Add a None constructor for Bits.

diff --git a/src/Bit.hs b/src/Bit.hs
index 1c7de7bf4169862cf791e8ebf6bd5e92751a4852..7c1840823b041774774f7d49519ff190f6f52033 100644 (file)
--- a/src/Bit.hs
+++ b/src/Bit.hs
@@ -1,15 +1,16 @@
 module Bit where
 
-data Bit = Zero | One
+data Bit = None | Zero | One
          deriving (Eq, Show)
 
 bit_to_int :: Bit -> Int
-bit_to_int Zero = 0
-bit_to_int One  = 1
+bit_to_int None = -1
+bit_to_int Zero =  0
+bit_to_int One  =  1
 
 -- If we are passed a '0' or '1', convert it appropriately. Otherwise,
--- default to Zero.
+-- default to None.
 bit_from_char :: Char -> Bit
 bit_from_char '0' = Zero
 bit_from_char '1' = One
-bit_from_char  _  = Zero
+bit_from_char  _  = None