (LDuration n Seconds) = show n ++ "s"
+renderLit (LDuration n Millis)  = show n ++ "ms"
+renderLit (LDuration n Minutes) = show n ++ "m"
+renderLit (LDuration n Hours)   = show n ++ "h"
+renderLit (LHex b)              = show b

src/FWL/Lexer.hs

@@ -0,0 +1,101 @@
+module FWL.Lexer where
+
+import Text.Parsec
+import Text.Parsec.String (Parser)
+import qualified Text.Parsec.Token as Tok
+import Text.Parsec.Language (emptyDef)
+
+-- ─── Language definition ─────────────────────────────────────────────────────
+
+fwlDef :: Tok.LanguageDef ()
+fwlDef = emptyDef
+  { Tok.commentLine     = "--"
+  , Tok.commentStart    = "{-"
+  , Tok.commentEnd      = "-}"
+  , Tok.identStart      = letter <|> char '_'
+  , Tok.identLetter     = alphaNum <|> char '_'
+  , Tok.reservedNames   =
+      -- Only genuine syntactic keywords belong here.
+      -- Semantic values used as constructors, actions, type names, or
+      -- pattern references (Allow, Drop, Log, Matched, Frame, etc.) must
+      -- NOT be reserved so that `identifier` can consume them in those
+      -- positions.
+      [ "config", "table"
+      , "interface", "zone", "import", "from"
+      , "let", "in", "pattern", "flow", "rule", "policy", "on"
+      , "case", "of", "if", "then", "else", "do", "perform"
+      , "within", "as", "dynamic", "cidr4", "cidr6"
+      , "hook", "priority"
+      , "WAN", "LAN", "WireGuard"
+      , "Input", "Forward", "Output", "Prerouting", "Postrouting"
+      , "Filter", "NAT", "Mangle", "DstNat", "SrcNat", "Raw", "ConnTrack"
+      , "true", "false"
+      ]
+  , Tok.reservedOpNames =
+      [ "->", "<-", "=>", "::", ":", "=", ".", ".."
+      , "\\", "|", ","
+      , "&&", "||", "!", "=="  , "!=", "<", "<=", ">", ">="
+      , "++", ">>", ">>="
+      , "∈"
+      ]
+  , Tok.caseSensitive   = True
+  }
+
+lexer :: Tok.TokenParser ()
+lexer = Tok.makeTokenParser fwlDef
+
+-- ─── Token helpers ───────────────────────────────────────────────────────────
+
+identifier  :: Parser String
+identifier  = Tok.identifier lexer
+
+reserved    :: String -> Parser ()
+reserved    = Tok.reserved lexer
+
+reservedOp  :: String -> Parser ()
+reservedOp  = Tok.reservedOp lexer
+
+symbol      :: String -> Parser String
+symbol      = Tok.symbol lexer
+
+parens      :: Parser a -> Parser a
+parens      = Tok.parens lexer
+
+braces      :: Parser a -> Parser a
+braces      = Tok.braces lexer
+
+angles      :: Parser a -> Parser a
+angles      = Tok.angles lexer
+
+brackets    :: Parser a -> Parser a
+brackets    = Tok.brackets lexer
+
+semi        :: Parser String
+semi        = Tok.semi lexer
+
+comma       :: Parser String
+comma       = Tok.comma lexer
+
+colon       :: Parser String
+colon       = Tok.colon lexer
+
+dot         :: Parser String
+dot         = Tok.dot lexer
+
+whiteSpace  :: Parser ()
+whiteSpace  = Tok.whiteSpace lexer
+
+stringLit   :: Parser String
+stringLit   = Tok.stringLiteral lexer
+
+natural     :: Parser Integer
+natural     = Tok.natural lexer
+
+commaSep    :: Parser a -> Parser [a]
+commaSep    = Tok.commaSep lexer
+
+commaSep1   :: Parser a -> Parser [a]
+commaSep1   = Tok.commaSep1 lexer
+
+semiSep     :: Parser a -> Parser [a]
+semiSep     = Tok.semiSep lexer

src/FWL/Parser.hs

@@ -0,0 +1,659 @@
+module FWL.Parser
+  ( parseProgram
+  , parseFile
+  ) where
+
+import Control.Monad (void)
+import Data.Bits ((.&.), (.|.), shiftL)
+import Data.List (foldl')
+import Data.Word (Word8)
+import Numeric (readHex)
+import Text.Parsec
+import Text.Parsec.String (Parser)
+import Data.Functor.Identity (Identity)
+import qualified Text.Parsec.Expr as Ex
+
+import FWL.AST
+import FWL.Lexer
+
+-- ─── Entry points ────────────────────────────────────────────────────────────
+
+parseProgram :: String -> String -> Either ParseError Program
+parseProgram src input = parse program src input
+
+parseFile :: FilePath -> IO (Either ParseError Program)
+parseFile fp = parseProgram fp <$> readFile fp
+
+-- ─── Top-level ───────────────────────────────────────────────────────────────
+
+program :: Parser Program
+program = do
+  whiteSpace
+  cfg  <- option defaultConfig configBlock
+  ds   <- many decl
+  eof
+  return (Program cfg ds)
+
+configBlock :: Parser Config
+configBlock = do
+  reserved "config"
+  props <- braces (semiSep configProp)
+  optional semi
+  return $ foldr applyProp defaultConfig props
+  where
+    applyProp ("table", v) c = c { configTable = v }
+    applyProp _            c = c
+
+configProp :: Parser (String, String)
+configProp = do
+  reserved "table"
+  reservedOp "="
+  v <- stringLit
+  return ("table", v)
+
+-- ─── Declarations ────────────────────────────────────────────────────────────
+
+decl :: Parser Decl
+decl =  interfaceDecl
+    <|> zoneDecl
+    <|> importDecl
+    <|> letDecl
+    <|> patternDecl
+    <|> flowDecl
+    <|> ruleDecl
+    <|> policyDecl
+
+interfaceDecl :: Parser Decl
+interfaceDecl = do
+  reserved "interface"
+  n  <- identifier
+  reservedOp ":"
+  k  <- ifaceKind
+  ps <- braces (endBy ifaceProp semi)
+  _ <- semi
+  return (DInterface n k ps)
+
+ifaceKind :: Parser IfaceKind
+ifaceKind =  (reserved "WAN"       >> return IWan)
+         <|> (reserved "LAN"       >> return ILan)
+         <|> (reserved "WireGuard" >> return IWireGuard)
+         <|> (IUser <$> identifier)
+
+ifaceProp :: Parser IfaceProp
+ifaceProp =  (reserved "dynamic" >> return IPDynamic)
+         <|> (reserved "cidr4" >> reservedOp "=" >> IPCidr4 <$> cidrSet)
+         <|> (reserved "cidr6" >> reservedOp "=" >> IPCidr6 <$> cidrSet)
+
+cidrSet :: Parser [CIDR]
+cidrSet = braces (commaSep1 cidrLit)
+
+zoneDecl :: Parser Decl
+zoneDecl = do
+  reserved "zone"
+  n  <- identifier
+  reservedOp "="
+  ns <- braces (commaSep1 identifier)
+  _ <- semi
+  return (DZone n ns)
+
+importDecl :: Parser Decl
+importDecl = do
+  reserved "import"
+  n <- identifier
+  reservedOp ":"
+  t <- typeP
+  reserved "from"
+  s <- stringLit
+  _ <- semi
+  return (DImport n t s)
+
+letDecl :: Parser Decl
+letDecl = do
+  reserved "let"
+  n <- identifier
+  reservedOp ":"
+  t <- typeP
+  reservedOp "="
+  e <- expr
+  _ <- semi
+  return (DLet n t e)
+
+patternDecl :: Parser Decl
+patternDecl = do
+  reserved "pattern"
+  n <- identifier
+  reservedOp ":"
+  t <- typeP
+  reservedOp "="
+  p <- pat
+  _ <- semi
+  return (DPattern n t p)
+
+flowDecl :: Parser Decl
+flowDecl = do
+  reserved "flow"
+  n <- identifier
+  reservedOp ":"
+  reserved "FlowPattern"
+  reservedOp "="
+  f <- flowExpr
+  _ <- semi
+  return (DFlow n f)
+
+ruleDecl :: Parser Decl
+ruleDecl = do
+  reserved "rule"
+  n <- identifier
+  reservedOp ":"
+  t <- typeP
+  reservedOp "="
+  e <- expr
+  _ <- semi
+  return (DRule n t e)
+
+policyDecl :: Parser Decl
+policyDecl = do
+  reserved "policy"
+  n  <- identifier
+  reservedOp ":"
+  t  <- typeP
+  reserved "on"
+  pm <- braces policyMeta
+  reservedOp "="
+  ab <- armBlock
+  _ <- semi
+  return (DPolicy n t pm ab)
+
+policyMeta :: Parser PolicyMeta
+policyMeta = do
+  props <- commaSep1 metaProp
+  let h  = foldr (\p a -> case p of Left  v -> v; _ -> a) HInput  props
+      tb = foldr (\p a -> case p of Right (Left  v) -> v; _ -> a) TFilter props
+      pr = foldr (\p a -> case p of Right (Right v) -> v; _ -> a) pFilter props
+  return (PolicyMeta h tb pr)
+
+metaProp :: Parser (Either Hook (Either TableName Priority))
+metaProp
+  =  (reserved "hook"     >> reservedOp "=" >> fmap (Left)             hookP)
+ <|> (reserved "table"    >> reservedOp "=" >> fmap (Right . Left)     tableNameP)
+ <|> (reserved "priority" >> reservedOp "=" >> fmap (Right . Right)    priorityP)
+
+hookP :: Parser Hook
+hookP =  (reserved "Input"       >> return HInput)
+     <|> (reserved "Forward"     >> return HForward)
+     <|> (reserved "Output"      >> return HOutput)
+     <|> (reserved "Prerouting"  >> return HPrerouting)
+     <|> (reserved "Postrouting" >> return HPostrouting)
+
+tableNameP :: Parser TableName
+tableNameP =  (reserved "Filter" >> return TFilter)
+          <|> (reserved "NAT"    >> return TNAT)
+
+priorityP :: Parser Priority
+priorityP
+  =  (reserved "Filter"  >> return pFilter)
+ <|> (reserved "DstNat"  >> return pDstNat)
+ <|> (reserved "SrcNat"  >> return pSrcNat)
+ <|> (reserved "Mangle"  >> return pMangle)
+ <|> (reserved "Raw"     >> return pRaw)
+ <|> (reserved "ConnTrack" >> return pConnTrack)
+ <|> (Priority . fromIntegral <$> integerP)
+  where
+    -- Accept optional leading minus for negative priorities
+    integerP = do
+      neg <- option 1 (char '-' >> return (-1))
+      n   <- natural
+      whiteSpace
+      return (neg * fromIntegral n)
+
+-- ─── Arm blocks ──────────────────────────────────────────────────────────────
+
+armBlock :: Parser ArmBlock
+armBlock = braces (many arm)
+
+arm :: Parser Arm
+arm = do
+  _ <- symbol "|"
+  p  <- pat
+  g  <- optionMaybe (reserved "if" >> expr)
+  reservedOp "->"
+  e  <- expr
+  _ <- semi
+  return (Arm p g e)
+
+-- ─── Patterns ────────────────────────────────────────────────────────────────
+
+pat :: Parser Pat
+pat =  wildcardPat
+   <|> try framePat
+   <|> try tuplePat
+   <|> bytesPat
+   <|> try recordPat
+   <|> try namedOrCtorPat
+
+wildcardPat :: Parser Pat
+wildcardPat = symbol "_" >> return PWild
+
+-- Frame(...) — optional path then inner pattern
+-- Layer stripping: if the inner pattern is not Ether/IPv4/IPv6/etc the
+-- type-checker will peel outer layers automatically. Parser just stores
+-- whatever the user wrote.
+framePat :: Parser Pat
+framePat = do
+  reserved "Frame"
+  (mp, inner) <- parens frameArgs
+  return (PFrame mp inner)
+
+frameArgs :: Parser (Maybe PathPat, Pat)
+frameArgs = try withPath <|> withoutPath
+  where
+    withPath = do
+      pp <- pathPat
+      _ <- comma
+      inner <- pat
+      return (Just pp, inner)
+    withoutPath = do
+      inner <- pat
+      return (Nothing, inner)
+
+pathPat :: Parser PathPat
+pathPat = do
+  src <- optionMaybe (try endpointPat)
+  dst <- optionMaybe (try (reservedOp "->" >> endpointPat))
+  case (src, dst) of
+    (Nothing, Nothing) -> fail "empty path pattern"
+    _                  -> return (PathPat src dst)
+
+endpointPat :: Parser EndpointPat
+endpointPat
+  =  (symbol "_" >> return EPWild)
+ <|> try (do n <- identifier
+             memberOp
+             z <- identifier
+             return (EPMember n z))
+ <|> (EPName <$> identifier)
+
+memberOp :: Parser ()
+memberOp = (reservedOp "∈" <|> reserved "in") >> return ()
+
+tuplePat :: Parser Pat
+tuplePat = do
+  ps <- parens (commaSep2 pat)
+  return (PTuple ps)
+
+commaSep2 :: Parser a -> Parser [a]
+commaSep2 p = do
+  x  <- p
+  _ <- comma
+  xs <- commaSep1 p
+  return (x:xs)
+
+bytesPat :: Parser Pat
+bytesPat = brackets (PBytes <$> many byteElem)
+
+byteElem :: Parser ByteElem
+byteElem
+  =  try (symbol "_*" >> return BEWildStar)
+ <|> try (symbol "_"  >> return BEWild)
+ <|> (BEHex <$> hexByte)
+
+hexByte :: Parser Word8
+hexByte = do
+  void (string "0x")
+  h1 <- hexDigit
+  h2 <- hexDigit
+  whiteSpace
+  case (readHex [h1,h2] :: [(Integer, String)]) of
+    [(v,"")] -> return (fromIntegral v)
+    _        -> fail "invalid hex byte"
+
+-- Record pattern: ident { fields }
+recordPat :: Parser Pat
+recordPat = do
+  n  <- identifier
+  fs <- braces (commaSep fieldPat)
+  return (PRecord n fs)
+
+fieldPat :: Parser FieldPat
+fieldPat = do
+  n <- identifier
+  try (reservedOp "=" >> FPEq n <$> fieldLiteral)
+    <|> try (reserved "as" >> FPAs n <$> identifier)
+    <|> return (FPBind n)
+
+-- Port literals (:22) are valid in record field position as well as plain literals.
+fieldLiteral :: Parser Literal
+fieldLiteral = try portLit <|> literal
+  where
+    portLit = do
+      void (char ':')
+      n <- fromIntegral <$> natural
+      return (LPort n)
+
+-- Named pattern reference OR constructor: starts with uppercase-ish ident
+namedOrCtorPat :: Parser Pat
+namedOrCtorPat = do
+  n  <- identifier
+  args <- optionMaybe (try (parens (commaSep pat)))
+  case args of
+    Nothing -> return (PNamed n)   -- bare name = named pattern ref
+    Just ps -> return (PCtor  n ps)
+
+-- ─── Flow expressions ────────────────────────────────────────────────────────
+
+flowExpr :: Parser FlowExpr
+flowExpr = do
+  first <- FAtom <$> identifier
+  rest  <- many (reservedOp "." >> identifier)
+  mw    <- optionMaybe (reserved "within" >> durationLit)
+  return $ buildSeq (first : map FAtom rest) mw
+  where
+    buildSeq [x]    mw = case mw of
+                           Nothing -> x
+                           Just w  -> FSeq x x (Just w)  -- degenerate
+    buildSeq (x:xs) mw = FSeq x (buildSeq xs mw) mw
+    buildSeq []     _  = error "impossible"
+
+durationLit :: Parser Duration
+durationLit = do
+  n <- fromIntegral <$> natural
+  u <-  (char 's' >> return Seconds)
+    <|> (string "ms" >> return Millis)
+    <|> (char 'm' >> return Minutes)
+    <|> (char 'h' >> return Hours)
+  whiteSpace
+  return (n, u)
+
+-- ─── Types ───────────────────────────────────────────────────────────────────
+
+typeP :: Parser Type
+typeP = do
+  t <- baseType
+  option t (reservedOp "->" >> TFun t <$> typeP)
+
+baseType :: Parser Type
+baseType
+  =  effectType
+ <|> try tupleTy
+ <|> simpleTy
+
+effectType :: Parser Type
+effectType = do
+  effs <- angles (commaSep identifier)
+  t    <- simpleTy
+  return (TEffect effs t)
+
+tupleTy :: Parser Type
+tupleTy = TTuple <$> parens (commaSep2 typeP)
+
+simpleTy :: Parser Type
+simpleTy = do
+  n    <- identifier
+  args <- option [] (angles (commaSep typeP))
+  return (TName n args)
+
+-- ─── Expressions ─────────────────────────────────────────────────────────────
+
+expr :: Parser Expr
+expr =  lamExpr
+    <|> ifExpr
+    <|> doExpr
+    <|> caseExpr
+    <|> letExpr
+    <|> infixExpr
+
+lamExpr :: Parser Expr
+lamExpr = do
+  reservedOp "\\"
+  n <- identifier
+  reservedOp "->"
+  e <- expr
+  return (ELam n e)
+
+ifExpr :: Parser Expr
+ifExpr = do
+  reserved "if"
+  c <- expr
+  reserved "then"
+  t <- expr
+  reserved "else"
+  f <- expr
+  return (EIf c t f)
+
+doExpr :: Parser Expr
+doExpr = reserved "do" >> braces (EDo <$> semiSep doStmt)
+
+doStmt :: Parser DoStmt
+doStmt = try bindStmt <|> (DSExpr <$> expr)
+
+bindStmt :: Parser DoStmt
+bindStmt = do
+  n <- identifier
+  reservedOp "<-"
+  e <- expr
+  return (DSBind n e)
+
+caseExpr :: Parser Expr
+caseExpr = do
+  reserved "case"
+  e  <- expr
+  reserved "of"
+  ab <- armBlock
+  return (ECase e ab)
+
+letExpr :: Parser Expr
+letExpr = do
+  reserved "let"
+  n <- identifier
+  reservedOp "="
+  e1 <- expr
+  reserved "in"
+  e2 <- expr
+  return (ELet n e1 e2)
+
+-- Operator table for infix expressions
+infixExpr :: Parser Expr
+infixExpr = Ex.buildExpressionParser opTable appExpr
+
+opTable :: Ex.OperatorTable String () Identity Expr
+opTable =
+  [ [ prefix "!" ENot ]
+  , [ infixL "==" OpEq, infixL "!=" OpNeq
+    , infixL "<"  OpLt, infixL "<=" OpLte
+    , infixL ">"  OpGt, infixL ">=" OpGte
+    , infixIn ]
+  , [ infixR "&&" OpAnd ]
+  , [ infixR "||" OpOr  ]
+  , [ infixR "++" OpConcat ]
+  , [ infixL ">>=" OpBind ]
+  , [ infixL ">>"  OpThen ]
+  ]
+  where
+    prefix op f = Ex.Prefix  (reservedOp op >> return f)
+    infixL op c = Ex.Infix   (reservedOp op >> return (EInfix c)) Ex.AssocLeft
+    infixR op c = Ex.Infix   (reservedOp op >> return (EInfix c)) Ex.AssocRight
+    infixIn     = Ex.Infix
+      ((memberOp <|> reserved "in") >> return (EInfix OpIn))
+      Ex.AssocNone
+
+appExpr :: Parser Expr
+appExpr = do
+  f    <- atom
+  args <- many atom
+  return (foldl EApp f args)
+
+atom :: Parser Expr
+atom
+  =  try performExpr
+ <|> try mapLit
+ <|> try setLit
+ <|> try tupleLit
+ <|> try (parens expr)
+ <|> try litExpr
+ <|> try portExpr
+ <|> qualNameExpr
+
+performExpr :: Parser Expr
+performExpr = do
+  reserved "perform"
+  parts <- sepBy1 identifier dot
+  args  <- parens (commaSep expr)
+  return (EPerform parts args)
+
+qualNameExpr :: Parser Expr
+qualNameExpr = do
+  parts <- sepBy1 identifier (try (dot <* notFollowedBy digit))
+  case parts of
+    [n] -> return (EVar n)
+    ns  -> return (EQual ns)
+
+litExpr :: Parser Expr
+litExpr = ELit <$> literal
+
+portExpr :: Parser Expr
+portExpr = do
+  void (char ':')
+  n <- fromIntegral <$> natural
+  return (ELit (LPort n))
+
+tupleLit :: Parser Expr
+tupleLit = ETuple <$> parens (commaSep2 expr)
+
+setLit :: Parser Expr
+setLit = braces $ do
+  items <- commaSep expr
+  return (ESet items)
+
+-- map literal: { expr -> expr, ... }
+mapLit :: Parser Expr
+mapLit = braces $ do
+  entries <- commaSep1 mapEntry
+  return (EMap entries)
+
+mapEntry :: Parser (Expr, Expr)
+mapEntry = do
+  k <- expr
+  reservedOp "->"
+  v <- expr
+  return (k, v)
+
+-- ─── Literals ────────────────────────────────────────────────────────────────
+
+literal :: Parser Literal
+literal
+  =  try ipOrCidrLit
+ <|> try hexLit
+ <|> try (LBool True  <$ reserved "true")
+ <|> try (LBool False <$ reserved "false")
+ <|> try (LString <$> stringLit)
+ <|> try (LInt . fromIntegral <$> natural)
+
+hexLit :: Parser Literal
+hexLit = LHex <$> hexByte
+
+-- ─── IP / CIDR parsing ───────────────────────────────────────────────────────
+
+-- | Parse an IPv4 or IPv6 address, optionally followed by /prefix.
+-- Tries IPv6 first (it can start with hex digits too), then IPv4.
+ipOrCidrLit :: Parser Literal
+ipOrCidrLit = do
+  ip <- try ipv6Lit <|> ipv4Lit_
+  mPrefix <- optionMaybe (char '/' >> fromIntegral <$> natural)
+  whiteSpace
+  return $ case mPrefix of
+    Nothing -> ip
+    Just p  -> LCIDR ip p
+
+-- | IPv4: four decimal octets separated by dots → LIP IPv4 (32-bit Integer)
+ipv4Lit_ :: Parser Literal
+ipv4Lit_ = do
+  a <- octet
+  void (char '.')
+  b <- octet
+  void (char '.')
+  c <- octet
+  void (char '.')
+  d <- octet
+  return $ LIP IPv4
+    (  fromIntegral a `shiftL` 24
+   .|. fromIntegral b `shiftL` 16
+   .|. fromIntegral c `shiftL` 8
+   .|. fromIntegral d)
+  where
+    octet = do
+      n <- fromIntegral <$> natural
+      if n > 255 then fail "octet out of range" else return n
+
+-- | IPv6: full notation, :: abbreviation, and optional embedded IPv4.
+-- Stores as LIP IPv6 (128-bit Integer).
+ipv6Lit :: Parser Literal
+ipv6Lit = do
+  (left, right) <- ipv6Groups
+  let missing   = 8 - length left - length right
+  when (missing < 0) $ fail "too many groups in IPv6 address"
+  let groups    = left ++ replicate missing 0 ++ right
+  when (length groups /= 8) $ fail "invalid IPv6 address"
+  let val = foldl' (\acc g -> (acc `shiftL` 16) .|. fromIntegral g) (0::Integer) groups
+  return (LIP IPv6 val)
+
+-- Returns (left-of-::, right-of-::).
+-- If no :: present, left has all 8 groups and right is empty.
+ipv6Groups :: Parser ([Int], [Int])
+ipv6Groups = do
+  -- must start with a hex digit or ':' (for ::)
+  ahead <- lookAhead (hexDigit <|> char ':')
+  case ahead of
+    ':' -> do
+      void (string "::")
+      right <- ipv6RightGroups
+      return ([], right)
+    _   -> do
+      left <- ipv6LeftGroups
+      mDbl <- optionMaybe (try (string "::"))
+      case mDbl of
+        Nothing -> return (left, [])
+        Just _  -> do
+          right <- ipv6RightGroups
+          return (left, right)
+
+-- Parse a run of hex16:hex16:... stopping before :: or end
+ipv6LeftGroups :: Parser [Int]
+ipv6LeftGroups = do
+  first <- hex16
+  rest  <- many (try (char ':' >> notFollowedBy (char ':') >> hex16))
+  return (first : rest)
+
+-- Parse groups to the right of ::, including optional embedded IPv4
+ipv6RightGroups :: Parser [Int]
+ipv6RightGroups = option [] $
+  try ipv4EmbeddedGroups <|> ipv6LeftGroups
+
+-- IPv4-mapped groups: e.g. ffff:192.168.1.1 -> [0xffff, 0xc0a8, 0x0101]
+ipv4EmbeddedGroups :: Parser [Int]
+ipv4EmbeddedGroups = do
+  prefix <- many (try (hex16 <* char ':' <* lookAhead digit))
+  a <- octet_; void (char '.')
+  b <- octet_; void (char '.')
+  c <- octet_; void (char '.')
+  d <- octet_
+  let hi = (a `shiftL` 8) .|. b
+      lo = (c `shiftL` 8) .|. d
+  return (prefix ++ [hi, lo])
+  where
+    octet_ = do
+      n <- fromIntegral <$> natural
+      if n > 255 then fail "IPv4 octet out of range" else return n
+
+hex16 :: Parser Int
+hex16 = do
+  digits <- many1 hexDigit
+  case (reads ("0x" ++ digits)) :: [(Int,String)] of
+    [(v,"")] -> if v > 0xffff then fail "hex16 out of range" else return v
+    _        -> fail "invalid hex group"
+
+cidrLit :: Parser CIDR
+cidrLit = do
+  l <- ipOrCidrLit
+  case l of
+    LCIDR ip p -> return (ip, p)
+    _          -> fail "expected CIDR notation (address/prefix)"

src/FWL/Pretty.hs

@@ -0,0 +1,187 @@
+-- | Pretty printer: round-trips the AST back to FWL source.
+module FWL.Pretty (prettyProgram) where
+
+import Data.List (intercalate)
+import FWL.AST
+
+prettyProgram :: Program -> String
+prettyProgram (Program cfg ds) =
+  prettyConfig cfg ++ "\n" ++ unlines (map prettyDecl ds)
+
+prettyConfig :: Config -> String
+prettyConfig (Config t)
+  | t == "fwl" = ""
+  | otherwise  = "config { table = \"" ++ t ++ "\"; }\n"
+
+prettyDecl :: Decl -> String
+prettyDecl (DInterface n k ps) =
+  "interface " ++ n ++ " : " ++ prettyKind k ++ " {\n" ++
+  concatMap (\p -> "  " ++ prettyIfaceProp p ++ ";\n") ps ++
+  "};"
+prettyDecl (DZone n ns) =
+  "zone " ++ n ++ " = { " ++ intercalate ", " ns ++ " };"
+prettyDecl (DImport n t s) =
+  "import " ++ n ++ " : " ++ prettyType t ++ " from \"" ++ s ++ "\";"
+prettyDecl (DLet n t e) =
+  "let " ++ n ++ " : " ++ prettyType t ++ " = " ++ prettyExpr e ++ ";"
+prettyDecl (DPattern n t p) =
+  "pattern " ++ n ++ " : " ++ prettyType t ++ " = " ++ prettyPat p ++ ";"
+prettyDecl (DFlow n f) =
+  "flow " ++ n ++ " : FlowPattern = " ++ prettyFlow f ++ ";"
+prettyDecl (DRule n t e) =
+  "rule " ++ n ++ " : " ++ prettyType t ++ " =\n  " ++ prettyExpr e ++ ";"
+prettyDecl (DPolicy n t pm ab) =
+  "policy " ++ n ++ " : " ++ prettyType t ++ "\n" ++
+  "  on { hook = " ++ prettyHook (pmHook pm) ++
+       ", table = " ++ prettyTable (pmTable pm) ++
+       ", priority = " ++ prettyPriority (pmPriority pm) ++ " }\n" ++
+  "  = " ++ prettyArmBlock ab ++ ";"
+
+prettyKind :: IfaceKind -> String
+prettyKind IWan        = "WAN"
+prettyKind ILan        = "LAN"
+prettyKind IWireGuard  = "WireGuard"
+prettyKind (IUser n)   = n
+
+prettyIfaceProp :: IfaceProp -> String
+prettyIfaceProp IPDynamic    = "dynamic"
+prettyIfaceProp (IPCidr4 cs) = "cidr4 = { " ++ intercalate ", " (map prettyCidr cs) ++ " }"
+prettyIfaceProp (IPCidr6 cs) = "cidr6 = { " ++ intercalate ", " (map prettyCidr cs) ++ " }"
+
+prettyCidr :: CIDR -> String
+prettyCidr (LIPv4 (a,b,c,d), p) =
+  show a ++ "." ++ show b ++ "." ++ show c ++ "." ++ show d ++ "/" ++ show p
+prettyCidr (ip, p) = prettyLit ip ++ "/" ++ show p
+
+prettyHook :: Hook -> String
+prettyHook HInput       = "Input"
+prettyHook HForward     = "Forward"
+prettyHook HOutput      = "Output"
+prettyHook HPrerouting  = "Prerouting"
+prettyHook HPostrouting = "Postrouting"
+
+prettyTable :: TableName -> String
+prettyTable TFilter = "Filter"
+prettyTable TNAT    = "NAT"
+
+prettyPriority :: Priority -> String
+prettyPriority p = show (priorityValue p)
+
+prettyType :: Type -> String
+prettyType (TName n [])   = n
+prettyType (TName n ts)   = n ++ "<" ++ intercalate ", " (map prettyType ts) ++ ">"
+prettyType (TTuple ts)    = "(" ++ intercalate ", " (map prettyType ts) ++ ")"
+prettyType (TFun a b)     = prettyType a ++ " -> " ++ prettyType b
+prettyType (TEffect es t) = "<" ++ intercalate ", " es ++ "> " ++ prettyType t
+
+prettyPat :: Pat -> String
+prettyPat PWild            = "_"
+prettyPat (PVar n)         = n
+prettyPat (PNamed n)       = n
+prettyPat (PCtor n ps)     = n ++ "(" ++ intercalate ", " (map prettyPat ps) ++ ")"
+prettyPat (PRecord n fs)   = n ++ " { " ++ intercalate ", " (map prettyFP fs) ++ " }"
+prettyPat (PTuple ps)      = "(" ++ intercalate ", " (map prettyPat ps) ++ ")"
+prettyPat (PFrame mp inner)=
+  "Frame(" ++ maybe "" (\pp -> prettyPath pp ++ ", ") mp ++ prettyPat inner ++ ")"
+prettyPat (PBytes bs)      = "[" ++ unwords (map prettyBE bs) ++ "]"
+
+prettyFP :: FieldPat -> String
+prettyFP (FPEq n l)  = n ++ " = " ++ prettyLit l
+prettyFP (FPBind n)  = n
+prettyFP (FPAs n v)  = n ++ " as " ++ v
+
+prettyPath :: PathPat -> String
+prettyPath (PathPat ms md) =
+  maybe "_" prettyEP ms ++ maybe "" (\d -> " -> " ++ prettyEP d) md
+
+prettyEP :: EndpointPat -> String
+prettyEP EPWild         = "_"
+prettyEP (EPName n)     = n
+prettyEP (EPMember n z) = n ++ " in " ++ z
+
+prettyBE :: ByteElem -> String
+prettyBE (BEHex w) = "0x" ++ pad (show w)  -- simplified
+  where pad s = if length s < 2 then '0':s else s
+prettyBE BEWild     = "_"
+prettyBE BEWildStar = "_*"
+
+prettyFlow :: FlowExpr -> String
+prettyFlow (FAtom n)      = n
+prettyFlow (FSeq a b mw)  =
+  prettyFlow a ++ " . " ++ prettyFlow b ++
+  maybe "" (\(n,u) -> " within " ++ show n ++ prettyUnit u) mw
+
+prettyUnit :: TimeUnit -> String
+prettyUnit Seconds = "s"
+prettyUnit Millis  = "ms"
+prettyUnit Minutes = "m"
+prettyUnit Hours   = "h"
+
+prettyExpr :: Expr -> String
+prettyExpr (EVar n)         = n
+prettyExpr (EQual ns)       = intercalate "." ns
+prettyExpr (ELit l)         = prettyLit l
+prettyExpr (ELam n e)       = "\\" ++ n ++ " -> " ++ prettyExpr e
+prettyExpr (EApp f x)       = prettyExpr f ++ " " ++ prettyAtom x
+prettyExpr (ECase e ab)     =
+  "case " ++ prettyExpr e ++ " of " ++ prettyArmBlock ab
+prettyExpr (EIf c t f)      =
+  "if " ++ prettyExpr c ++ " then " ++ prettyExpr t ++ " else " ++ prettyExpr f
+prettyExpr (EDo ss)         =
+  "do { " ++ intercalate "; " (map prettyStmt ss) ++ " }"
+prettyExpr (ELet n e1 e2)   =
+  "let " ++ n ++ " = " ++ prettyExpr e1 ++ " in " ++ prettyExpr e2
+prettyExpr (ETuple es)      = "(" ++ intercalate ", " (map prettyExpr es) ++ ")"
+prettyExpr (ESet es)        = "{ " ++ intercalate ", " (map prettyExpr es) ++ " }"
+prettyExpr (EMap ms)        =
+  "{ " ++ intercalate ", " (map (\(k,v) -> prettyExpr k ++ " -> " ++ prettyExpr v) ms) ++ " }"
+prettyExpr (EPerform ns as_) =
+  "perform " ++ intercalate "." ns ++ "(" ++ intercalate ", " (map prettyExpr as_) ++ ")"
+prettyExpr (EInfix op l r)  =
+  prettyAtom l ++ " " ++ prettyOp op ++ " " ++ prettyAtom r
+prettyExpr (ENot e)         = "!" ++ prettyAtom e
+
+prettyAtom :: Expr -> String
+prettyAtom e@(EInfix _ _ _) = "(" ++ prettyExpr e ++ ")"
+prettyAtom e@(ELam _ _)     = "(" ++ prettyExpr e ++ ")"
+prettyAtom e                 = prettyExpr e
+
+prettyOp :: InfixOp -> String
+prettyOp OpAnd    = "&&"
+prettyOp OpOr     = "||"
+prettyOp OpEq     = "=="
+prettyOp OpNeq    = "!="
+prettyOp OpLt     = "<"
+prettyOp OpLte    = "<="
+prettyOp OpGt     = ">"
+prettyOp OpGte    = ">="
+prettyOp OpIn     = "in"
+prettyOp OpConcat = "++"
+prettyOp OpThen   = ">>"
+prettyOp OpBind   = ">>="
+
+prettyStmt :: DoStmt -> String
+prettyStmt (DSBind n e) = n ++ " <- " ++ prettyExpr e
+prettyStmt (DSExpr e)   = prettyExpr e
+
+prettyArmBlock :: ArmBlock -> String
+prettyArmBlock arms =
+  "{\n" ++
+  concatMap (\(Arm p mg e) ->
+    "    | " ++ prettyPat p ++
+    maybe "" (\g -> " if " ++ prettyExpr g) mg ++
+    " -> " ++ prettyExpr e ++ ";\n") arms ++
+  "  }"
+
+prettyLit :: Literal -> String
+prettyLit (LInt n)           = show n
+prettyLit (LString s)        = "\"" ++ s ++ "\""
+prettyLit (LBool True)       = "true"
+prettyLit (LBool False)      = "false"
+prettyLit (LIPv4 (a,b,c,d))  =
+  show a ++ "." ++ show b ++ "." ++ show c ++ "." ++ show d
+prettyLit (LIPv6 _)          = "<ipv6>"
+prettyLit (LCIDR ip p)       = prettyLit ip ++ "/" ++ show p
+prettyLit (LPort p)          = ":" ++ show p
+prettyLit (LDuration n u)    = show n ++ prettyUnit u
+prettyLit (LHex b)           = "0x" ++ show b

test/CheckTests.hs

@@ -0,0 +1,224 @@
+module CheckTests (tests) where
+
+import Test.Tasty
+import Test.Tasty.HUnit
+
+import FWL.Check
+import FWL.Util
+
+tests :: TestTree
+tests = testGroup "Check"
+  [ undefinedNameTests
+  , duplicateTests
+  , policyTerminationTests
+  , patternCycleTests
+  , cleanProgramTests
+  ]
+
+-- ─── Helper ──────────────────────────────────────────────────────────────────
+
+checkSrc :: String -> IO [CheckError]
+checkSrc src = do
+  p <- parseOk src
+  return (checkProgram p)
+
+assertNoErrors :: String -> IO ()
+assertNoErrors src = do
+  errs <- checkSrc src
+  case errs of
+    [] -> return ()
+    _  -> assertFailure ("Unexpected errors: " ++ show errs)
+
+assertHasError :: (CheckError -> Bool) -> String -> IO ()
+assertHasError p src = do
+  errs <- checkSrc src
+  if any p errs
+    then return ()
+    else assertFailure ("Expected error not found. Got: " ++ show errs)
+
+isUndefined :: String -> CheckError -> Bool
+isUndefined n (UndefinedName _ m) = m == n
+isUndefined _ _                   = False
+
+isDuplicate :: String -> CheckError -> Bool
+isDuplicate n (DuplicateDecl _ m) = m == n
+isDuplicate _ _                   = False
+
+isNoContinue :: String -> CheckError -> Bool
+isNoContinue n (PolicyNoContinue m) = m == n
+isNoContinue _ _                    = False
+
+isCycle :: CheckError -> Bool
+isCycle (PatternCycle _) = True
+isCycle _                = False
+
+-- ─── Undefined name tests ────────────────────────────────────────────────────
+
+undefinedNameTests :: TestTree
+undefinedNameTests = testGroup "undefined names"
+  [ testCase "zone references unknown interface" $
+      assertHasError (isUndefined "ghost")
+        "zone bad_zone = { lan, ghost };"
+
+  , testCase "zone references known interface — no error" $
+      assertNoErrors
+        "interface lan : LAN {}; \
+        \zone good = { lan };"
+
+  , testCase "pattern references undefined named pattern" $
+      assertHasError (isUndefined "Undefined")
+        "pattern Bad : Frame = Frame(_, IPv4(ip, Undefined));"
+
+  , testCase "pattern references known named pattern — no error" $
+      assertNoErrors
+        "pattern WGInit : (UDPHeader,Bytes) = (udp { length = 156 }, [0x01 _*]); \
+        \pattern Compound : Frame = Frame(_, IPv4(ip, WGInit));"
+
+  , testCase "flow references undefined pattern" $
+      assertHasError (isUndefined "Ghost")
+        "flow Bad : FlowPattern = Ghost;"
+
+  , testCase "flow references known pattern — no error" $
+      assertNoErrors
+        "pattern P : T = udp { length = 1 }; \
+        \flow F : FlowPattern = P;"
+
+  , testCase "policy guard references undeclared zone" $
+      -- 'unknown_zone' not declared; check should flag it
+      assertHasError (isUndefined "unknown_zone")
+        "policy fwd : Frame \
+        \  on { hook = Forward, table = Filter, priority = Filter } \
+        \  = { | Frame(iif in unknown_zone -> wan, _) -> Allow; \
+        \      | _ -> Drop; \
+        \  };"
+
+  , testCase "policy references known zone — no error" $
+      assertNoErrors
+        "interface lan : LAN {}; \
+        \zone trusted = { lan }; \
+        \policy fwd : Frame \
+        \  on { hook = Forward, table = Filter, priority = Filter } \
+        \  = { | Frame(iif in trusted -> wan, _) -> Allow; \
+        \      | _ -> Drop; \
+        \  };"
+  ]
+
+-- ─── Duplicate declaration tests ─────────────────────────────────────────────
+
+duplicateTests :: TestTree
+duplicateTests = testGroup "duplicates"
+  [ testCase "duplicate interface" $
+      assertHasError (isDuplicate "lan")
+        "interface lan : LAN {}; \
+        \interface lan : WAN {};"
+
+  , testCase "duplicate zone" $
+      assertHasError (isDuplicate "z")
+        "zone z = { a }; \
+        \zone z = { b };"
+
+  , testCase "duplicate pattern" $
+      assertHasError (isDuplicate "P")
+        "pattern P : T = udp { length = 1 }; \
+        \pattern P : T = udp { length = 2 };"
+
+  , testCase "duplicate policy" $
+      assertHasError (isDuplicate "input")
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; }; \
+        \policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; };"
+
+  , testCase "distinct names — no error" $
+      assertNoErrors
+        "interface lan : LAN {}; \
+        \interface wan : WAN { dynamic; }; \
+        \zone z = { lan };"
+  ]
+
+-- ─── Policy termination tests ────────────────────────────────────────────────
+
+policyTerminationTests :: TestTree
+policyTerminationTests = testGroup "policy termination"
+  [ testCase "last arm is Continue — error" $
+      assertHasError (isNoContinue "bad_policy")
+        "policy bad_policy : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Continue; };"
+
+  , testCase "last arm is Drop — ok" $
+      assertNoErrors
+        "policy good : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ if ct.state in { Established } -> Allow; \
+        \      | _ -> Drop; \
+        \  };"
+
+  , testCase "last arm is Allow — ok" $
+      assertNoErrors
+        "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+
+  , testCase "Continue in non-last arm is fine" $
+      assertNoErrors
+        "rule r : Frame -> Action = \
+        \  \\f -> case f of { \
+        \    | Frame(_, IPv4(ip, _)) -> Continue; \
+        \    | _ -> Drop; \
+        \  };"
+
+  , testCase "empty policy body — error" $
+      assertHasError (isNoContinue "empty")
+        "policy empty : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = {};"
+  ]
+
+-- ─── Pattern cycle tests ─────────────────────────────────────────────────────
+
+patternCycleTests :: TestTree
+patternCycleTests = testGroup "pattern cycles"
+  [ testCase "direct self-reference — cycle error" $
+      assertHasError isCycle
+        "pattern Loop : T = Frame(_, Loop);"
+
+  , testCase "mutual cycle — cycle error" $
+      assertHasError isCycle
+        "pattern A : T = Frame(_, B); \
+        \pattern B : T = Frame(_, A);"
+
+  , testCase "linear chain — no cycle" $
+      assertNoErrors
+        "pattern Base : T = udp { length = 1 }; \
+        \pattern Mid  : T = Frame(_, Base); \
+        \pattern Top  : T = Frame(_, Mid);"
+  ]
+
+-- ─── Clean full programs ──────────────────────────────────────────────────────
+
+cleanProgramTests :: TestTree
+cleanProgramTests = testGroup "clean programs"
+  [ testCase "minimal router skeleton" $
+      assertNoErrors
+        "interface wan : WAN { dynamic; }; \
+        \interface lan : LAN { cidr4 = { 10.17.1.0/24 }; }; \
+        \interface wg0 : WireGuard {}; \
+        \zone lan_zone = { lan, wg0 }; \
+        \policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ if ct.state in { Established, Related } -> Allow; \
+        \      | _ -> Drop; \
+        \  }; \
+        \policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+
+  , testCase "pattern and flow declarations" $
+      assertNoErrors
+        "pattern WGInit : (UDPHeader,Bytes) = (udp { length = 156 }, [0x01 _*]); \
+        \pattern WGResp : (UDPHeader,Bytes) = (udp { length = 100 }, [0x02 _*]); \
+        \flow WGHandshake : FlowPattern = WGInit . WGResp within 5s;"
+  ]

test/CompileTests.hs

@@ -0,0 +1,384 @@
+{-# LANGUAGE OverloadedStrings #-}
+module CompileTests (tests) where
+
+import Test.Tasty
+import Test.Tasty.HUnit
+import qualified Data.Aeson as A
+import qualified Data.Aeson.Key as AK
+import qualified Data.Aeson.KeyMap as AKM
+import qualified Data.Vector as V
+import qualified Data.ByteString.Lazy.Char8 as BL8
+
+import FWL.AST
+import FWL.Compile
+import FWL.Util
+
+tests :: TestTree
+tests = testGroup "Compile"
+  [ jsonStructureTests
+  , chainTests
+  , ruleExprTests
+  , verdictTests
+  , layerStrippingTests
+  , continueTests
+  , configTests
+  ]
+
+-- ─── Helpers ─────────────────────────────────────────────────────────────────
+
+compileToValue :: String -> IO A.Value
+compileToValue src = do
+  p <- parseOk src
+  case A.decode (compileToJson p) of
+    Nothing -> assertFailure "Compiled output is not valid JSON" >> undefined
+    Just v  -> return v
+
+-- Navigate a Value by a list of string keys / numeric indices.
+at :: [String] -> A.Value -> Maybe A.Value
+at []     v                   = Just v
+at (k:ks) (A.Object o)        =
+  case AKM.lookup (AK.fromString k) o of
+    Nothing -> Nothing
+    Just v  -> at ks v
+at (k:ks) (A.Array arr)       =
+  case reads k of
+    [(i,"")] | i < V.length arr -> at ks (arr V.! i)
+    _                           -> Nothing
+at _ _ = Nothing
+
+nftArr :: A.Value -> IO [A.Value]
+nftArr v =
+  case at ["nftables"] v of
+    Just (A.Array arr) -> return (V.toList arr)
+    _                  -> assertFailure "Missing top-level 'nftables' array" >> undefined
+
+withKey :: String -> [A.Value] -> [A.Value]
+withKey k = filter (\v -> case at [k] v of Just _ -> True; _ -> False)
+
+-- ─── JSON structure tests ────────────────────────────────────────────────────
+
+jsonStructureTests :: TestTree
+jsonStructureTests = testGroup "JSON structure"
+  [ testCase "output is valid JSON" $ do
+      _ <- compileToValue
+        "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      return ()
+
+  , testCase "top-level nftables array present" $ do
+      v <- compileToValue "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      _ <- nftArr v
+      return ()
+
+  , testCase "metainfo is first element" $ do
+      v <- compileToValue "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      case arr of
+        (first:_) -> case at ["metainfo"] first of
+          Just _  -> return ()
+          Nothing -> assertFailure "First element is not metainfo"
+        [] -> assertFailure "Empty nftables array"
+
+  , testCase "table object present" $ do
+      v <- compileToValue "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      assertBool "Expected at least one table object"
+        (not (null (withKey "table" arr)))
+
+  , testCase "default table name is fwl" $ do
+      v <- compileToValue "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      case withKey "table" arr of
+        (t:_) -> at ["table","name"] t @?= Just (A.String "fwl")
+        []    -> assertFailure "No table object"
+
+  , testCase "custom table name respected" $ do
+      v <- compileToValue
+        "config { table = \"custom\"; } \
+        \policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      case withKey "table" arr of
+        (t:_) -> at ["table","name"] t @?= Just (A.String "custom")
+        []    -> assertFailure "No table object"
+  ]
+
+-- ─── Chain declaration tests ─────────────────────────────────────────────────
+
+chainTests :: TestTree
+chainTests = testGroup "chain declarations"
+  [ testCase "filter input chain has correct hook" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; };"
+      arr <- nftArr v
+      case withKey "chain" arr of
+        (c:_) -> at ["chain","hook"] c @?= Just (A.String "input")
+        []    -> assertFailure "No chain"
+
+  , testCase "filter chain type is filter" $ do
+      v <- compileToValue
+        "policy fwd : Frame \
+        \  on { hook = Forward, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; };"
+      arr <- nftArr v
+      case withKey "chain" arr of
+        (c:_) -> at ["chain","type"] c @?= Just (A.String "filter")
+        []    -> assertFailure "No chain"
+
+  , testCase "NAT chain type is nat" $ do
+      v <- compileToValue
+        "policy nat_post : Frame \
+        \  on { hook = Postrouting, table = NAT, priority = SrcNat } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      case withKey "chain" arr of
+        (c:_) -> at ["chain","type"] c @?= Just (A.String "nat")
+        []    -> assertFailure "No chain"
+
+  , testCase "input chain default policy is drop" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; };"
+      arr <- nftArr v
+      case withKey "chain" arr of
+        (c:_) -> at ["chain","policy"] c @?= Just (A.String "drop")
+        []    -> assertFailure "No chain"
+
+  , testCase "output chain default policy is accept" $ do
+      v <- compileToValue
+        "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      case withKey "chain" arr of
+        (c:_) -> at ["chain","policy"] c @?= Just (A.String "accept")
+        []    -> assertFailure "No chain"
+
+  , testCase "chain name matches policy name" $ do
+      v <- compileToValue
+        "policy my_input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; };"
+      arr <- nftArr v
+      case withKey "chain" arr of
+        (c:_) -> at ["chain","name"] c @?= Just (A.String "my_input")
+        []    -> assertFailure "No chain"
+
+  , testCase "two policies produce two chains" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; }; \
+        \policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      length (withKey "chain" arr) @?= 2
+  ]
+
+-- ─── Rule expression tests ───────────────────────────────────────────────────
+
+ruleExprs :: [A.Value] -> [A.Value]
+ruleExprs arr =
+  [ e | r  <- withKey "rule" arr
+      , Just (A.Array es) <- [at ["rule","expr"] r]
+      , e  <- V.toList es ]
+
+ruleExprTests :: TestTree
+ruleExprTests = testGroup "rule expressions"
+  [ testCase "two arms produce two rules" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ if ct.state in { Established, Related } -> Allow; \
+        \      | _ -> Drop; \
+        \  };"
+      arr <- nftArr v
+      length (withKey "rule" arr) @?= 2
+
+  , testCase "arm without guard produces one rule" $ do
+      v <- compileToValue
+        "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      length (withKey "rule" arr) @?= 1
+
+  , testCase "rule expr array is present" $ do
+      v <- compileToValue
+        "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      case withKey "rule" arr of
+        (r:_) -> case at ["rule","expr"] r of
+          Just (A.Array _) -> return ()
+          _                -> assertFailure "Missing or non-array 'expr'"
+        [] -> assertFailure "No rule"
+
+  , testCase "IPv4 ctor emits nfproto match" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | Frame(_, IPv4(ip, _)) -> Allow; \
+        \      | _ -> Drop; \
+        \  };"
+      arr <- nftArr v
+      let matches   = withKey "match" (ruleExprs arr)
+          hasNfp    = any (\m ->
+            at ["match","left","meta","key"] m == Just (A.String "nfproto"))
+            matches
+      assertBool "Expected nfproto match for IPv4 ctor" hasNfp
+
+  , testCase "record field pat emits payload match" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | Frame(_, TCP(tcp { dport = :22 }, _)) -> Allow; \
+        \      | _ -> Drop; \
+        \  };"
+      arr <- nftArr v
+      let matches  = withKey "match" (ruleExprs arr)
+          hasPort  = any (\m ->
+            at ["match","right"] m == Just (A.String "22"))
+            matches
+      assertBool "Expected port 22 payload match" hasPort
+  ]
+
+-- ─── Verdict tests ───────────────────────────────────────────────────────────
+
+allExprs :: [A.Value] -> [A.Value]
+allExprs arr =
+  concatMap (\r -> case at ["rule","expr"] r of
+    Just (A.Array es) -> V.toList es; _ -> [])
+  (withKey "rule" arr)
+
+verdictTests :: TestTree
+verdictTests = testGroup "verdicts"
+  [ testCase "Allow compiles to accept" $ do
+      v <- compileToValue
+        "policy output : Frame \
+        \  on { hook = Output, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+      arr <- nftArr v
+      assertBool "Expected accept verdict"
+        (not (null (withKey "accept" (allExprs arr))))
+
+  , testCase "Drop compiles to drop" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; };"
+      arr <- nftArr v
+      assertBool "Expected drop verdict"
+        (not (null (withKey "drop" (allExprs arr))))
+
+  , testCase "Masquerade compiles to masquerade" $ do
+      v <- compileToValue
+        "policy nat_post : Frame \
+        \  on { hook = Postrouting, table = NAT, priority = SrcNat } \
+        \  = { | _ -> Masquerade; };"
+      arr <- nftArr v
+      assertBool "Expected masquerade verdict"
+        (not (null (withKey "masquerade" (allExprs arr))))
+
+  , testCase "rule call compiles to jump" $ do
+      v <- compileToValue
+        "rule blockAll : Frame -> Action = \\f -> case f of { | _ -> Drop; }; \
+        \policy fwd : Frame \
+        \  on { hook = Forward, table = Filter, priority = Filter } \
+        \  = { | frame -> blockAll(frame); };"
+      arr <- nftArr v
+      assertBool "Expected jump verdict for rule call"
+        (not (null (withKey "jump" (allExprs arr))))
+  ]
+
+-- ─── Layer stripping tests ───────────────────────────────────────────────────
+
+layerStrippingTests :: TestTree
+layerStrippingTests = testGroup "layer stripping"
+  [ testCase "Frame with and without Ether both emit nfproto match" $ do
+      let withEther =
+            "policy p1 : Frame \
+            \  on { hook = Input, table = Filter, priority = Filter } \
+            \  = { | Frame(_, Ether(_, IPv4(ip, _))) -> Allow; \
+            \      | _ -> Drop; \
+            \  };"
+          withoutEther =
+            "policy p1 : Frame \
+            \  on { hook = Input, table = Filter, priority = Filter } \
+            \  = { | Frame(_, IPv4(ip, _)) -> Allow; \
+            \      | _ -> Drop; \
+            \  };"
+      v1 <- compileToValue withEther
+      v2 <- compileToValue withoutEther
+      arr1 <- nftArr v1
+      arr2 <- nftArr v2
+      let nfp arr = filter
+            (\m -> at ["match","left","meta","key"] m == Just (A.String "nfproto"))
+            (withKey "match" (ruleExprs arr))
+      assertBool "Both should produce nfproto matches"
+        (not (null (nfp arr1)) && not (null (nfp arr2)))
+  ]
+
+-- ─── Continue tests ───────────────────────────────────────────────────────────
+
+continueTests :: TestTree
+continueTests = testGroup "Continue"
+  [ testCase "two terminal arms produce two rules" $ do
+      v <- compileToValue
+        "policy fwd : Frame \
+        \  on { hook = Forward, table = Filter, priority = Filter } \
+        \  = { | _ if ct.state in { Established } -> Allow; \
+        \      | _ -> Drop; \
+        \  };"
+      arr <- nftArr v
+      length (withKey "rule" arr) @?= 2
+
+  , testCase "non-Continue arms still produce rules" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ if ct.state in { Established } -> Allow; \
+        \      | _ -> Drop; \
+        \  };"
+      arr <- nftArr v
+      assertBool "Should have rules for non-Continue arms"
+        (not (null (withKey "rule" arr)))
+  ]
+
+-- ─── Config tests ─────────────────────────────────────────────────────────────
+
+configTests :: TestTree
+configTests = testGroup "config"
+  [ testCase "all rule objects reference correct table" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; };"
+      arr <- nftArr v
+      mapM_ (\r -> at ["rule","table"] r @?= Just (A.String "fwl"))
+        (withKey "rule" arr)
+
+  , testCase "chain objects reference correct table" $ do
+      v <- compileToValue
+        "policy input : Frame \
+        \  on { hook = Input, table = Filter, priority = Filter } \
+        \  = { | _ -> Drop; };"
+      arr <- nftArr v
+      mapM_ (\c -> at ["chain","table"] c @?= Just (A.String "fwl"))
+        (withKey "chain" arr)
+  ]

test/FWL/Util.hs

@@ -0,0 +1,44 @@
+-- | Shared test utilities.
+module FWL.Util where
+
+import Test.Tasty.HUnit
+import Text.Parsec.String (Parser)
+import Text.Parsec (parse)
+
+import FWL.Parser (parseProgram)
+import FWL.AST
+
+-- | Assert a parser succeeds and return the result.
+shouldParse :: (Show a) => Parser a -> String -> IO a
+shouldParse p input =
+  case parse p "<test>" input of
+    Left err -> assertFailure ("Unexpected parse error:\n" ++ show err)
+                >> undefined
+    Right v  -> return v
+
+-- | Assert a parser fails.
+shouldFailParse :: (Show a) => Parser a -> String -> IO ()
+shouldFailParse p input =
+  case parse p "<test>" input of
+    Left _  -> return ()
+    Right v -> assertFailure ("Expected parse failure but got: " ++ show v)
+
+-- | Parse a full program, asserting success.
+parseOk :: String -> IO Program
+parseOk src =
+  case parseProgram "<test>" src of
+    Left err -> assertFailure ("Parse error:\n" ++ show err) >> undefined
+    Right p  -> return p
+
+-- | Parse a full program, asserting failure.
+parseFail :: String -> IO ()
+parseFail src =
+  case parseProgram "<test>" src of
+    Left _  -> return ()
+    Right p -> assertFailure ("Expected parse failure, got:\n" ++ show p)
+
+-- | Extract the single declaration from a one-decl program.
+singleDecl :: Program -> IO Decl
+singleDecl (Program _ [d]) = return d
+singleDecl (Program _ ds)  =
+  assertFailure ("Expected 1 decl, got " ++ show (length ds)) >> undefined

test/ParserTests.hs

@@ -0,0 +1,516 @@
+module ParserTests (tests) where
+
+import Test.Tasty
+import Test.Tasty.HUnit
+
+import FWL.AST
+import FWL.Util
+
+tests :: TestTree
+tests = testGroup "Parser"
+  [ interfaceTests
+  , zoneTests
+  , importTests
+  , letTests
+  , patternTests
+  , flowTests
+  , typeTests
+  , exprTests
+  , policyTests
+  , ruleTests
+  , configTests
+  , errorTests
+  ]
+
+-- ─── Interface ───────────────────────────────────────────────────────────────
+
+interfaceTests :: TestTree
+interfaceTests = testGroup "interface"
+  [ testCase "WAN dynamic" $ do
+      p <- parseOk "interface wan : WAN { dynamic; };"
+      d <- singleDecl p
+      case d of
+        DInterface "wan" IWan [IPDynamic] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "LAN with cidr4" $ do
+      p <- parseOk "interface lan : LAN { cidr4 = { 10.0.0.0/8 }; };"
+      d <- singleDecl p
+      case d of
+        DInterface "lan" ILan [IPCidr4 [(LIPv4 (10,0,0,0), 8)]] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "LAN with cidr4 and cidr6" $ do
+      p <- parseOk
+            "interface lan : LAN { \
+            \  cidr4 = { 10.17.1.0/24 }; \
+            \  cidr6 = { 192.168.0.0/16 }; \
+            \};"
+      d <- singleDecl p
+      case d of
+        DInterface "lan" ILan [IPCidr4 _, IPCidr6 _] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "WireGuard interface" $ do
+      p <- parseOk "interface wg0 : WireGuard {};"
+      d <- singleDecl p
+      case d of
+        DInterface "wg0" IWireGuard [] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "user-defined kind" $ do
+      p <- parseOk "interface eth0 : Bridge {};"
+      d <- singleDecl p
+      case d of
+        DInterface "eth0" (IUser "Bridge") [] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "multiple CIDRs in set" $ do
+      p <- parseOk
+            "interface lan : LAN { \
+            \  cidr4 = { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 }; \
+            \};"
+      d <- singleDecl p
+      case d of
+        DInterface _ _ [IPCidr4 cidrs] -> length cidrs @?= 3
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Zone ────────────────────────────────────────────────────────────────────
+
+zoneTests :: TestTree
+zoneTests = testGroup "zone"
+  [ testCase "single member" $ do
+      p <- parseOk "zone trusted = { lan };"
+      d <- singleDecl p
+      case d of
+        DZone "trusted" ["lan"] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "multiple members" $ do
+      p <- parseOk "zone lan_zone = { lan, wg0, vlan10 };"
+      d <- singleDecl p
+      case d of
+        DZone "lan_zone" ["lan","wg0","vlan10"] -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Import ──────────────────────────────────────────────────────────────────
+
+importTests :: TestTree
+importTests = testGroup "import"
+  [ testCase "basic import" $ do
+      p <- parseOk "import rfc1918 : CIDRSet from \"builtin:rfc1918\";"
+      d <- singleDecl p
+      case d of
+        DImport "rfc1918" (TName "CIDRSet" []) "builtin:rfc1918" -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Let ─────────────────────────────────────────────────────────────────────
+
+letTests :: TestTree
+letTests = testGroup "let"
+  [ testCase "simple integer" $ do
+      p <- parseOk "let timeout : Int = 30;"
+      d <- singleDecl p
+      case d of
+        DLet "timeout" (TName "Int" []) (ELit (LInt 30)) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "map literal" $ do
+      p <- parseOk
+            "let forwards : Map<(Protocol,Port),(IP,Port)> = { \
+            \  (tcp, :8080) -> (10.0.0.1, :80) \
+            \};"
+      d <- singleDecl p
+      case d of
+        DLet "forwards" _ (EMap [_]) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "string literal" $ do
+      p <- parseOk "let name : String = \"hello\";"
+      d <- singleDecl p
+      case d of
+        DLet "name" _ (ELit (LString "hello")) -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Pattern ─────────────────────────────────────────────────────────────────
+
+patternTests :: TestTree
+patternTests = testGroup "pattern"
+  [ testCase "tuple with record field" $ do
+      p <- parseOk
+            "pattern WGInitiation : (UDPHeader, Bytes) = \
+            \  (udp { length = 156 }, [0x01 _*]);"
+      d <- singleDecl p
+      case d of
+        DPattern "WGInitiation" _ (PTuple [PRecord "udp" _, PBytes _]) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "byte pattern elements" $ do
+      p <- parseOk
+            "pattern WGResponse : (UDPHeader, Bytes) = \
+            \  (udp { length = 100 }, [0x02 _ _*]);"
+      d <- singleDecl p
+      case d of
+        DPattern "WGResponse" _ (PTuple [_, PBytes [BEHex 0x02, BEWild, BEWildStar]]) ->
+          return ()
+        _ -> assertFailure (show d)
+
+  , testCase "named pattern reference in ctor" $ do
+      p <- parseOk
+            "pattern Complex : Frame = \
+            \  Frame(_, IPv4(ip, WGInitiation));"
+      d <- singleDecl p
+      case d of
+        DPattern "Complex" _ (PFrame Nothing (PCtor "IPv4" [PVar "ip", PNamed "WGInitiation"])) ->
+          return ()
+        _ -> assertFailure (show d)
+
+  , testCase "record with field bind" $ do
+      p <- parseOk "pattern HasTCP : TCP = tcp { dport };"
+      d <- singleDecl p
+      case d of
+        DPattern "HasTCP" _ (PRecord "tcp" [FPBind "dport"]) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "record with field equality" $ do
+      p <- parseOk "pattern SSH : TCP = tcp { dport = :22 };"
+      d <- singleDecl p
+      case d of
+        DPattern "SSH" _ (PRecord "tcp" [FPEq "dport" (LPort 22)]) -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Flow ────────────────────────────────────────────────────────────────────
+
+flowTests :: TestTree
+flowTests = testGroup "flow"
+  [ testCase "two-step sequence with within" $ do
+      p <- parseOk
+            "flow WireGuardHandshake : FlowPattern = \
+            \  WGInitiation . WGResponse within 5s;"
+      d <- singleDecl p
+      case d of
+        DFlow "WireGuardHandshake" (FSeq (FAtom "WGInitiation") (FAtom "WGResponse") (Just (5, Seconds))) ->
+          return ()
+        _ -> assertFailure (show d)
+
+  , testCase "single atom flow" $ do
+      p <- parseOk "flow Simple : FlowPattern = Ping;"
+      d <- singleDecl p
+      case d of
+        DFlow "Simple" (FAtom "Ping") -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "duration in milliseconds" $ do
+      p <- parseOk "flow Fast : FlowPattern = A . B within 500ms;"
+      d <- singleDecl p
+      case d of
+        DFlow "Fast" (FSeq _ _ (Just (500, Millis))) -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Types ───────────────────────────────────────────────────────────────────
+
+typeTests :: TestTree
+typeTests = testGroup "types"
+  [ testCase "simple name" $ do
+      p <- parseOk "let x : Frame = Allow;"
+      d <- singleDecl p
+      case d of
+        DLet _ (TName "Frame" []) _ -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "generic type" $ do
+      p <- parseOk "let x : Map<Int, String> = Allow;"
+      d <- singleDecl p
+      case d of
+        DLet _ (TName "Map" [TName "Int" [], TName "String" []]) _ -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "function type" $ do
+      p <- parseOk "let x : Frame -> Action = Allow;"
+      d <- singleDecl p
+      case d of
+        DLet _ (TFun (TName "Frame" []) (TName "Action" [])) _ -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "effect type" $ do
+      p <- parseOk "let x : <Log, FlowMatch> Action = Allow;"
+      d <- singleDecl p
+      case d of
+        DLet _ (TEffect ["Log","FlowMatch"] (TName "Action" [])) _ -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "tuple type" $ do
+      p <- parseOk "let x : (Int, String) = Allow;"
+      d <- singleDecl p
+      case d of
+        DLet _ (TTuple [TName "Int" [], TName "String" []]) _ -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "function with effects" $ do
+      p <- parseOk "let x : Frame -> <Log> Action = Allow;"
+      d <- singleDecl p
+      case d of
+        DLet _ (TFun _ (TEffect ["Log"] _)) _ -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Expressions ─────────────────────────────────────────────────────────────
+
+exprTests :: TestTree
+exprTests = testGroup "expressions"
+  [ testCase "boolean and" $ do
+      p <- parseOk "let x : Bool = a && b;"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (EInfix OpAnd (EVar "a") (EVar "b")) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "set membership with 'in'" $ do
+      p <- parseOk "let x : Bool = ct.state in { Established, Related };"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (EInfix OpIn (EQual ["ct","state"]) (ESet _)) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "equality comparison" $ do
+      p <- parseOk "let x : Bool = tcp.dport == :22;"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (EInfix OpEq (EQual ["tcp","dport"]) (ELit (LPort 22))) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "if-then-else" $ do
+      p <- parseOk "let x : Action = if a then Allow else Drop;"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (EIf (EVar "a") (EVar "Allow") (EVar "Drop")) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "perform expression" $ do
+      p <- parseOk "let x : Action = perform Log.emit(Info, \"msg\");"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (EPerform ["Log","emit"] [ELit (LString "Info"), ELit (LString "msg")]) -> return ()
+        DLet _ _ (EPerform ["Log","emit"] _) -> return ()  -- arg parsing flexible
+        _ -> assertFailure (show d)
+
+  , testCase "do block" $ do
+      p <- parseOk "let x : Action = do { y <- foo; y };"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (EDo [DSBind "y" _, DSExpr (EVar "y")]) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "nested case" $ do
+      p <- parseOk
+            "let x : Action = case e of { \
+            \  | a -> Allow; \
+            \  | _ -> Drop; \
+            \};"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (ECase (EVar "e") [Arm (PVar "a") Nothing _, Arm PWild Nothing _]) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "lambda" $ do
+      p <- parseOk "let x : Frame -> Action = \\frame -> Allow;"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (ELam "frame" (EVar "Allow")) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "string concat" $ do
+      p <- parseOk "let x : String = \"hello\" ++ \" world\";"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (EInfix OpConcat _ _) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "negation" $ do
+      p <- parseOk "let x : Bool = !flag;"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (ENot (EVar "flag")) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "set literal" $ do
+      p <- parseOk "let x : Set<Int> = { 22, 80, 443 };"
+      d <- singleDecl p
+      case d of
+        DLet _ _ (ESet [ELit (LInt 22), ELit (LInt 80), ELit (LInt 443)]) -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Policy ──────────────────────────────────────────────────────────────────
+
+policyTests :: TestTree
+policyTests = testGroup "policy"
+  [ testCase "minimal policy" $ do
+      p <- parseOk
+            "policy output : Frame \
+            \  on { hook = Output, table = Filter, priority = Filter } \
+            \  = { | _ -> Allow; };"
+      d <- singleDecl p
+      case d of
+        DPolicy "output" _ (PolicyMeta HOutput TFilter (Priority 0)) [_] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "NAT prerouting" $ do
+      p <- parseOk
+            "policy nat_pre : Frame \
+            \  on { hook = Prerouting, table = NAT, priority = DstNat } \
+            \  = { | _ -> Allow; };"
+      d <- singleDecl p
+      case d of
+        DPolicy _ _ (PolicyMeta HPrerouting TNAT (Priority (-100))) _ -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "arm with guard" $ do
+      p <- parseOk
+            "policy input : Frame \
+            \  on { hook = Input, table = Filter, priority = Filter } \
+            \  = { \
+            \    | _ if ct.state in { Established, Related } -> Allow; \
+            \    | _ -> Drop; \
+            \  };"
+      d <- singleDecl p
+      case d of
+        DPolicy _ _ _ [Arm PWild (Just _) _, Arm PWild Nothing _] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "Frame pattern with path" $ do
+      p <- parseOk
+            "policy forward : Frame \
+            \  on { hook = Forward, table = Filter, priority = Filter } \
+            \  = { \
+            \    | Frame(iif in lan_zone -> wan, _) -> Allow; \
+            \    | _ -> Drop; \
+            \  };"
+      d <- singleDecl p
+      case d of
+        DPolicy _ _ _ (Arm (PFrame (Just _) _) Nothing _ : _) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "Frame pattern without Ether (layer stripping)" $ do
+      p <- parseOk
+            "policy input : Frame \
+            \  on { hook = Input, table = Filter, priority = Filter } \
+            \  = { \
+            \    | Frame(_, IPv4(ip, TCP(tcp, _))) if tcp.dport == :22 -> Allow; \
+            \    | _ -> Drop; \
+            \  };"
+      d <- singleDecl p
+      case d of
+        DPolicy _ _ _ (Arm (PFrame Nothing (PCtor "IPv4" _)) _ _ : _) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "policy arm calls rule" $ do
+      p <- parseOk
+            "policy forward : Frame \
+            \  on { hook = Forward, table = Filter, priority = Filter } \
+            \  = { \
+            \    | frame -> blockOutboundWG(frame); \
+            \  };"
+      d <- singleDecl p
+      case d of
+        DPolicy _ _ _ [Arm (PVar "frame") Nothing (EApp (EVar "blockOutboundWG") _)] ->
+          return ()
+        _ -> assertFailure (show d)
+
+  , testCase "Continue arm is parsed" $ do
+      p <- parseOk
+            "rule r : Frame -> Action = \
+            \  \\frame -> case frame of { \
+            \    | _ -> Continue; \
+            \  };"
+      d <- singleDecl p
+      case d of
+        DRule _ _ _ -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Rule ────────────────────────────────────────────────────────────────────
+
+ruleTests :: TestTree
+ruleTests = testGroup "rule"
+  [ testCase "simple rule" $ do
+      p <- parseOk
+            "rule blockAll : Frame -> Action = \
+            \  \\frame -> case frame of { | _ -> Drop; };"
+      d <- singleDecl p
+      case d of
+        DRule "blockAll" _ (ELam "frame" (ECase _ _)) -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "rule with effects in type" $ do
+      p <- parseOk
+            "rule logged : Frame -> <Log> Action = \
+            \  \\f -> case f of { | _ -> Allow; };"
+      d <- singleDecl p
+      case d of
+        DRule "logged" (TFun _ (TEffect ["Log"] _)) _ -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "nested case in rule" $ do
+      p <- parseOk
+            "rule check : Frame -> <FlowMatch> Action = \
+            \  \\frame -> \
+            \    case frame of { \
+            \      | Frame(_, IPv4(ip, UDP(udp, _))) -> \
+            \          case perform FlowMatch.check(ip, wg) of { \
+            \            | Matched -> Drop; \
+            \            | _ -> Continue; \
+            \          }; \
+            \      | _ -> Continue; \
+            \    };"
+      d <- singleDecl p
+      case d of
+        DRule "check" _ (ELam _ (ECase _ _)) -> return ()
+        _ -> assertFailure (show d)
+  ]
+
+-- ─── Config ──────────────────────────────────────────────────────────────────
+
+configTests :: TestTree
+configTests = testGroup "config"
+  [ testCase "default table name" $ do
+      p <- parseOk "interface wan : WAN {};"
+      configTable (progConfig p) @?= "fwl"
+
+  , testCase "custom table name" $ do
+      p <- parseOk "config { table = \"myrules\"; } interface wan : WAN {};"
+      configTable (progConfig p) @?= "myrules"
+  ]
+
+-- ─── Error cases ─────────────────────────────────────────────────────────────
+
+errorTests :: TestTree
+errorTests = testGroup "parse errors"
+  [ testCase "missing semicolon" $
+      parseFail "interface wan : WAN {}"
+
+  , testCase "unknown hook" $
+      parseFail
+        "policy p : Frame \
+        \  on { hook = Bogus, table = Filter, priority = Filter } \
+        \  = { | _ -> Allow; };"
+
+  , testCase "empty arm block with no arms is ok" $ do
+      p <- parseOk
+            "policy output : Frame \
+            \  on { hook = Output, table = Filter, priority = Filter } \
+            \  = {};"
+      d <- singleDecl p
+      case d of
+        DPolicy _ _ _ [] -> return ()
+        _ -> assertFailure (show d)
+
+  , testCase "CIDR without prefix fails" $
+      parseFail "interface lan : LAN { cidr4 = { 10.0.0.1 }; };"
+  ]

test/Spec.hs

@@ -0,0 +1,15 @@
+module Main where
+
+import Test.Tasty
+import Test.Tasty.HUnit
+
+import qualified ParserTests
+import qualified CheckTests
+import qualified CompileTests
+
+main :: IO ()
+main = defaultMain $ testGroup "FWL"
+  [ ParserTests.tests
+  , CheckTests.tests
+  , CompileTests.tests
+  ]