X-Git-Url: http://gitweb.michael.orlitzky.com/?p=hath.git;a=blobdiff_plain;f=src%2FOctet.hs;h=c472f8da6e8c85552c32256f5409e0daeb86c5b8;hp=574edc435a90f4f50a860b118e96ef0f75c9a32f;hb=45ac9baca360d0f0dabe4576fb44c1634a50dbf7;hpb=18a81546e7c4ad10574918efb08b2e104e911d73

diff --git a/src/Octet.hs b/src/Octet.hs
index 574edc4..c472f8d 100644
--- a/src/Octet.hs
+++ b/src/Octet.hs
@@ -1,21 +1,19 @@
 module Octet (
   Octet(..),
-  octet_from_int,
   octet_properties,
   octet_tests,
   )
 where
 
-import Data.Maybe (fromJust)
 import Test.HUnit (assertEqual)
 import Test.Framework (Test, testGroup)
 import Test.Framework.Providers.HUnit (testCase)
 import Test.Framework.Providers.QuickCheck2 (testProperty)
 import Test.QuickCheck (Arbitrary(..), Gen, Property, (==>))
 
-import Bit as B
-import Maskable
-import Maskbits
+import Bit as B (Bit(..))
+import Maskable (Maskable(..))
+import Maskbits (Maskbits(..))
 
 -- | An Octet consists of eight bits. For our purposes, the most
 --   significant bit will come "first." That is, b1 is in the 2^7
@@ -106,48 +104,47 @@ instance Bounded Octet where
 
 
 instance Enum Octet where
-  -- We're supposed to throw a runtime error if you call (succ
-  -- maxBound), so the fromJust here doesn't introduce any additional
-  -- badness.
-  toEnum = fromJust . octet_from_int
+
+  -- | Create an 'Octet' from an 'Int'. The docs for Enum say we
+  --   should throw a runtime error on out-of-bounds, so we do.
+  toEnum x
+    | x < minBound || x > maxBound = error "octet out of bounds"
+    | otherwise = Octet a1 a2 a3 a4 a5 a6 a7 a8
+        where
+          a1 = if (x >= 128) then B.One else B.Zero
+          a2 = if ((x `mod` 128) >= 64) then B.One else B.Zero
+          a3 = if ((x `mod` 64)  >= 32) then B.One else B.Zero
+          a4 = if ((x `mod` 32)  >= 16) then B.One else B.Zero
+          a5 = if ((x `mod` 16)  >= 8)  then B.One else B.Zero
+          a6 = if ((x `mod` 8)   >= 4)  then B.One else B.Zero
+          a7 = if ((x `mod` 4)   >= 2)  then B.One else B.Zero
+          a8 = if ((x `mod` 2)   == 1)  then B.One else B.Zero
 
   -- | Convert each bit to its integer value, and multiply by the
   --   appropriate power of two. Sum them up, and we should get an integer
   --   between 0 and 255.
   fromEnum x =
-    128 * (bit_to_int (b1 x)) +
-    64  * (bit_to_int (b2 x)) +
-    32  * (bit_to_int (b3 x)) +
-    16  * (bit_to_int (b4 x)) +
-    8   * (bit_to_int (b5 x)) +
-    4   * (bit_to_int (b6 x)) +
-    2   * (bit_to_int (b7 x)) +
-    1   * (bit_to_int (b8 x))
-
+    128 * (fromEnum (b1 x)) +
+    64  * (fromEnum (b2 x)) +
+    32  * (fromEnum (b3 x)) +
+    16  * (fromEnum (b4 x)) +
+    8   * (fromEnum (b5 x)) +
+    4   * (fromEnum (b6 x)) +
+    2   * (fromEnum (b7 x)) +
+    1   * (fromEnum (b8 x))
 
 
-octet_from_int :: Int -> Maybe Octet
-octet_from_int x
-  | (x < 0) || (x > 255) = Nothing
-  | otherwise = Just (Octet a1 a2 a3 a4 a5 a6 a7 a8)
-  where
-    a1 = if (x >= 128) then B.One else B.Zero
-    a2 = if ((x `mod` 128) >= 64) then B.One else B.Zero
-    a3 = if ((x `mod` 64)  >= 32) then B.One else B.Zero
-    a4 = if ((x `mod` 32)  >= 16) then B.One else B.Zero
-    a5 = if ((x `mod` 16)  >= 8)  then B.One else B.Zero
-    a6 = if ((x `mod` 8)   >= 4)  then B.One else B.Zero
-    a7 = if ((x `mod` 4)   >= 2)  then B.One else B.Zero
-    a8 = if ((x `mod` 2)   == 1)  then B.One else B.Zero
-
 
 instance Read Octet where
   readsPrec _ = \s ->
     case (reads s :: [(Int, String)]) of
       []              -> []
-      (x,leftover):_  -> case (octet_from_int x) of
-                           Nothing -> []
-                           Just oct -> [(oct, leftover)]
+      (x,leftover):_  -> go x leftover
+    where
+      go :: Int -> String -> [(Octet, String)]
+      go y s
+        | y < minBound || y > maxBound = []
+        | otherwise = [(toEnum y, s)]
 
 
 -- Test lists.
@@ -192,7 +189,7 @@ test_octet_from_int1 =
   where
     desc = "octet_from_int 128 should parse as 10000000"
     oct1 = Octet B.One B.Zero B.Zero B.Zero B.Zero B.Zero B.Zero B.Zero
-    oct2 = fromJust $ octet_from_int 128
+    oct2 = toEnum 128
 
 test_octet_mask1 :: Test
 test_octet_mask1 =
@@ -200,8 +197,8 @@ test_octet_mask1 =
     assertEqual desc oct2 (apply_mask oct1 Four B.Zero)
   where
     desc = "The network bits of 255/4 should equal 240"
-    oct1 = fromJust $ octet_from_int 255
-    oct2 = fromJust $ octet_from_int 240
+    oct1 = toEnum 255
+    oct2 = toEnum 240 :: Octet
 
 
 test_octet_mask2 :: Test
@@ -210,5 +207,5 @@ test_octet_mask2 =
     assertEqual desc oct2 (apply_mask oct1 Maskbits.One B.Zero)
   where
     desc = "The network bits of 255/1 should equal 128"
-    oct1 = fromJust $ octet_from_int 255
-    oct2 = fromJust $ octet_from_int 128
+    oct1 = toEnum 255
+    oct2 = toEnum 128 :: Octet