Project 4 warmup: Erlang exercises

Due: Tuesday, November 20, 1:59 PM

Updates

• 11/13, 9:20am, changed file name from lists.erl to mylists.erl. Clarified that the fibonacci and factorial functions should return integers.

Overview

These are a bunch of exercises to get your feet wet with Erlang programming. Among other things, doing these should help prepare you for the exam.

This project will be worth only 2% of your grade. To get full credit, you just have to turn something in that makes an attempt at every function. Note that for some of these, the answers are likely available somewhere on-line. I'm not going to check for cheating; if you don't make a serious attempt yourself to work out the problems, you will suffer on the exam which is worth a lot more of your grade. There will be no late deadline; you must turn it in on time to get credit.

You will almost certainly want to refer to the Erlang documentation. Links to tutorials, books, and manual pages are on the main course schedule page.

The Exercises

• Implement the following functions (in file mylists.erl):
  • rev(L) reverses list L
  • sum(L) sums the elements in the list L (an empty list is 0)
  • multwo(L) multiples every element of a list by 2
  • split(L) returns a pair of two lists {EL,OL} where EL is the list of even numbers in L and OL is the list of odd numbers. The ordering of the numbers should be the same as in the original list.
  • app(Fs,Xs) returns a list Ys where Fs is a list of n functions, and Xs is a list of n integers, and Ys is the list with the ith element of Fs applied to the ith element of Xs. So, for example,

     app([fun (X) -> X+1 end, fun (X) -> X-1 end], [1,5]).
    

    will produce list [2,4].
• Implement the factorial and fibonacci functions (returning N! for the first and the Nth fibonacci number for the second, where N is the input) in Erlang, using recursion. Make two versions of each: one that uses if expressions, and one that uses multiple function clauses (named fibif and fib, and factif and fact, respectively). Put these in the file intfuns.erl
• Do the three exercises here: Concurrent Programming Exercises. Do all three in a single file processes.erl, naming the three functions twoproc, nproc, and starproc, respectively.
• In the file join.erl, write a server in Erlang waits to receive two messages from clients. When it receives the second message, it sends the atom success back to each. Your server is started by the function start, which spawns a thread to run a function loop that does the message processing. Clients should run the function call which send the messages to the server and wait for the result.
• Reimplement pairserver.erl to use the server.erl behavior. (This is analogous to the reimplementation sequence2.erl of the implementation sequence1.erl.) Put your code in the file pairserver2.erl.

Testing Your Submission on Linuxlab

Erlang is installed on Linuxlab and you can run it from the command line using erl like we do in class. Alternatively, you can install Erlang on your own machine and test the programs there.

A Note About Running in Eclipse

There is an Eclipse plugin for Erlang, called Erlide. Unfortunately, as far as I can tell it only works for version R14, not R16, which is the most recent version. I have been unable to get it to work, but it might work for you. You can find detailed instructions about setting up Erlide, including integrating an Erlang runtime here.

Because Erlide only allows Eclipse "Run Configurations" with a single argument, you may need to run your code using the Console. Once you have successfully provided an Erlang backend, look for the Console tab at the bottom of the screen. You can interact with the Console just as with the "erl" command-line tool, running your code with a command such as semaphore:test().

What to Turn In

Every file you submit should have your name and UID. Each file should also have a no-argument function test in it that actually runs the code you've implemented. As such, I ought to be able to iterate through all of your files, compile them, and then run FILE:test() to see things work. Feel free to use helper functions in your tests that we have provided in sample code, or that you write yourself.

Submit your code on the Department's Submit Server. Contact the TA if you have any troubles submitting.

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