Purpose of this assignment

To get you started programming functionally in Scala.

General idea

Implement the Playfair Cipher (see the Wikipedia article) for enciphering and deciphering messages. Use this variant:

• The cipher table is filled in left to right, top to bottom.
• Any 'j' in the input will be replaced by 'i'.
• If a double letter occurs in a pair, an 'x' will be inserted between them.
  • Example: "te ll in g" -> "te lx li ng", but "op po se" does not get an x inserted.
  • Exception: If a pair is "xx", insert a 'q' between them.
• If a final letter is needed to complete a pair, use 'z'.

Assignment details

Here is an example input to be encoded:

An anonymous reader sends word of a proof-of-concept Google Chrome browser
extension that steals users' login details. The developer, Andreas Grech,
says that he is trying to raise awareness about security among end users,
and therefore chose Chrome as a test-bed because of its reputation as the
safest browser.

With keyword "Pennsylvania", here is the code block:

p	e	n	s	y
l	v	a	i	b
c	d	f	g	h
k	m	o	q	r
t	u	w	x	z

Here is an example encoded output:

fafaw aermw yqnvm vqyns genwm hwoln kqwow ofkpf nexcq wqfvp
dckqu vhzwn ynmyz unsig wazcl wpxnv ipxey mpiqf asmvw lbvpx
dymvd vaken obefm yinhq pdgyb npxfb zcsvp xzbas cxqki bynfn
bonsn yniar wuynd tqbzp vowad sefxe ymnie fzcym ndqkp dfryn
dckqu vinlw nyzlv mvyfl xenmg axpmy etwlx lwain zcnyf onyzl
kqxny m

Program structure

• Project name: Playfair
  • Package name: playfair
    • object Playfair
      • def main(args: Array[String])
        • The main method will interact with the user: It will ask whether to encode, decode, or quit; then (unless quitting) it will ask for the keyword, then it will ask for the name of a file to be encoded/decoded. It will read in the file, encode or decode it, and display the result, ten blocks per line. This should be repeated until the user quits the program.
    • class Coder(keyword: String)
      • def encode(plainText: String): String
        • The encode method will take a single String of arbitrary text. It will be mixed case, with spaces, newlines, and punctuation marks. The return value should be all lowercase; letters should be blocks of 5, with a single space between blocks. The last block may contain fewer than 5 characters. There should be no whitespace at the beginning or the end, and only a single space between blocks. All the punctuation should be discarded.
      • def decode(secretText: String): String
        • Text to be decoded will be in the format produced by the encoder. After decoding, an x between double letters (for example, nxn) should be removed, and an xqx should be replaced with xx. The result should be put into the same format as the encoded text (blocks of five letters, whitespace as specified above). Do not attempt any other "improvements" (replacing i with j, inserting punctuation, etc.)

Use additional classes, objects, and methods as you see fit.

Special rules

• The base score for a properly working, properly formatted, and properly commented program will be 70 points.The maximum score will be 120.
• You will gain 1 point for each function defined with def, up to a maximum of 5 points.
• You will gain 2 points for each literal function defined with =>, up to a maximum of 10 points.
• You will gain 5 points for the first use of map, filter, foldLeft or /:, foldRight or :\, yield, and Some, and 2 points for each subsequent use of the same method, up to a maximum of 30 points.
• You will gain 5 points if your program uses at least one match.
• You will lose all the extra points if we think you are just throwing in some of the above, without seriously trying to use them, just to get a few more points. Plus, we will get annoyed at you.
• You will lose 3 points for each occurrence of one of the keywords var and while, 5 points for each occurrence of Array (except in def main), and 10 points for each occurrence of null (except in a request for a file). This is to get you to use for, List, and maybe Some.

The reasons for these rules are twofold: (1) They are intended to get you using some of the unique Scala constructs, and (2) It is easy to write a program to count these keywords.

Due date

Zip your Scala project and submit it via Canvas by 6am Wednesday, November 25.