From: Michael Orlitzky <michael@orlitzky.com>
Date: Sun, 2 May 2010 19:19:00 +0000 (-0400)
Subject: Add a None constructor for Octets.
X-Git-Tag: 0.0.1~81
X-Git-Url: https://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=d4f46f4d52b3d51c2eb59a4aa818d4f23f14203d;p=hath.git

Add a None constructor for Octets.
Return Octet.None when an octet is created from an invalid Int.
---

diff --git a/src/Octet.hs b/src/Octet.hs
index f8af4df..e0a4bf6 100644
--- a/src/Octet.hs
+++ b/src/Octet.hs
@@ -5,14 +5,14 @@ import Bit
 -- An Octet consists of eight bits. For our purposes, the most
 -- significant bit will come "first." That is, b1 is in the 2^7
 -- place while b8 is in the 2^0 place.
-data Octet = Octet { b1 :: Bit,
-                     b2 :: Bit,
-                     b3 :: Bit,
-                     b4 :: Bit,
-                     b5 :: Bit,
-                     b6 :: Bit,
-                     b7 :: Bit,
-                     b8 :: Bit }
+data Octet = None | Octet { b1 :: Bit,
+                            b2 :: Bit,
+                            b3 :: Bit,
+                            b4 :: Bit,
+                            b5 :: Bit,
+                            b6 :: Bit,
+                            b7 :: Bit,
+                            b8 :: Bit }
            deriving (Eq, Show)
 
 -- Convert each bit to its integer value, and multiply by the
@@ -30,10 +30,10 @@ octet_to_int x =
     0   * (bit_to_int (b8 x))
 
 
--- Supply an integer greater than 255 at your own risk.
+
 octet_from_int :: Int -> Octet
 octet_from_int x
-    | (x < 0) = min_octet 
+    | (x < 0) || (x > 255) = Octet.None
     | otherwise = (Octet a1 a2 a3 a4 a5 a6 a7 a8)
     where
       a1 = if (x `mod` 128) > 0 then One else Zero