Kotlin and Functional Programming

Kotlin

I strongly encourage you to write and test in little pieces. For instance, in the final program, be sure you are clear about what the add function does with a MutableList. Functional programming encourages you to thing "bottom up" so start as small as you can and build on really small pieces.

Throughout this assignment you may not use loops or variables. By loop, I mean any construct like a for or while loop, that causes an action to be repeated within a function (this definition is intended to allow recursion.) By variable I mean any object whose value may change by means of assignment. So an object allocated with "val" would not be a variable as its value, once set, the pointer cannot be changed.

Associated with each part are one or more questions -- in bold face. Answer these questions in your README.

Part 1

Do not put the tailrec tag onto your function (yet).

Adjust your program by adding the keyword "tailrec" to the first line of the recursive function. (Also, make your function tail recursive if it was not already. That is, if the function was

    BEFORE
        fun printHW(va: Int) {
    AFTER
        tailrec fun printHW(va: Int) {
    

Nested Functions

    fun main() {
        val arr = arrayOf(arrayOf(1, 2, 3), arrayOf(4, 5, 6), arrayOf(7, 8, 9))
        val arrc = arrayOf(arrayOf('c', 'd', 'e'), arrayOf('g','h','i'), arrayOf('j','l','m','n'))
        val arrs = arrayOf(arrayOf("c", "d", "e", "A"), arrayOf("g","h","i"), arrayOf("j","l","m","n", "1", "2", "3"))
        
        printArr(arr)
        printArr(arrc)
        printArr(arrs)
    }    

1 2 3 
4 5 6 
7 8 9 

c d e 
g h i 
j l m n 

c d e A 
g h i 
j l m n 1 2 3 

• You may not use loops.
• Each item printed should be printed independently
• printArr itself should be recursive. Do not do the Java trick of having printArrUtil.
• You must use at least one parameter with a default value in printArr
• You may not use forEach or contentToString
• You must use a nested recursive function for your inner loop

Which version of printArr do you consider to be "better"? Why? (There is no correct answer.)

Functions that return functions

    fun main() {
        val pow4 = nthpower(4)
        println(pow4(2))
        println(pow4(3))
        println(pow4(4))
        println(pow4(5))
    
        println(nthpower(5)(2))
        println(nthpower(8)(2))
    }    

    16
    81
    256
    625
    32
    256  

• As always, no loops or vars
• You may not use forEach or any form of lists or arrays
• The returned function (and closure) must be recursive.

What is in the closure of the returned function?

Filtering

fun main() {
    val ll = listOf(1,2,3,4,5,6,7,8,9)
    println(ll.filter(isOdd) )
}
val isOdd = fun (n:Int) : Boolean {
    return (n%2!=0)
}

    fun main() {
        val ll = listOf(1,2,3,4,5,6,7,8,9)
        println(ll.filter(isOdd) )
    }
    val isOdd = { n:Int -> (n%2!=0) }    

    fun main() {
        val ll = listOf(1,2,3,4,5,6,7,8,9)
        println(ll.filter{ n:Int -> (n%2!=0) } )
    }    

    fun myFilter(funcc: (Int) -> Boolean, lst:List<Int>) : List<Int> {

1. a function that returns a boolean
2. a list of integers

Also, write at least 3 different filtering methods. One of these can be isOdd from above. The other two should be for your own creation.

You may add args with default values to your myFilter function if you find it convenient. Your implementation should not use the Kotlin filter function; it must use recursion. Your function may use MutableList and the add function of that class.

Once you have myFilter working, write a generic version with the following signature

    fun <Q> myFilterGeneric(funcc: (Q) -> Boolean, lst:List<Q>) : List<Q> {

For your generic filter, write at least two filtering methods, that work on two different data types. In your main function, include code showing each of these filters in use.

When you submit, submit both the generic and integer only versions of this function. For each you should have a main method that shows your function in operation.

What To Hand in

• Non tail recursive Hello world
• Tail recursive hello world
• Two versions of the program for printing 2-d arrays.
• Your nth power program
• Non-generic list filterer
• Generic list filterer
• Answers to the questions (in your readme). There are 4 questions.

Electronic Submissions

Your submission will be handed in using the submit script.

If you write your program on computers other than those in the lab, be aware that your program will be graded based on how it runs on the department’s Linux server, not how it runs on your computer. The most likely problem is not submitting everything or hard coding file locations that are not correct on the Linux servers.

Make a README

The easiest place to write your readme is within VSC. Make a file just like any other file but name it README.txt then just write in it. You should start by copying the sample readme.

Submit

If you developed this program on your own computer, you should be able to use the systems set up in lab to help get files to Linux. If you did not get SFTP set up within VSC then do the following:

1. Open a terminal window on your computer (a windows powershell or a Mac terminal)
2. Connect to a linux lab machine. A full list of possibly available lab machines is at Machine list. I will assume you are using goldengate.cs.brynmawr.edu -- you can use any machine. To connect:

                               ssh YOURNAME@goldengate.cs.brynmawr.edu
                                   or
                               ssh goldengate
                          

   Enter your Unix password if/when prompted
3. On the linux computer:

                                cd cs245
                                mkdir a3
                          

   You can change a3 to whatever you like, the directions below assume a1.
4. Leave this terminal window open and connected to Linux, you will use it again in a couple of steps
5. Within VSC open a terminal by going to the Terminal menu and selecting "new terminal"
6. In the Terminal inside of VSC you should be in the directory containing your program. Enter

                                scp * YOURNAME@goldengate.cs.brynmawr.edu:cs245/a3
                          

7. You should get messages on screen showing that each file in this directory has been copied. Make sure you get all of the files you want to submit.
8. Confirm that the copy was successful. Back in the Terminal you opened on the Linux machines (in the first steps)

                                ls a3
                          

   This should show a list of of the files copied in your scp command.
9. When all of the files are in the a1 directory and you are still in the cs245 directory

                                /home/gtowell/bin/submit  -c 245 -p 3 -d a3
                          

   This says to submit for project 3 (-p) everything in the directory a1 (-d) for the class 245 (-c). You should see listing of all the files you submitted and a message that says "success".
10. You can submit multiple times. I will grade only the last submission -- unless you tell me otherwise. The submission process attaches a timestamp so I know when you submitted (down to the second). The closest submission I have ever received to the deadline is 7 seconds.

The submission should include the following items:

README:

This file should follow the format of this sample README

Source files

All of them

Question answers

If separate from readme.

Data files used:

Be sure to include any non-standard data files uses. (Rare)

DO NOT INCLUDE:

Data files that are read from the class site. Do include any of your own data files.

Again: Once you have everything you want to submit in the a3 directory within /home/YOU/cs245/

1. Go to the directory /home/YOU/cs245
2. Enter /home/gtowell/bin/submit -c 245 -p 3 -d a3