{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

{-# OPTIONS_GHC -Wall #-}

{-| An IP data type representing either an IPv4 address or
    an IPv6 address. The user can think of this
    as though it were a sum type. However, to minimize indirections,
    it is actually implemented as an 'IPv6' address, with 'IPv4'
    addresses being represented as an IPv4-mapped IPv6 addresses:

    > +---------+---------+--------------+
    > | 80 bits | 16 bits | 32 bits      |
    > +---------+---------+--------------+
    > | 00...00 | FFFF    | IPv4 address |
    > +---------+---------+--------------+

    All functions and instance methods that deal with textual conversion
    will encode an 'IP' using either dot-decimal notation (for IPv4) or
    RFC 5952 (for IPv6). They will decode an 'IP' from either format
    as well. The 'Show' instance presents an address in as valid haskell code
    that resembles the formatted address:

    >>> decode "192.168.3.100"
    Just (ipv4 192 168 3 100)
    >>> decode "A3F5:12:F26::1466:8B91"
    Just (ipv6 0xa3f5 0x0012 0x0f26 0x0000 0x0000 0x0000 0x1466 0x8b91)
-}

module Net.IP
  ( -- * Pattern Matching
    case_
  , isIPv4
  , isIPv6
    -- * Construction
  , ipv4
  , ipv6
  , fromIPv4
  , fromIPv6
    -- * Textual Conversion
    -- ** Text
  , encode
  , encodeShort
  , decode
  , decodeShort
  , boundedBuilderUtf8
    -- ** Bytes
  , decodeUtf8Bytes
  , parserUtf8Bytes
    -- ** Printing
  , print
    -- * Types
  , IP(..)
  ) where

import Control.DeepSeq (NFData)
import Data.Aeson (FromJSON(..),ToJSON(..))
import Data.Bits
import Data.Coerce (coerce)
import Data.Data (Data)
import Data.Hashable (Hashable)
import Data.Ix (Ix)
import Data.Text (Text)
import Data.WideWord (Word128(..))
import Data.Word (Word8,Word16)
import GHC.Generics (Generic)
import Net.IPv4 (IPv4(..))
import Net.IPv6 (IPv6(..))
import Prelude hiding (print)
import Text.ParserCombinators.ReadPrec ((+++))
import Text.Read (Read(..))
import Data.Text.Short (ShortText)

import qualified Arithmetic.Lte as Lte
import qualified Data.Aeson as Aeson
import qualified Data.Bytes as Bytes
import qualified Data.Bytes.Builder.Bounded as BB
import qualified Data.Text.IO as TIO
import qualified Data.Bytes.Parser as Parser
import qualified Net.IPv4 as IPv4
import qualified Net.IPv6 as IPv6

-- $setup
-- >>> :set -XOverloadedStrings
-- >>> import qualified Arithmetic.Nat as Nat

-- | Run a function over an 'IP' depending on its status
--   as an 'IPv4' or 'IPv6'.
--
--   >>> case_ IPv4.encode IPv6.encode (ipv4 192 168 2 47)
--   "192.168.2.47"
--
--   >>> addr = ipv6 0x2001 0x0db8 0x0000 0x0000 0x0000 0x0000 0x0000 0x0001
--   >>> case_ IPv4.encode IPv6.encode addr
--   "2001:db8::1"
case_ :: (IPv4 -> a) -> (IPv6 -> a) -> IP -> a
-- Note: rather than performing the masking operations on the 'Word128',
-- we unwrap the 'Word64's, as that's probably a bit more efficient, and
-- we might need the lower word anyway.
case_ :: forall a. (IPv4 -> a) -> (IPv6 -> a) -> IP -> a
case_ IPv4 -> a
f IPv6 -> a
g (IP addr :: IPv6
addr@(IPv6 (Word128 Word64
w1 Word64
w2))) = if Word64
w1 forall a. Eq a => a -> a -> Bool
== Word64
0 Bool -> Bool -> Bool
&& (Word64
0xFFFFFFFF00000000 forall a. Bits a => a -> a -> a
.&. Word64
w2 forall a. Eq a => a -> a -> Bool
== Word64
0x0000FFFF00000000)
  then IPv4 -> a
f (Word32 -> IPv4
IPv4 (forall a b. (Integral a, Num b) => a -> b
fromIntegral Word64
w2))
  else IPv6 -> a
g IPv6
addr

-- | Construct an 'IP' address from the four octets of
--   an IPv4 address.
ipv4 :: Word8 -> Word8 -> Word8 -> Word8 -> IP
ipv4 :: Word8 -> Word8 -> Word8 -> Word8 -> IP
ipv4 Word8
a Word8
b Word8
c Word8
d = IPv4 -> IP
fromIPv4 (Word8 -> Word8 -> Word8 -> Word8 -> IPv4
IPv4.fromOctets Word8
a Word8
b Word8
c Word8
d)

-- | Construct an 'IP' address from the eight 16-bit
--   chunks of an IPv6 address.
ipv6 :: Word16 -> Word16 -> Word16 -> Word16
     -> Word16 -> Word16 -> Word16 -> Word16
     -> IP
ipv6 :: Word16
-> Word16
-> Word16
-> Word16
-> Word16
-> Word16
-> Word16
-> Word16
-> IP
ipv6 Word16
a Word16
b Word16
c Word16
d Word16
e Word16
f Word16
g Word16
h = IPv6 -> IP
fromIPv6 (Word16
-> Word16
-> Word16
-> Word16
-> Word16
-> Word16
-> Word16
-> Word16
-> IPv6
IPv6.fromWord16s Word16
a Word16
b Word16
c Word16
d Word16
e Word16
f Word16
g Word16
h)

-- | Turn an 'IPv4' into an 'IP'.
fromIPv4 :: IPv4 -> IP
fromIPv4 :: IPv4 -> IP
fromIPv4 (IPv4 Word32
w) = IPv6 -> IP
IP (Word128 -> IPv6
IPv6 (Word64 -> Word64 -> Word128
Word128 Word64
0 (Word64
0x0000FFFF00000000 forall a. Bits a => a -> a -> a
.|. forall a b. (Integral a, Num b) => a -> b
fromIntegral Word32
w)))

-- | Turn an 'IPv6' into an 'IP'.
fromIPv6 :: IPv6 -> IP
fromIPv6 :: IPv6 -> IP
fromIPv6 = IPv6 -> IP
IP

-- | Encode an 'IP' as 'Text'.
--
--   >>> encode (ipv4 10 0 0 25)
--   "10.0.0.25"
--
--   >>> encode (ipv6 0x3124 0x0 0x0 0xDEAD 0xCAFE 0xFF 0xFE00 0x1)
--   "3124::dead:cafe:ff:fe00:1"
encode :: IP -> Text
encode :: IP -> Text
encode = forall a. (IPv4 -> a) -> (IPv6 -> a) -> IP -> a
case_ IPv4 -> Text
IPv4.encode IPv6 -> Text
IPv6.encode

-- | Encode an 'IP' as 'ShortText'.
--
--   >>> encodeShort (ipv4 10 0 1 26)
--   "10.0.1.26"
--
--   >>> encodeShort (ipv6 0x3124 0x0 0x0 0xDEAD 0xCAFE 0xFF 0xFE01 0x0000)
--   "3124::dead:cafe:ff:fe01:0"
encodeShort :: IP -> ShortText
encodeShort :: IP -> ShortText
encodeShort = forall a. (IPv4 -> a) -> (IPv6 -> a) -> IP -> a
case_ IPv4 -> ShortText
IPv4.encodeShort IPv6 -> ShortText
IPv6.encodeShort

-- | Encode an 'IP' as a bounded bytearray builder.
--
-- >>> BB.run Nat.constant (boundedBuilderUtf8 (ipv4 192 168 2 14))
-- [0x31, 0x39, 0x32, 0x2e, 0x31, 0x36, 0x38, 0x2e, 0x32, 0x2e, 0x31, 0x34]
boundedBuilderUtf8 :: IP -> BB.Builder 39
boundedBuilderUtf8 :: IP -> Builder 39
boundedBuilderUtf8 = forall a. (IPv4 -> a) -> (IPv6 -> a) -> IP -> a
case_
  (\IPv4
y -> forall (m :: Nat) (n :: Nat). (m <= n) -> Builder m -> Builder n
BB.weaken forall (a :: Nat) (b :: Nat).
(IsLte (CmpNat a b) ~ 'True) =>
a <= b
Lte.constant (IPv4 -> Builder 15
IPv4.boundedBuilderUtf8 IPv4
y))
  IPv6 -> Builder 39
IPv6.boundedBuilderUtf8

-- | Decode an 'IP' from 'Text'.
--
--   >>> decode "10.0.0.25"
--   Just (ipv4 10 0 0 25)
--
--   >>> fmap isIPv4 (decode "10.0.0.25")
--   Just True
--
--   >>> decode "3124::dead:cafe:ff:fe00:1"
--   Just (ipv6 0x3124 0x0000 0x0000 0xdead 0xcafe 0x00ff 0xfe00 0x0001)
--
--   >>> fmap isIPv6 (decode "3124::dead:cafe:ff:fe00:1")
--   Just True
decode :: Text -> Maybe IP
decode :: Text -> Maybe IP
decode Text
t = case Text -> Maybe IPv4
IPv4.decode Text
t of
  Maybe IPv4
Nothing -> case Text -> Maybe IPv6
IPv6.decode Text
t of
    Maybe IPv6
Nothing -> forall a. Maybe a
Nothing
    Just IPv6
v6 -> forall a. a -> Maybe a
Just (IPv6 -> IP
fromIPv6 IPv6
v6)
  Just IPv4
v4 -> forall a. a -> Maybe a
Just (IPv4 -> IP
fromIPv4 IPv4
v4)

-- | Decode an 'IP' from 'ShortText'.
--
--   >>> decodeShort "10.0.0.25"
--   Just (ipv4 10 0 0 25)
--   >>> decodeShort "::dead:cafe"
--   Just (ipv6 0x0000 0x0000 0x0000 0x0000 0x0000 0x0000 0xdead 0xcafe)
decodeShort :: ShortText -> Maybe IP
decodeShort :: ShortText -> Maybe IP
decodeShort ShortText
t
  | Just IPv4
x <- ShortText -> Maybe IPv4
IPv4.decodeShort ShortText
t = forall a. a -> Maybe a
Just (IPv4 -> IP
fromIPv4 IPv4
x)
  | Bool
otherwise = coerce :: forall a b. Coercible a b => a -> b
coerce (ShortText -> Maybe IPv6
IPv6.decodeShort ShortText
t)

-- | Decode UTF-8-encoded 'Bytes' into an 'IP' address.
decodeUtf8Bytes :: Bytes.Bytes -> Maybe IP
decodeUtf8Bytes :: Bytes -> Maybe IP
decodeUtf8Bytes !Bytes
b = case forall e a. (forall s. Parser e s a) -> Bytes -> Result e a
Parser.parseBytes (forall e s. e -> Parser e s IP
parserUtf8Bytes ()) Bytes
b of
  Parser.Success (Parser.Slice Int
_ Int
len IP
addr) -> case Int
len of
    Int
0 -> forall a. a -> Maybe a
Just IP
addr
    Int
_ -> forall a. Maybe a
Nothing
  Parser.Failure ()
_ -> forall a. Maybe a
Nothing

-- | Parse UTF-8-encoded 'Bytes' as an 'IP' address.
parserUtf8Bytes :: e -> Parser.Parser e s IP
parserUtf8Bytes :: forall e s. e -> Parser e s IP
parserUtf8Bytes e
e =
  forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap IPv4 -> IP
fromIPv4 (forall e s. e -> Parser e s IPv4
IPv4.parserUtf8Bytes ())
  forall x s a e. Parser x s a -> Parser e s a -> Parser e s a
`Parser.orElse`
  coerce :: forall a b. Coercible a b => a -> b
coerce (forall e s. e -> Parser e s IPv6
IPv6.parserUtf8Bytes e
e)

-- | Is the 'IP' an IPv4 address?
--
--   >>> isIPv4 (ipv4 10 0 0 25)
--   True
--
--   >>> isIPv4 (ipv6 0x3124 0x0 0x0 0xDEAD 0xCAFE 0xFF 0xFE00 0x1)
--   False
isIPv4 :: IP -> Bool
isIPv4 :: IP -> Bool
isIPv4 = forall a. (IPv4 -> a) -> (IPv6 -> a) -> IP -> a
case_ (forall a b. a -> b -> a
const Bool
True) (forall a b. a -> b -> a
const Bool
False)
{-# inline isIPv4 #-}

-- | Is the 'IP' an IPv6 address?
--
--   >>> isIPv6 (ipv4 10 0 0 25)
--   False
--
--   >>> isIPv6 (ipv6 0x3124 0x0 0x0 0xDEAD 0xCAFE 0xFF 0xFE00 0x1)
--   True
isIPv6 :: IP -> Bool
isIPv6 :: IP -> Bool
isIPv6 = forall a. (IPv4 -> a) -> (IPv6 -> a) -> IP -> a
case_ (forall a b. a -> b -> a
const Bool
False) (forall a b. a -> b -> a
const Bool
True)
{-# inline isIPv6 #-}

-- | Print an 'IP' using the textual encoding. This exists mostly for
--   debugging purposes.
--
--   >>> print (ipv4 10 0 0 25)
--   10.0.0.25
--
--   >>> print (ipv6 0x3124 0x0 0x0 0xDEAD 0xCAFE 0xFF 0xFE00 0x1)
--   3124::dead:cafe:ff:fe00:1
print :: IP -> IO ()
print :: IP -> IO ()
print = Text -> IO ()
TIO.putStrLn forall b c a. (b -> c) -> (a -> b) -> a -> c
. IP -> Text
encode

-- | A 32-bit 'IPv4' address or a 128-bit 'IPv6' address. Internally, this
--   is just represented as an 'IPv6' address. The functions provided
--   in @Net.IP@ help simulate constructing and pattern matching on values
--   of this type. All functions and typeclass methods that convert
--   'IP' values to text will display it as an 'IPv4' address if possible.
newtype IP = IP { IP -> IPv6
getIP :: IPv6 }
  deriving stock (IP -> IP -> Bool
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
/= :: IP -> IP -> Bool
$c/= :: IP -> IP -> Bool
== :: IP -> IP -> Bool
$c== :: IP -> IP -> Bool
Eq,Eq IP
IP -> IP -> Bool
IP -> IP -> Ordering
IP -> IP -> IP
forall a.
Eq a
-> (a -> a -> Ordering)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> Bool)
-> (a -> a -> a)
-> (a -> a -> a)
-> Ord a
min :: IP -> IP -> IP
$cmin :: IP -> IP -> IP
max :: IP -> IP -> IP
$cmax :: IP -> IP -> IP
>= :: IP -> IP -> Bool
$c>= :: IP -> IP -> Bool
> :: IP -> IP -> Bool
$c> :: IP -> IP -> Bool
<= :: IP -> IP -> Bool
$c<= :: IP -> IP -> Bool
< :: IP -> IP -> Bool
$c< :: IP -> IP -> Bool
compare :: IP -> IP -> Ordering
$ccompare :: IP -> IP -> Ordering
Ord,forall x. Rep IP x -> IP
forall x. IP -> Rep IP x
forall a.
(forall x. a -> Rep a x) -> (forall x. Rep a x -> a) -> Generic a
$cto :: forall x. Rep IP x -> IP
$cfrom :: forall x. IP -> Rep IP x
Generic,Ord IP
(IP, IP) -> Int
(IP, IP) -> [IP]
(IP, IP) -> IP -> Bool
(IP, IP) -> IP -> Int
forall a.
Ord a
-> ((a, a) -> [a])
-> ((a, a) -> a -> Int)
-> ((a, a) -> a -> Int)
-> ((a, a) -> a -> Bool)
-> ((a, a) -> Int)
-> ((a, a) -> Int)
-> Ix a
unsafeRangeSize :: (IP, IP) -> Int
$cunsafeRangeSize :: (IP, IP) -> Int
rangeSize :: (IP, IP) -> Int
$crangeSize :: (IP, IP) -> Int
inRange :: (IP, IP) -> IP -> Bool
$cinRange :: (IP, IP) -> IP -> Bool
unsafeIndex :: (IP, IP) -> IP -> Int
$cunsafeIndex :: (IP, IP) -> IP -> Int
index :: (IP, IP) -> IP -> Int
$cindex :: (IP, IP) -> IP -> Int
range :: (IP, IP) -> [IP]
$crange :: (IP, IP) -> [IP]
Ix,Typeable IP
IP -> DataType
IP -> Constr
(forall b. Data b => b -> b) -> IP -> IP
forall a.
Typeable a
-> (forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> a -> c a)
-> (forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c a)
-> (a -> Constr)
-> (a -> DataType)
-> (forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c a))
-> (forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a))
-> ((forall b. Data b => b -> b) -> a -> a)
-> (forall r r'.
    (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
-> (forall r r'.
    (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
-> (forall u. (forall d. Data d => d -> u) -> a -> [u])
-> (forall u. Int -> (forall d. Data d => d -> u) -> a -> u)
-> (forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> a -> m a)
-> (forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> a -> m a)
-> (forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> a -> m a)
-> Data a
forall u. Int -> (forall d. Data d => d -> u) -> IP -> u
forall u. (forall d. Data d => d -> u) -> IP -> [u]
forall r r'.
(r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> IP -> r
forall r r'.
(r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> IP -> r
forall (m :: * -> *).
Monad m =>
(forall d. Data d => d -> m d) -> IP -> m IP
forall (m :: * -> *).
MonadPlus m =>
(forall d. Data d => d -> m d) -> IP -> m IP
forall (c :: * -> *).
(forall b r. Data b => c (b -> r) -> c r)
-> (forall r. r -> c r) -> Constr -> c IP
forall (c :: * -> *).
(forall d b. Data d => c (d -> b) -> d -> c b)
-> (forall g. g -> c g) -> IP -> c IP
forall (t :: * -> *) (c :: * -> *).
Typeable t =>
(forall d. Data d => c (t d)) -> Maybe (c IP)
forall (t :: * -> * -> *) (c :: * -> *).
Typeable t =>
(forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c IP)
gmapMo :: forall (m :: * -> *).
MonadPlus m =>
(forall d. Data d => d -> m d) -> IP -> m IP
$cgmapMo :: forall (m :: * -> *).
MonadPlus m =>
(forall d. Data d => d -> m d) -> IP -> m IP
gmapMp :: forall (m :: * -> *).
MonadPlus m =>
(forall d. Data d => d -> m d) -> IP -> m IP
$cgmapMp :: forall (m :: * -> *).
MonadPlus m =>
(forall d. Data d => d -> m d) -> IP -> m IP
gmapM :: forall (m :: * -> *).
Monad m =>
(forall d. Data d => d -> m d) -> IP -> m IP
$cgmapM :: forall (m :: * -> *).
Monad m =>
(forall d. Data d => d -> m d) -> IP -> m IP
gmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> IP -> u
$cgmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> IP -> u
gmapQ :: forall u. (forall d. Data d => d -> u) -> IP -> [u]
$cgmapQ :: forall u. (forall d. Data d => d -> u) -> IP -> [u]
gmapQr :: forall r r'.
(r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> IP -> r
$cgmapQr :: forall r r'.
(r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> IP -> r
gmapQl :: forall r r'.
(r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> IP -> r
$cgmapQl :: forall r r'.
(r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> IP -> r
gmapT :: (forall b. Data b => b -> b) -> IP -> IP
$cgmapT :: (forall b. Data b => b -> b) -> IP -> IP
dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
Typeable t =>
(forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c IP)
$cdataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
Typeable t =>
(forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c IP)
dataCast1 :: forall (t :: * -> *) (c :: * -> *).
Typeable t =>
(forall d. Data d => c (t d)) -> Maybe (c IP)
$cdataCast1 :: forall (t :: * -> *) (c :: * -> *).
Typeable t =>
(forall d. Data d => c (t d)) -> Maybe (c IP)
dataTypeOf :: IP -> DataType
$cdataTypeOf :: IP -> DataType
toConstr :: IP -> Constr
$ctoConstr :: IP -> Constr
gunfold :: forall (c :: * -> *).
(forall b r. Data b => c (b -> r) -> c r)
-> (forall r. r -> c r) -> Constr -> c IP
$cgunfold :: forall (c :: * -> *).
(forall b r. Data b => c (b -> r) -> c r)
-> (forall r. r -> c r) -> Constr -> c IP
gfoldl :: forall (c :: * -> *).
(forall d b. Data d => c (d -> b) -> d -> c b)
-> (forall g. g -> c g) -> IP -> c IP
$cgfoldl :: forall (c :: * -> *).
(forall d b. Data d => c (d -> b) -> d -> c b)
-> (forall g. g -> c g) -> IP -> c IP
Data)
  deriving newtype (Eq IP
Int -> IP -> Int
IP -> Int
forall a. Eq a -> (Int -> a -> Int) -> (a -> Int) -> Hashable a
hash :: IP -> Int
$chash :: IP -> Int
hashWithSalt :: Int -> IP -> Int
$chashWithSalt :: Int -> IP -> Int
Hashable)

instance NFData IP

instance Show IP where
  showsPrec :: Int -> IP -> ShowS
showsPrec Int
p = forall a. (IPv4 -> a) -> (IPv6 -> a) -> IP -> a
case_ (forall a. Show a => Int -> a -> ShowS
showsPrec Int
p) (forall a. Show a => Int -> a -> ShowS
showsPrec Int
p)

instance Read IP where
  readPrec :: ReadPrec IP
readPrec = forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap IPv4 -> IP
fromIPv4 forall a. Read a => ReadPrec a
readPrec forall a. ReadPrec a -> ReadPrec a -> ReadPrec a
+++ forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap IPv6 -> IP
fromIPv6 forall a. Read a => ReadPrec a
readPrec

instance ToJSON IP where
  toJSON :: IP -> Value
toJSON = Text -> Value
Aeson.String forall b c a. (b -> c) -> (a -> b) -> a -> c
. IP -> Text
encode

instance FromJSON IP where
  parseJSON :: Value -> Parser IP
parseJSON = forall a. String -> (Text -> Parser a) -> Value -> Parser a
Aeson.withText String
"IP" forall a b. (a -> b) -> a -> b
$ \Text
t -> case Text -> Maybe IP
decode Text
t of
    Maybe IP
Nothing -> forall (m :: * -> *) a. MonadFail m => String -> m a
fail String
"Could not parse IP address"
    Just IP
addr -> forall (m :: * -> *) a. Monad m => a -> m a
return IP
addr