I just finished this. It took me about 5 hours in all. A good way to spend a Sunday afternoon I suppose.

I have a good knowledge of Python and have worked with Ruby in the past on a little Rails project of my own. I had forgotten anything I knew though. Yesterday, I don't think I would've been able to write a foobaz in ruby without looking for help online. This proved to be a welcome refresher. It's also a great way to compare and contrast Python and Ruby. I really like Python's philosophy and maybe solving all these ruby koans has made me appreciate Python's simplicity and predictability a bit more.

I wouldn't recommend this to a beginner however. While I think I now have a pretty good idea of what the language can do, there were no whys or recommendations about all these features. Maybe it would be a good starting point for someone coming from a similar language (like Python), before moving on to a good Ruby book.

There are also functional koans. Same idea for some other languages.

http://github.com/relevance/functional-koans

Each of the following languages has its own branch: Clojure, FSharp, Haskell, and Scala.

Going through these would be useful for any Rubyist, not just those learning. I have been using Ruby for a while now and I didn't know there was a difference between string << 'foo' and string += 'foo' until now.

I learned that difference while doing some genetic programming. The difference is quite visible when you do it a few million times.

  def test_changing_hashes
    hash = { :one => "uno", :two => "dos" }
    hash[:one] = "eins"

    expected = { :one => "eins", :two => "dos" }
    assert_equal expected, hash

    # Bonus Question: Why was "expected" broken out into a variable
    # rather than used as a literal?
  end

Can anyone help with the bonus question? From searching Google, I read that the reason:

    assert_equal { :one => "eins", :two => "dos" }, hash

gives an error is that Ruby believes this to be a block. But then why doesn't it consider the hash to be a block below:

    expected = { :one => "eins", :two => "dos" }

?

Edit: thanks jashkenas for the explanation! Edit2: for anybody else trying these, I think the version in github is more up-to-date, with some corrections:

http://github.com/edgecase/ruby_koans

This is one of those gotchas with Ruby's syntax for blocks clashing with Ruby's syntax for hash literals. I'm not familiar with the details of precisely why Ruby's parser handles some cases, and not others, but I bet there's a special case for assignment -- you can't ever assign a block literal, so it has to be a hash...

Here are some of the variants:

    method({ ... })  # hash

    method { ... }   # block, even though a hash would be possible.

    method = { ... } # hash

    method a, b, :c => d  # implicit hash

    method a, b { ... } # SyntaxError

    method(a, b) { ... } # block

Only #2 in that list is really a problem, because there are situations where you'd legitimately like to use both.

This is one reason why I always use parens on my method calls. Some rubyists find it cluttering, yeah, but I think it makes reading code easier.

The other one to watch out for is precedence of {} vs do; end. Example:

  > x = [1,2].map do |i| i*2; end
   => [2, 4] 
  > puts [1,2].map do |i| i*2; end
  1
  2
   => nil
  > puts [1,2].map { |i| i*2}
  2
  4
   => nil

Agreed. It's why we've tried to be careful with lambda/hash/call syntax in CoffeeScript, especially where some of it is optional, and can be left out. For example:

    x = [1, 2].map (i) -> i * 2

... is without optional parens.

    x = [1, 2].map((i) -> i * 2)

... is with them.

    configure start: 10, end: 25

... is the syntax for calling a method and passing an implicit hash -- and with the optional braces and parens added, it's closer to JavaScript...

    configure({start: 10, end: 25})

#5 is also not a syntax error. Rather b is interpreted as a method and the block is associated with it.

There is also a python port available @ http://wiki.github.com/gregmalcolm/python_koans/

Already posted http://news.ycombinator.com/item?id=1622245

Periods. Not a cure for sentence fragments.

I used Koans when I first started out. Loved it. Still use it occasionally for reference.

Pretentious

Possibly, although I guess it's trying to play off Ruby's Japanese connotations and the actual examples inside (slicing arrays containing peanut butter and jelly) are not particularly pretentious.

Edit: thanks zem: http://en.wikipedia.org/wiki/Hacker_koan Edit2: and thanks angrycoder, I didn't spot that, although the point still stands that peanut butter is not overly pretentious

I think you are trying too hard. The most obvious influence is "The Little Schemer", right down to the peanut butter and jelly references. It is even listed as an inspiration on website.

not really, the koan has been enthusiastically adopted by the hacker community long before ruby came on the scene. i think this is more a continuation of that than any reference to ruby's japanese roots.