string_transmitter.hs

import Data.Char

type Bit = Int

-- in reverse order
bits2int :: [Bit] -> Int
bits2int bits = sum [w*b | (w,b) <- zip weights bits]
               where weights = iterate (*2) 1

int2bin :: Int -> [Bit]
int2bin 0 = []
int2bin n = n `mod` 2 : int2bin (n `div` 2)

-- truncates or extends a binary number to precisely eight bits
make8 :: [Bit] -> [Bit]
make8 bits = take 8 (bits ++ repeat 0)

encode :: String -> [Bit]
encode = concat.map (make8.int2bin.ord)

-- chops a list produce by encode into eight-bit binary numbers
chop8 :: [Bit] -> [[Bit]]
chop8 [] = []
chop8 bits = take 8 bits: chop8 (drop 8 bits)

decode :: [Bit] -> String
decode = map (chr.bits2int).chop8

-- simulates the transmission of a string of characters as a list of bits, using identity function to model a 
-- perfect communication channel
transmit :: String -> String
transmit = decode.channel.encode

channel :: [Bit] -> [Bit]
channel = id