Greatly simplify the definition of IPv4Address.apply_mask.

diff --git a/src/IPv4Address.hs b/src/IPv4Address.hs
index 6153d282a681305bdcd8a83848ebe16ed40de9ba..b46f18c453ea967d19291810cd824a546975f5c9 100644 (file)
--- a/src/IPv4Address.hs
+++ b/src/IPv4Address.hs
@@ -46,93 +46,122 @@ instance Arbitrary IPv4Address where
 
 instance Maskable IPv4Address where
 
-  apply_mask addr mask bit
-      | mask == ThirtyTwo = addr
-      | mask == ThirtyOne = addr { octet4 = (apply_mask oct4 Seven bit) }
-      | mask == Thirty = addr { octet4 = (apply_mask oct4 Six bit) }
-      | mask == TwentyNine = addr { octet4 = (apply_mask oct4 Five bit) }
-      | mask == TwentyEight = addr { octet4 = (apply_mask oct4 Four bit) }
-      | mask == TwentySeven = addr { octet4 = (apply_mask oct4 Three bit) }
-      | mask == TwentySix = addr { octet4 = (apply_mask oct4 Two bit) }
-      | mask == TwentyFive = addr { octet4 = (apply_mask oct4 One bit) }
-      | mask == TwentyFour = addr { octet4 = (apply_mask oct4 Zero bit) }
-      | mask == TwentyThree = addr { octet3 = (apply_mask oct3 Seven bit),
-                                    octet4 = (apply_mask oct4 Zero bit) }
-      | mask == TwentyTwo = addr { octet3 = (apply_mask oct3 Six bit),
-                                  octet4 = (apply_mask oct4 Zero bit) }
-      | mask == TwentyOne = addr { octet3 = (apply_mask oct3 Five bit),
-                                  octet4 = (apply_mask oct4 Zero bit) }
-      | mask == Twenty = addr { octet3 = (apply_mask oct3 Four bit),
-                               octet4 = (apply_mask oct4 Zero bit) }
-      | mask == Nineteen = addr { octet3 = (apply_mask oct3 Three bit),
-                                 octet4 = (apply_mask oct4 Zero bit) }
-      | mask == Eighteen = addr { octet3 = (apply_mask oct3 Two bit),
-                                 octet4 = (apply_mask oct4 Zero bit) }
-      | mask == Seventeen = addr { octet3 = (apply_mask oct3 One bit),
-                                  octet4 = (apply_mask oct4 Zero bit) }
-      | mask == Sixteen = addr { octet3 = (apply_mask oct3 Zero bit),
-                                octet4 = (apply_mask oct4 Zero bit) }
-      | mask == Fifteen = addr { octet2 = (apply_mask oct2 Seven bit),
-                                octet3 = (apply_mask oct3 Zero bit),
-                                octet4 = (apply_mask oct4 Zero bit) }
-      | mask == Fourteen = addr { octet2 = (apply_mask oct2 Six bit),
-                                 octet3 = (apply_mask oct3 Zero bit),
-                                 octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Thirteen = addr { octet2 = (apply_mask oct2 Five bit),
-                                 octet3 = (apply_mask oct3 Zero bit),
-                                 octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Twelve = addr { octet2 = (apply_mask oct2 Four bit),
-                               octet3 = (apply_mask oct3 Zero bit),
-                               octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Eleven = addr { octet2 = (apply_mask oct2 Three bit),
-                               octet3 = (apply_mask oct3 Zero bit),
-                               octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Ten = addr { octet2 = (apply_mask oct2 Two bit),
-                            octet3 = (apply_mask oct3 Zero bit),
-                            octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Nine = addr { octet2 = (apply_mask oct2 One bit),
-                             octet3 = (apply_mask oct3 Zero bit),
-                             octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Eight = addr { octet2 = (apply_mask oct2 Zero bit),
-                              octet3 = (apply_mask oct3 Zero bit),
-                              octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Seven = addr { octet1 = (apply_mask oct1 Seven bit),
-                              octet2 = (apply_mask oct2 Zero bit),
-                              octet3 = (apply_mask oct3 Zero bit),
-                              octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Six = addr { octet1 = (apply_mask oct1 Six bit),
-                            octet2 = (apply_mask oct2 Zero bit),
-                            octet3 = (apply_mask oct3 Zero bit),
-                            octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Five = addr { octet1 = (apply_mask oct1 Five bit),
-                             octet2 = (apply_mask oct2 Zero bit),
-                             octet3 = (apply_mask oct3 Zero bit),
-                             octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Four = addr { octet1 = (apply_mask oct1 Four bit),
-                             octet2 = (apply_mask oct2 Zero bit),
-                             octet3 = (apply_mask oct3 Zero bit),
-                             octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Three = addr { octet1 = (apply_mask oct1 Three bit),
-                              octet2 = (apply_mask oct2 Zero bit),
-                              octet3 = (apply_mask oct3 Zero bit),
-                              octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Two = addr { octet1 = (apply_mask oct1 Two bit),
-                            octet2 = (apply_mask oct2 Zero bit),
-                            octet3 = (apply_mask oct3 Zero bit),
-                            octet4 = (apply_mask oct4 Zero bit)}
-      | mask == One = addr { octet1 = (apply_mask oct1 One bit),
-                            octet2 = (apply_mask oct2 Zero bit),
-                            octet3 = (apply_mask oct3 Zero bit),
-                            octet4 = (apply_mask oct4 Zero bit)}
-      | mask == Zero = addr { octet1 = (apply_mask oct1 Zero bit),
-                             octet2 = (apply_mask oct2 Zero bit),
-                             octet3 = (apply_mask oct3 Zero bit),
-                             octet4 = (apply_mask oct4 Zero bit)}
-      where
-        oct1 = (octet1 addr)
-        oct2 = (octet2 addr)
-        oct3 = (octet3 addr)
-        oct4 = (octet4 addr)
+  apply_mask addr mask bit =
+   apply_mask' mask
+   where
+     oct1 = octet1 addr
+     oct2 = octet2 addr
+     oct3 = octet3 addr
+     oct4 = octet4 addr
+
+     -- A copy of 'addr' with the fourth octet zeroed (or oned).
+     new_addr1 = addr { octet4 = (apply_mask oct4 Zero bit) }
+
+     -- Likewise for new_addr1's third octet.
+     new_addr2 = new_addr1 { octet3 = (apply_mask oct3 Zero bit) }
+
+     -- And new_addr2's second octet.
+     new_addr3 = new_addr2 { octet2 = (apply_mask oct2 Zero bit) }
+
+     -- This helper function allows us to pattern-match cleanly.
+     apply_mask' :: Maskbits -> IPv4Address
+
+     apply_mask' ThirtyTwo = addr
+
+     apply_mask' ThirtyOne = addr { octet4 = (apply_mask oct4 Seven bit) }
+
+     apply_mask' Thirty =
+       addr { octet4 = (apply_mask oct4 Six bit) }
+
+     apply_mask' TwentyNine =
+       addr { octet4 = (apply_mask oct4 Five bit) }
+
+     apply_mask' TwentyEight =
+       addr { octet4 = (apply_mask oct4 Four bit) }
+
+     apply_mask' TwentySeven =
+       addr { octet4 = (apply_mask oct4 Three bit) }
+
+     apply_mask' TwentySix =
+       addr { octet4 = (apply_mask oct4 Two bit) }
+
+     apply_mask' TwentyFive =
+       addr { octet4 = (apply_mask oct4 One bit) }
+
+     apply_mask' TwentyFour = new_addr1
+
+     apply_mask' TwentyThree =
+       new_addr1 { octet3 = (apply_mask oct3 Seven bit) }
+
+     apply_mask' TwentyTwo =
+       new_addr1 { octet3 = (apply_mask oct3 Six bit) }
+
+     apply_mask' TwentyOne =
+       new_addr1 { octet3 = (apply_mask oct3 Five bit) }
+
+     apply_mask' Twenty =
+       new_addr1 { octet3 = (apply_mask oct3 Four bit) }
+
+     apply_mask' Nineteen =
+       new_addr1 { octet3 = (apply_mask oct3 Three bit) }
+
+     apply_mask' Eighteen =
+       new_addr1 { octet3 = (apply_mask oct3 Two bit) }
+
+     apply_mask' Seventeen =
+       new_addr1 { octet3 = (apply_mask oct3 One bit) }
+
+     apply_mask' Sixteen =
+       new_addr2
+
+     apply_mask' Fifteen =
+       new_addr2 { octet2 = (apply_mask oct2 Seven bit) }
+
+     apply_mask' Fourteen =
+       new_addr2 { octet2 = (apply_mask oct2 Six bit) }
+
+     apply_mask' Thirteen =
+       new_addr2 { octet2 = (apply_mask oct2 Five bit) }
+
+     apply_mask' Twelve =
+       new_addr2 { octet2 = (apply_mask oct2 Four bit) }
+
+     apply_mask' Eleven =
+       new_addr2 { octet2 = (apply_mask oct2 Three bit) }
+
+     apply_mask' Ten =
+       new_addr2 { octet2 = (apply_mask oct2 Two bit) }
+
+     apply_mask' Nine =
+       new_addr2 { octet2 = (apply_mask oct2 One bit) }
+
+     apply_mask' Eight =
+       new_addr3 { octet2 = (apply_mask oct2 Zero bit) }
+
+     apply_mask' Seven =
+       new_addr3 { octet1 = (apply_mask oct1 Seven bit) }
+
+     apply_mask' Six =
+       new_addr3 { octet1 = (apply_mask oct1 Six bit) }
+
+     apply_mask' Five =
+       new_addr3 { octet1 = (apply_mask oct1 Five bit) }
+
+     apply_mask' Four =
+       new_addr3 { octet1 = (apply_mask oct1 Four bit) }
+
+     apply_mask' Three =
+       new_addr3 { octet1 = (apply_mask oct1 Three bit) }
+
+     apply_mask' Two =
+       new_addr3 { octet1 = (apply_mask oct1 Two bit) }
+
+     apply_mask' One =
+       new_addr3 { octet1 = (apply_mask oct1 One bit) }
+
+     apply_mask' Zero =
+       new_addr3 { octet1 = (apply_mask oct1 Zero bit) }
+
 
 
 -- | The minimum possible IPv4 address, 0.0.0.0.