Chapter 3 Daily 05 HW

Some longer example tests are available. Additional example showing how to read a bunch of lyrics from a file (for a cool thing to encrypt in problem 8).

How many numbers are between two given binary numbers, including the start and end number?
```
 bcount :: [Int] -> [Int] -> Int
 bcount [1,0,0,1,1] [1,1,0,1,0] == 8
```
(ensureLen :: Int -> [Int] -> [Int]). The call ensureLen 6 xs add leading zeros to xs if necessary to ensure it has a length of at least 6.
```
 ensureLen 4 [1] == [0,0,0,1]
 ensureLen 3 [1,0,1,0,1] == [1,0,1,0,1]
```
(and' :: Int -> Int -> Int). Helper function. Give 1 if both inputs are 1, otherwise 0.
(bitwiseAnd) Given two binary integers a and b (represented as lists of 0 and 1), produce the binary number given by lining up the ones places and the then “and”-ing the digits of a and b together. The shorter number should be padded with zeros to be the same length as the long number.
(bitwise) Given a binary operation (op :: Int -> Int -> Int) and two binary integers, create a number by performing the operation bitwise as in the previous exercise. The shorter number should be padded with zeros to be the same length as the long number.

The type signature for op in the big bitwise signature is (Int->Int->Int). Example:
```
 xor' :: Int -> Int -> Int
 xor' a b = if a == b then 0 else 1

 bitwise xor' [1,0,1,0] [0,1,1,0] = [1,1,0,0]
```
txtToBin :: String -> [[Int]]. Translate a string into a list of binary numbers using the location each character is found in the (abbreviated) list below. If a character is not found, produce the empty list to represent it.
```
 [space]A-Za-z0-9.
```
binToMsg :: [[Int]] -> [Int]. Make sure each binary number is 6 digits, and then concatenate all of the binary numbers into one long list of integers.
msgDecode :: [Int] -> String. Now decode the big binary number, changing it back into text.
encrypt :: String -> String -> String. The encrypt function takes in a message string and a key string. The encryption lines up the letters in the message and the string, changes the characters into binary numbers, joins the binary numbers with xor, and then changes the resulting number back into a string. The string will be nonsense.
```
 encrypt "Key" "Secret"
```
The key is repeated and lined up with the secret message, then the values of the binary numbers are combined with xor.
```
 "KeyKeyK"
 "Secrets"
 "X tm cl"
```
Note: this function is likely to require helper functions!
decrypt :: String -> String -> String. Given an encrypted message and a key, reverse the encryption process. This is kind of tricky without experimentation; try just re-encrypting the message and see if you can figure out a pattern.

Last modified August 25, 2021: ap-cs 2019-2020 (4d1c12c)