Add a None constructor for IPv4Address.

Hide the constructor for IPv4Address.
Created an ipv4address_from_octets function which mimics the constructor but will return IPv4Address.None in response to being passed Octet.Nones.

diff --git a/src/IPv4Address.hs b/src/IPv4Address.hs
index 3d6b1bbc2980107ae15d3d9da3ccd521b5cd2c9c..7c5d80deb6d00fd60a324fa82a916aaff233317f 100644 (file)
--- a/src/IPv4Address.hs
+++ b/src/IPv4Address.hs
@@ -1,17 +1,43 @@
-module IPv4Address where
+module IPv4Address
+( ipv4address_from_octets,
+  IPv4Address(None),
+  Maskbits,
+  max_octet1,
+  max_octet2,
+  max_octet3,
+  max_octet4,
+  min_octet1,
+  min_octet2,
+  min_octet3,
+  min_octet4
+)
+  where
 
 import Bit
 import Octet
 
 type Maskbits = Int
 
-data IPv4Address = IPv4Address { octet1 :: Octet,
-                                 octet2 :: Octet,
-                                 octet3 :: Octet,
-                                 octet4 :: Octet }
+data IPv4Address = None | IPv4Address { octet1 :: Octet,
+                                        octet2 :: Octet,
+                                        octet3 :: Octet,
+                                        octet4 :: Octet }
                  deriving (Eq, Show)
 
 
+-- We don't export our constructor so this function is the only
+-- way to construct an address from octets. As a result, we can
+-- return IPv4Address.None in response to being passed one of more
+-- Octet.None octets.
+ipv4address_from_octets :: Octet -> Octet -> Octet -> Octet -> IPv4Address
+ipv4address_from_octets oct1 oct2 oct3 oct4
+    | or [oct1 == Octet.None,
+          oct2 == Octet.None,
+          oct3 == Octet.None,
+          oct4 == Octet.None] = IPv4Address.None
+    | otherwise = IPv4Address oct1 oct2 oct3 oct4
+
+
 min_address :: IPv4Address -> Maskbits -> IPv4Address
 min_address addr mask
     | mask == 32 = IPv4Address oct1 oct2 oct3 oct4