Ch6 Quiz A

Please write your answers on paper and turn in the paper.

1. Explain in your own words what foldl is good for.

2. Use foldl to remove duplicates from a list. Write your own fold function. Example:

    undup [1,1,1,2,3,2] == [1,2,3]
   

3. You are going to hide a secret message inside a public message by inserting the letters of the secret message every given number (n) of the public message letters. If there are not enough letters in the public message, just put the unused part of the secret message at the end. Begin the output with part of the public message.

    steg "Whitney Young" "ABC" 4
      == "WhitAney BYounCg"
   
    steg "Whitney Young" "Long Message" 5
      == "WhitnLey Yooungng Message"
   

4. Write a decoder for messages like the first one, which are able to fit completely inside the second. Take in the number of letters between each secret letter.

    unsteg 4 "WhitAney BYounCg" == "ABC"