Remove [Courses] from lesson names/post subjects

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From laurel.fan@gmail.com  Tue Nov  8 04:41:12 2005
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Date: Mon, 7 Nov 2005 09:33:58 -0800
From: Laurel Fan <laurel.fan@gmail.com>
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Subject: [Courses] [Ruby] Ruby course, Announcement
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Here's the "official" announcement of the Ruby course!  Thanks for
everyone's patience, and I hope we can have some fun with this!=20
Please join the courses mailing list and subscribe to the ruby topic
to participate.  Lesson 0 will be sent out today, so if you subscribe
today and miss it, please check the archives.

Audience
--------

This course is designed for both people completely new to programming
and for experienced programmers who want to learn another language
(FWIW, Ruby was approximately my 8th language, and about the 5th that
I've actually used "for real").

Format
------

This will be a discussion group format course.  I'll schedule certain
chapters of the book to be discussed at specified times, and make a
set of questions and programming problems to start off the discussion,
but I won't provide the content (that comes from the book).  I'll make
a commitment to help make sure everyone's questions are answered, but
all participants should feel free to answer questions and start
discussions: the course will be even more fun if we all bring our
experience and expertise.

Material
--------

We'll only be covering Ruby the language in this course.  You'll know
the language well enough to explore advanced topics such as Rails,
other web stuff, GUI programming, etc.  I'll be going on a 3 week
vacation at the end of December, so that will be a perfect time for
someone else to step up and do a mini-course on a more specific topic
(if that's something that you're interested leading, please keep it in
mind!).

Book
----

The book we're using is 'Programming Ruby', by Dave Thomas et al.  The
2nd edition is preferred, and may be purchased at your online/offline
bookstore of choice, or from the authors at
http://pragmaticprogrammer.com/titles/ruby/index.html. If you do not
wish to purchase the book, the 1st edition is online (for free) at
http://www.rubycentral.com/book/.  The 1st edition is sufficient for
this course, if you supplement it with the most recent online
documentation.


Lesson Plan
-----------

Lessons are deliberately large and spaced far apart to allow for
flexibility around everyone's holiday plans.  The dates are when the
discussion questions and programming problems will be posted; don't
feel required to have the reading finished by then.  Also, don't feel
required to only discuss topics covered in the latest readings.

Nov 7: Lesson 0
    Downloading and Installing
    General References

Nov 14:  Lesson 1:
    1. Getting Started (Foreword/Preface/Roadmap in 1ed)
    2. Ruby.new
    3. Classes, Objects, and Variables

Nov 28: Lesson 2:
    4. Containers, Blocks, and Iterators
    5. Standard Types
    6. More About Methods

Dec 12: Lesson 3:
    7. Expressions
    8. Modules
    9. Exceptions, Catch, and Throw

Dec 19: Lesson 4:
    10. Basic Input and Output
    11. Threads and Processes
    12. Unit Testing
    13. When Trouble Strikes

--
Laurel Fan
http://dreadnought.gorgorg.org

From laurel.fan@gmail.com  Tue Nov  8 12:37:05 2005
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From: Laurel Fan <laurel.fan@gmail.com>
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Subject: [Courses] [Ruby] Lesson 0: Installing, References,
        and your first homework assignment
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=3D Lesson 0: Installing and Documentation References

=3D=3D Installing

=3D=3D=3D Linux

Any modern Linux distribution has ruby package(s).  It might even
already be installed.  (To check, try 'ruby --version' in a shell). If
you don't have it, install it with the appropriate package management
system.  The exact procedure will vary for your distribution.  To
start with, for yum-based systems, try::

# yum install ruby

and for apt-get based systems:

# apt-get install ruby

If you need more help, ask on the list.

In both Fedora and Debian, irb (interactive ruby, which has a better
interactive UI than the plain old ruby command) and ri (documentation
tool) are separate packages (called irb and ri).  You'll probably want
to install those as well.

=3D=3D=3D Windows

There's an installer for Windows here:

http://rubyinstaller.rubyforge.org/wiki/wiki.pl

=3D=3D=3D Mac OS X

Tiger (10.4) comes with Ruby installed.  For earlier versions, try
this page:

http://homepage.mac.com/discord/Ruby/

(I found it on a google search and haven't tried it, so if you do, let
us know how it goes.)

=3D=3D Documentation References

There are lots of places to find documentation for Ruby.  Sinc nearly
everything you'd search for is an actual word (including 'ruby'
itself, of course), it can be hard to google for.

If you have the 2nd edition of the book, the API reference that starts
in about the middle of the book is great.  With the 1st edition, some
of that will be out of date.

The canonical source for online documentation is:

http://ruby-doc.org/

If you have Firefox/Mozilla, there's a fancy sidebar for ruby-doc:

http://ruby-doc.org/docbar/

If you have the 'ri' commad, you can use that for
documentation for libraries that you have installed.  For example:

> ri File.new
-------------------------------------------------------------- File::new
     File.new(filename, mode=3D"r")            =3D> file
     File.new(filename [, mode [, perm]])    =3D> file
------------------------------------------------------------------------
     Opens the file named by _filename_ according to _mode_ (default is

[...]

Finally, here is another online ruby book featuring cartoon foxes:

http://www.poignantguide.net/ruby/

Other websites that may be useful include:

RubyForge: http://rubyforge.org
Ruby home page (in English): http://ruby-lang.org/en


=3D=3D Homework

Please 'turn in' your homework on the courses list, using the [Ruby]
subject tag, and with a subject that has something about 'lesson 0'
and 'homework'.  It's not due by a specific time, but I would
recommend starting before the next lesson is posted (Mon Nov 14).

First, introduce yourself.  Do you know any other programming
languages?  What do you like/not like about them?  Why are you
interested in Ruby?  What are some things you'd like to learn to do?

Second, find and run any ruby program.  It can be something you wrote,
something you downloaded (hint, look on RubyForge), an example you
copied out of a book, something a friend wrote for you, etc.

Finally, look at the code.  Find a section of about 5-20 lines of
code, and try to figure out what it does.  If you figure it out (or
just have a good guess), explain it to us.  If not, show us the code
and we'll try to explain it.

That's it, Lesson 1 (covering Chapters 1-3 of the book, "Getting
Started", "Ruby.new", and "Classes, Objects, and Variables") is next
week, Mon Nov 14.  See you on the list!

--
Laurel Fan
http://dreadnought.gorgorg.org

From Mallory.Chua@students.olin.edu  Tue Nov  8 14:51:12 2005
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Date: Mon, 07 Nov 2005 22:38:52 -0500
From: Mel Chua <mallory.chua@students.olin.edu>
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        homework assignment
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Hi, I'm Mel. This is my first class. I'm an electrical engineering 
student at Olin College in Boston, and don't know as much about coding 
as my friends seem to believe, but I'm trying to fix that. I was sort of 
the token "coder girl" in high school and tend more towards theory than 
hacking, and I'm also trying to tip that balance to the other side. I 
want to learn how to mess with things and not be afraid of blowing up my 
computer, darn it.

I've worked with C++, C, Python, and Scheme, but never got too in-depth 
with any of them, though I loved Python's 
"just-hack-it-together"-ability and the way Scheme makes you think 
differently than any other language I've seen. Ruby piqued my interest 
because I've heard it's a beautiful yet powerful little language, and 
wanted to learn more. I've been meaning to play with Ruby On Rails, so I 
figured this might be a good place to start before launching into that.

Homework the First - I tried looking at wiki.rb from the Instiki source 
code (a wiki written in Ruby - it's spiffy, and I'd like to learn how it 
works). Thankfully, it's well-commented and cleanly-written. I still 
have no idea what is going on, but here are my guesses.

This is code for something called a Word, which is a type of WikiLink. 
It's any group of letters that fits the wiki_word_pattern, whatever that 
is. If the code finds that the wiki word is escaped, it'll mark the 
entire inputted word as escaped; otherwise it marks nothing as escaped 
and cranks the entire thing through, hooking it up to a link of the same 
name. I can't tell you what individual lines of code do, though.

#---------- begin code ---------------
  # This chunk matches a WikiWord. WikiWords can be escaped
  # by prepending a '\'. When this is the case, the +escaped_text+
  # method will return the WikiWord instead of the usual +nil+.
  # The +page_name+ method returns the matched WikiWord.
  class Word < WikiLink

    attr_reader :escaped_text
   
    unless defined? WIKI_WORD
      WIKI_WORD = Regexp.new('(":)?(\\\\)?(' + 
WikiWords::WIKI_WORD_PATTERN + ')\b', 0, "utf-8")
    end

    def self.pattern
      WIKI_WORD
    end

    def initialize(match_data, content)
      super
      @textile_link_suffix, @escape, @page_name = match_data[1..3]
      if @escape
        @unmask_mode = :escape
        @escaped_text = @page_name
      else
        @escaped_text = nil
      end
      @link_text = WikiWords.separate(@page_name)
      @unmask_text = (@escaped_text || @content.page_link(@page_name, 
@link_text, @link_type))
    end

  end


From laurel.fan@gmail.com  Sat Nov 12 05:41:52 2005
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Date: Fri, 11 Nov 2005 10:41:45 -0800
From: Laurel Fan <laurel.fan@gmail.com>
To: Mel Chua <mallory.chua@students.olin.edu>
Subject: Re: [Courses] [Ruby] Lesson 0: Installing, References,
        and your first homework assignment
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On 11/7/05, Mel Chua <mallory.chua@students.olin.edu> wrote:
> Hi, I'm Mel.
[snip]

Hi Mel!

> Homework the First - I tried looking at wiki.rb from the Instiki source
> code (a wiki written in Ruby - it's spiffy, and I'd like to learn how it
> works). Thankfully, it's well-commented and cleanly-written. I still
> have no idea what is going on, but here are my guesses.
>
> This is code for something called a Word, which is a type of WikiLink.
> It's any group of letters that fits the wiki_word_pattern, whatever that
> is. If the code finds that the wiki word is escaped, it'll mark the
> entire inputted word as escaped; otherwise it marks nothing as escaped
> and cranks the entire thing through, hooking it up to a link of the same
> name. I can't tell you what individual lines of code do, though.

It is a little hard to figure out what just this but does, since it
looks like ot uses stuff from things elsewhere in the code.  But I'll
do my best to explain what each lines do:

> #---------- begin code ---------------
>   # This chunk matches a WikiWord. WikiWords can be escaped
>   # by prepending a '\'. When this is the case, the +escaped_text+
>   # method will return the WikiWord instead of the usual +nil+.
>   # The +page_name+ method returns the matched WikiWord.
>   class Word < WikiLink

Word inherits from WikiLink, which means that a Word can do everything
a WikiLink can, and maybe more.  Lesson 1 will talk a bit more about
this

>     attr_reader :escaped_text

This means that Word has an attribute called escaped_text, that you
can read, but not write.  So you could say something like
print word.escaped_text
to get the value of escaped_text, but you could not do
word.escaped_text =3D "something else"

>     unless defined? WIKI_WORD
>       WIKI_WORD =3D Regexp.new('(":)?(\\\\)?(' +
> WikiWords::WIKI_WORD_PATTERN + ')\b', 0, "utf-8")
>     end

All variables starting with a capital letter are constants (meaning
you can define them once, but never change them again).

>     def self.pattern
>       WIKI_WORD
>     end

Saying self. before a function name turns it into a class method,
instead of an instance method.  Which means you don't have to have an
instance of a WikiWord to call it.  Lesson 1 will also talk more about
class methods and instance methods.  (class methods are similar to
static methods in Java).

>     def initialize(match_data, content)

initialize is the magical method that gets called when you do new() on
an object.  So if you said:

Word.new(match_data, content)

it would call this method.

>       super

super calls the same method in the superclass (the class that we
inherit from), in this case it's WikiLink.

>       @textile_link_suffix, @escape, @page_name =3D match_data[1..3]

This sets the value of some instance methods to the second, third, and
fourth elements of the array match_data (we'll talk about arrays in
Lesson 2)

The below is a guess, since I'm not sure what all this stuff means
>       if @escape
>         @unmask_mode =3D :escape
>         @escaped_text =3D @page_name
>       else
>         @escaped_text =3D nil
>       end

if/else/end will be familar to anyone who's already done some
programming.  For those who haven't, they do exactly what they look
like: if @escape is true, do the two things after that, otherwise, do
the thing after else.

: before a variable turns it into a symbol.  It's actually a bit of a
tricky concept to understand, but most people just use them the same
way they would use constants (if I said :escape again elsewhere in the
program, it would have the same value and mean the same thing). It's
in the book, but we won't officially cover them.=20
http://www.rubycentral.com/faq/rubyfaq-6.html also talks about
symbols.

>       @link_text =3D WikiWords.separate(@page_name)

>       @unmask_text =3D (@escaped_text || @content.page_link(@page_name,
> @link_text, @link_type))

|| is or.  We're assigning something to @unmask_text here.  If
@escaped_text is something, then @unmask_text will be @escaped_text.=20
Otherwise, @unmask_text will be the @content.page_link(...) thing.=20
(observant readers will notice that this seems like it's doing the
same thing as the if/else/end we talked about above.  ruby is like
perl in that there is more than one way to do many things).

@content.page_link(... is calling a method called page_link on the
@content object (we'll talk about objects and methods in Lesson 0)

>     end
>   end

The end.  Instead of using braces or spacing like other languages, in
Ruby we use the word end to tell it when we're done with certain
things (like if, class, or def in this example).

--
Laurel Fan
http://dreadnought.gorgorg.org

From katie@hoteldetective.org  Wed Nov  9 09:45:50 2005
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From: Katie Bechtold <katie@hoteldetective.org>
To: courses@linuxchix.org
Subject: Re: [Courses] [Ruby] Lesson 0: Installing, References,
        and your first homework assignment
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> First, introduce yourself.  Do you know any other programming
> languages?  What do you like/not like about them?  Why are you
> interested in Ruby?  What are some things you'd like to learn to do?

Hi, I'm Katie!  Depending on the definition of "know", I know C,
C++, Java, Perl, Python, Fortran 77, Lisp, and Forth.  My favorites
among those are Python and Forth, both of which are flexible and
elegant, and both of which feature an interactive mode where you can
script "on the fly".  For me, the biggest sin of a programming
language is difficult readability, which is why I avoid Fortran like
the plague and haven't been able to appreciate Lisp as much as other
people.

I became interested in Ruby after reading Why's (Poignant) Guide to
Ruby[1] and hearing people rave about Ruby on Rails.  It looks like
Ruby's creator put a lot of thought into making life easier for
programmers.  I don't have any particular goals with respect to
Ruby; I'm just curious about it.

> Finally, look at the code.  Find a section of about 5-20 lines of
> code, and try to figure out what it does.

I found a Ruby application called rubyPod[2].  It's "a graphical
frontend for managing a iPod on Linux."  Here's a snippet from its
song.db:

class Song
  include Comparable

  ...

  def <=>(songb)
    if @pathSong==songb.pathSong
      0
    else
      #if the path is not the same then the songs cannot be equal
      if @nameArtist.downcase<songb.nameArtist.downcase
        -1
      elsif @nameArtist.downcase>songb.nameArtist.downcase
        1
      else
        if @nameAlbum.downcase<songb.nameAlbum.downcase
          -1
        elsif @nameAlbum.downcase>songb.nameAlbum.downcase
          1
        else
          @numSong.to_i<=>songb.numSong.to_i
        end
      end
    end
  end
end

What we have here is a method inside the Song class.  This method is
overloading Ruby's general comparison operator '<=>', which returns
-1, 0, or 1 depending on whether its left-hand operand is less then,
equal to, or greater than its right-hand operand.  Here, I think the
current Song object serves as the left-hand operand, and another
Song object denoted by 'songb' serves as the right-hand operand.

The first comparison in this function definition tests whether a
song is being compared to itself, to which it should be considered
equal.  The next test compares the lowercase version of the artist's
name (for case-insensitive sorting).  If those are equal, this
method compares the lowercase version of the album name.  If those
are also equal, it casts the songs' track numbers to integers and
compares them using the <=> operator for integers.


[1] http://poignantguide.net/ruby/
[2] http://rubypod.sourceforge.net/

-- 
Katie Bechtold         http://hoteldetective.org/



From laurel.fan@gmail.com  Mon Nov 14 11:38:58 2005
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        and your first homework assignment
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On 11/8/05, Katie Bechtold <katie@hoteldetective.org> wrote:
> Hi, I'm Katie!

> My favorites
> among those are Python and Forth, both of which are flexible and
> elegant, and both of which feature an interactive mode where you can
> script "on the fly".

You should definitely check out irb then, if you haven't already.

> I found a Ruby application called rubyPod[2].  It's "a graphical
> frontend for managing a iPod on Linux."  Here's a snippet from its
> song.db:
>
> class Song
>   include Comparable
>
>   ...
>
>   def <=3D>(songb)
>     if @pathSong=3D=3Dsongb.pathSong
>       0
>     else
>       #if the path is not the same then the songs cannot be equal
>       if @nameArtist.downcase<songb.nameArtist.downcase
>         -1
>       elsif @nameArtist.downcase>songb.nameArtist.downcase
>         1
>       else
>         if @nameAlbum.downcase<songb.nameAlbum.downcase
>           -1
>         elsif @nameAlbum.downcase>songb.nameAlbum.downcase
>           1
>         else
>           @numSong.to_i<=3D>songb.numSong.to_i
>         end
>       end
>     end
>   end
> end
>
> What we have here is a method inside the Song class.  This method is
> overloading Ruby's general comparison operator '<=3D>', which returns
> -1, 0, or 1 depending on whether its left-hand operand is less then,
> equal to, or greater than its right-hand operand.  Here, I think the
> current Song object serves as the left-hand operand, and another
> Song object denoted by 'songb' serves as the right-hand operand.
>
> The first comparison in this function definition tests whether a
> song is being compared to itself, to which it should be considered
> equal.  The next test compares the lowercase version of the artist's
> name (for case-insensitive sorting).  If those are equal, this
> method compares the lowercase version of the album name.  If those
> are also equal, it casts the songs' track numbers to integers and
> compares them using the <=3D> operator for integers.

Great explanation!

A few other interesting things about this code:  Comparable is a mixin
(for those experienced with other OO languages, mixins are kind of
like multiple inheritance but actually not at all like it).  Including
Comparable lets you get a whole bunch of comparison operators
(between?, =3D=3D, <, >=3D, etc.), simply by implementing the <=3D> functio=
n.=20
Here's some documentation on Comparable:

http://ruby-doc.org/core/classes/Comparable.html

Enumerable is another very useful mixin.  We'll learn more about those
in Lesson 3, in the Modules chapter of the book.

Another thing you may notice is that there are no 'return' statements
anywhere.  Like perl and matlab (and probably other languages), if
there is no explicit return statement, the return value of the method
is the last statement evaluated.  We'll learn about methods in Lesson
1 (and then more about them in Lesson 2).

--
Laurel Fan
http://dreadnought.gorgorg.org

From chantal@antenna.nl  Wed Nov  9 21:27:34 2005
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Hi I'm Chantal, I am a linux/freebsd/windows sysadmin at a small 
internet service provider. I am definitely not an experienced programmer 
but I like to write some bash scripts every now and then to make my life 
as a sysadmin easier and more fun, and I know some php. I'm interested 
in ruby because I want to learn a new programming language and a lot of 
people seem to be enthusiastic about it, I guess I am just curious. I 
want to learn a language in which I can write more sophisticated 
sysadmin tools in the future and I thought ruby might be a candidate (or 
perl but I can learn that some other time too). Well anyway, here's my 
homework, some code I wrote myself, I needed to configure an interface 
on an openbsd system for a whole ip range and it had to put something 
like this:

inet alias x.y.z.1 255.255.255.0
inet alias x.y.z.2 255.255.255.0

etc

I didn't want to type all of that so I wrote ipspitter.rb:
It basically takes a number to start with and adds one a number of times 
and keeps printing that, together with a string for the first three 
parts of the ip address and some text if you want

#!/usr/bin/ruby

puts "This is ipspitter"
puts "Which number do you want to start the range with?"

count = gets.to_i
sum = count

puts " How many ip addresses do you want?"

number = gets.to_i
number = number - 1
puts "Enter the first three parts of the ip-address (for example 
192.168.4. )"
range = gets.chomp

puts "Do you want to put some text in front of the ip-address? Put it here"
textbefore = gets.chomp

puts "Do you want to put some text after the ip-address? Put it here"
textafter = gets

puts textbefore + range + count.to_s + textafter

number.times do
       count +=1
       sum += count
       puts textbefore + range + count.to_s + textafter
end



From rachel@xtreme.com  Wed Nov  9 22:14:17 2005
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> First, introduce yourself.  Do you know any other programming
> languages?  What do you like/not like about them?  Why are you
> interested in Ruby?  What are some things you'd like to learn to do?

Hello All, and thanks Laurel for organizing this!

I've been programming in Java for about 5 years now, mostly webapps, 
meaning that I use html and javascript extensively as well.  I used to 
focus specifically on telephone apps, writing the UI in VoiceXML; but 
testing your app by calling it up on the phone sucks really hard!  I can 
get around in C# & ASP, and PHP, and get into trouble in Perl.  I have 
to say I like them all except PHP, which makes it far too easy to write 
bad code, and far too hard to write good code.  Good for beginners, though.

> 
> Second, find and run any ruby program.  It can be something you wrote,
> something you downloaded (hint, look on RubyForge), an example you
> copied out of a book, something a friend wrote for you, etc.
> 
> Finally, look at the code.  Find a section of about 5-20 lines of
> code, and try to figure out what it does.  If you figure it out (or
> just have a good guess), explain it to us.  If not, show us the code
> and we'll try to explain it.

I've got a very simple example, "cat" implemented in Ruby.  I more or 
less wrote it - I found parts from here & there and put them together. 
But I do understand what each line does, more or less, and it will run 
if you put it in a file by itself.  But remove the line numbers first, 
which I've added for reference!  Here goes:

----
  1  #! /usr/bin/ruby
  2
  3  fileName = ARGV[0] ? ARGV[0] : exit
  4
  5  begin
  6      IO.foreach(fileName) { | line |
  7          puts line
  8      }
  9  rescue
10      $stderr.puts $!
11  end
----

LINE 1: the shebang line (i assume it's still called that in Ruby!) 
Lets you run it without typing "ruby" first:

$ ./cat.rb filename.txt

of course, you can still run it through ruby:

$ ruby cat.rb filename.txt


LINE 3: Get the name of the file from the arguments list and assign it 
to the variable, fileName.  (This is a SIMPLE cat function that only 
looks at the first argument and ignores any others.)  If no argument is 
provided, just stop right there.  I used the ternary operator, see 
footnote [0] if you aren't familiar with it.


LINE 5: Starts a block of code.  I'm almost certain that begin/end (see 
line 11) are there as bookends to the rescue statement (line 9) to 
explicitly delimit a block of code that is likely to throw an exception. 
  If the rescue wasn't needed, the begin/end wouldn't be either.


LINE 6: This is the heart of cat.  IO is (I believe) a builtin Ruby 
object that handles file input & output.  Its foreach method takes a 
file name as argument, opens the file, and iterates through the lines in 
the file.

The bit with the pipe symbols after the open bracket is a mixin, and 
it's the thing I'm least familiar with here....  I think it defines the 
variable name for the object returned by the foreach method, for use 
within the scope of the code block that comes after it.  I think it is a 
little like the for each syntax, in Java 5:

List<Line> linesInFile = getLines();
for( Line line : linesInFile ) {
    // do stuff
}

but, obviously, shorter.  I do know that "line" isn't a Ruby reserved 
word here or anything, I tried "blarg" also and that worked just fine.

Anyone can talk more about this, please do!


LINE 7: puts is Ruby's print function.


LINE 8: ends the scope of the variable, line (or blarg)


LINE 9: rescue appears to be a Ruby catch statement.  IO stuff is always 
dangerous and error-prone and most languages offer some way of 
recovering from IO errors (no file, weird characters, permissions 
problems, and so forth).


LINE 10: what to do if there IS an error - print it out to standard 
error (which may or may not be the same place a plain puts writes to).


LINE 11: remember the begin statement in line 5?  we're done with that 
block now.


That's all, then.  I have to say that an in-depth analysis like that 
helped ME a ton even for such a short little scrap of code.  NEXT!

Rachel



[0] The ternary operator is like a shortened IF/ELSE statement.  It 
looks like this:

TEST ? TRUE_RESULT : FALSE_RESULT

As an IF statement, it would look like this:

if( TEST ) {
   TRUE_RESULT;
} else {
   FALSE_RESULT;
}

It's called "ternary" because it has three arguments; it's the only 
operator that takes more than two.

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Laurel Fan wrote:

> First, introduce yourself. Do you know any other programming
>
>languages?  What do you like/not like about them?  Why are you
>interested in Ruby?  What are some things you'd like to learn to do?
>  
>

G'day,

I intend to do this course, but as I am preparing for an exam next week 
I won't actually start until after then. Still I thought that I would 
give a short introduction.

I know a lot of other languages, and I suppose that you could say that 
learning new languages is a a bit of a hobby of mine. (Other people 
collect stamps).  My biggest problem is that I don't know any language 
really well.  What I like is languages that have different ways of 
thinking about them, e.g. Prolog is very different to C which is also 
very different to Java despite the similarities.  What I don't like is 
VB which seems to be a mismash of different languages, and constantly 
changing to try and copy the latest popular language.

Ruby seems to have a different way of thinking associated with it, being 
for one thing a totally Object oriented language, so that is the first 
thing that got my interest.  Also speed of development seems to be part 
of Ruby, and the promise of using Ruby on rails to develop a web 
application painlessly seems worth investigating.

I do have some applications where I may use Ruby if it seems 
appropriate, but I need to know more about it before I can make any 
decision like that!

sue





From beth-lists@compu-diva.com  Thu Nov 10 04:28:29 2005
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Hi all -
I'm not going to get to this for a week either, so I'll just introduce
myself.  My name is Beth Camero, I'm a 49 y.o. semi-geeky woman,
managing network/desktop/web support for a mid-size non-profit
association in Sacramento, California.  I've worked there for 15 years,
and basically created the job I have.  I was hired lo those 15 years ago
as a non-typing secretary who had never touched a computer.  Somebody
there showed me WordPerfect on a little old PC (one of 3 stand-alones,
tennis-shoe network only) and I fell in love.  Learned lots, became the
computer guru for the office, grew a network and turned us into a
[fairly] high-tech place.

I'm probably in the wrong place.  I've never done any real programming
but I'm interested in it.  I have programmers who come in and work for
me occasionally and we do web projects together.  I don't remember where
I ran across Ruby but it sounded so interesting that I thought I'd see
if I could do it.  Worth a shot! I don't know anyone who is using it,
but quickly creating web apps - what a concept! There are SO many things
I'd like to do at work but don't have the $$ for the programming ...
I'm going to be working on a Windoze system, I hope that won't be a
problem.  I have a couple of Linux servers at work, but I don't have any
Linux desktops.
My kid is going to take this course, too - he's  a newbie
programmer/techie but smart as a whip.  I'm hoping he'll  be able to
help me. :)
Wish me luck!
Beth


Laurel Fan wrote:
> = Lesson 0: Installing and Documentation References
>
> == Installing
>
> === Linux
>
> Any modern Linux distribution has ruby package(s).  It might even
> already be installed.  (To check, try 'ruby --version' in a shell). If
> you don't have it, install it with the appropriate package management
> system.  The exact procedure will vary for your distribution.  To
> start with, for yum-based systems, try::
>
> # yum install ruby
>
> and for apt-get based systems:
>
> # apt-get install ruby
>
> If you need more help, ask on the list.
>
> In both Fedora and Debian, irb (interactive ruby, which has a better
> interactive UI than the plain old ruby command) and ri (documentation
> tool) are separate packages (called irb and ri).  You'll probably want
> to install those as well.
>
> === Windows
>
> There's an installer for Windows here:
>
> http://rubyinstaller.rubyforge.org/wiki/wiki.pl
>
> === Mac OS X
>
> Tiger (10.4) comes with Ruby installed.  For earlier versions, try
> this page:
>
> http://homepage.mac.com/discord/Ruby/
>
> (I found it on a google search and haven't tried it, so if you do, let
> us know how it goes.)
>
> == Documentation References
>
> There are lots of places to find documentation for Ruby.  Sinc nearly
> everything you'd search for is an actual word (including 'ruby'
> itself, of course), it can be hard to google for.
>
> If you have the 2nd edition of the book, the API reference that starts
> in about the middle of the book is great.  With the 1st edition, some
> of that will be out of date.
>
> The canonical source for online documentation is:
>
> http://ruby-doc.org/
>
> If you have Firefox/Mozilla, there's a fancy sidebar for ruby-doc:
>
> http://ruby-doc.org/docbar/
>
> If you have the 'ri' commad, you can use that for
> documentation for libraries that you have installed.  For example:
>
>   
>> ri File.new
>>     
> -------------------------------------------------------------- File::new
>      File.new(filename, mode="r")            => file
>      File.new(filename [, mode [, perm]])    => file
> ------------------------------------------------------------------------
>      Opens the file named by _filename_ according to _mode_ (default is
>
> [...]
>
> Finally, here is another online ruby book featuring cartoon foxes:
>
> http://www.poignantguide.net/ruby/
>
> Other websites that may be useful include:
>
> RubyForge: http://rubyforge.org
> Ruby home page (in English): http://ruby-lang.org/en
>
>
> == Homework
>
> Please 'turn in' your homework on the courses list, using the [Ruby]
> subject tag, and with a subject that has something about 'lesson 0'
> and 'homework'.  It's not due by a specific time, but I would
> recommend starting before the next lesson is posted (Mon Nov 14).
>
> First, introduce yourself.  Do you know any other programming
> languages?  What do you like/not like about them?  Why are you
> interested in Ruby?  What are some things you'd like to learn to do?
>
> Second, find and run any ruby program.  It can be something you wrote,
> something you downloaded (hint, look on RubyForge), an example you
> copied out of a book, something a friend wrote for you, etc.
>
> Finally, look at the code.  Find a section of about 5-20 lines of
> code, and try to figure out what it does.  If you figure it out (or
> just have a good guess), explain it to us.  If not, show us the code
> and we'll try to explain it.
>
> That's it, Lesson 1 (covering Chapters 1-3 of the book, "Getting
> Started", "Ruby.new", and "Classes, Objects, and Variables") is next
> week, Mon Nov 14.  See you on the list!
>
> --
> Laurel Fan
> http://dreadnought.gorgorg.org
> _______________________________________________
> Courses mailing list
> Courses@linuxchix.org
> http://mailman.linuxchix.org/mailman/listinfo/courses
>
>   



From joseph.hall@gmail.com  Thu Nov 10 06:47:49 2005
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Hello,

My name is Joseph Hall. I've used C++ and Java the most "for real" (at
work), but in college I TA'ed Programming Languages and we went over Java,
Scheme, and Miranda. I also was forced to learn and use Perl at work but I
don't like it. The last couple of weeks at work I've been using a language
called LUA, which is lightweight, fast, stack-based, and the interpreter is
easily embedded in C/C++ apps. Right now I know very little about Ruby. I
want to learn Ruby for fun, not necessarily because I think I'll use it. I
am also interested in participating because I am Laurel's b.f.

I found some simple Ruby on the internet and tweaked it.

---
#!/usr/bin/ruby

def fib(n)
a =3D 0
b =3D 1
n.times do
a, b =3D b, a+b
end
a
end

N =3D Integer(ARGV.shift || 1)
print "Fib(", N, ") is ", fib(N), "\n"
---


This is computing Fibonacci numbers. I guess the ARGV line is getting
command line parameters, and defaulting to "1" if none are given. Pretty
readable yet compact. Why does N need an explicit Integer()
cast/type/whatever but a and b don't? In Perl I wouldn't need that...

Since I know Scheme, I wanted to compare. I wrote this Scheme to do the sam=
e
thing:

---
(define (fib n)
(fib-helper n 1 1))

(define (fib-helper n a b)
(if (<=3D n 1)
a
(fib-helper (- n 1) b (+ a b))))

(fib 150000)
---

Even though this is a really simple algorithm, you need a helper function i=
n
Scheme in order to really get it right. The "a, b =3D" syntax in Ruby is
pretty cool.

I would expect the runtime of each to be comparable, but for large N the
Ruby is much faster than Scheme. I know nothing, but I'm venturing a guess
that Ruby is somehow compiled, whereas the Scheme is completely
interpreted...?

Joe

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Subject: Re: [Courses] [Ruby] Lesson 0: Installing, References,
        and your first homework assignment
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On 11/9/05, Joseph Hall <joseph.hall@gmail.com> wrote:
> Hello,

Hi!

> I found some simple Ruby on the internet and tweaked it.
>
> ---
> #!/usr/bin/ruby
>
> def fib(n)
> a =3D 0
> b =3D 1
> n.times do
> a, b =3D b, a+b
> end
> a
> end
>
> N =3D Integer(ARGV.shift || 1)
> print "Fib(", N, ") is ", fib(N), "\n"
> ---
>
>
> This is computing Fibonacci numbers. I guess the ARGV line is getting
> command line parameters, and defaulting to "1" if none are given

Yep.  ARGV is a list containing all of the command line parameters
(not including the filename of the program itself, which will be
different for C programmers.  That's in $0).

> Why does N need an explicit Integer()
> cast/type/whatever but a and b don't?
> In Perl I wouldn't need that...

This is because Ruby is strongly typed but Perl isn't.  Ruby is also
dynamically typed (and it has "duck typing" which I haven't seen in
any other mainstream language), which is why  you didn't have to say
anything like:

int a =3D 0

You assigned it to a Fixnum, so a is a Fixnum.

However, for N, the result of ARGV.shift is a String, so it needs to
be turned into an integer.

> I would expect the runtime of each to be comparable, but for large N the
> Ruby is much faster than Scheme. I know nothing, but I'm venturing a gues=
s
> that Ruby is somehow compiled, whereas the Scheme is completely
> interpreted...?

No, ruby is completely interpreted.  I think there are ways of
compiling it, at least into bytecode, but those are fairly obscure.=20
Maybe it's just because the scheme is recursive and the perl is not?=20
I don't know Scheme that well (my obligatory college class functional
language was ML), but does it look like the Scheme interpreter should
be doing a tail call optimization?

--
Laurel Fan
http://dreadnought.gorgorg.org

From qirien@icecavern.net  Sat Nov 12 05:00:08 2005
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From: Andrea Landaker <qirien@icecavern.net>
To: courses@linuxchix.org
Subject: Re: [Courses] [Ruby] Lesson 0: Installing, References,
        and your first homework assignment
Date: Fri, 11 Nov 2005 10:54:23 -0700
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I'm a computer programmer turned stay-at-home-mom, who still loves 
computers.  :-)  Most of my programming these days is simple Ruby scripts for 
myself or for my website (an audio/image gallery program, recoding mp3s, 
etc).  In the past I've used Java, C++, and Scheme, but I'm a big fan of 
Ruby.  I have never really sat down and "learned" it, though -- just started 
ploughing through getting things to work.  So I'm looking forward to learning 
some (probably basic) new things that I hadn't thought I needed but will 
probably be useful.

Not sure if I'll make it through the whole course due to the fact that my 
1-year-old hates me being on the computer (he likes to turn it off), but 
it'll be fun!

OK, for the next part of the homework, here's my husband's interactive 
crytpogram solver:

#!/usr/bin/ruby

$code = ARGV.join(' ').upcase

puts $code
print '$ '
STDOUT.flush
while STDIN.gets
  if ~ /([A-Za-z]{2}).*/
    code = $1[0..0].upcase
    text = $1[1..1].upcase
    $code.gsub!(code,'!')
    $code.gsub!(text,code)
    $code.gsub!('!',text)
  else
    puts "Enter xY to make x -> Y"
  end
  puts $code
  print '$ '
  STDOUT.flush
end

The first line puts all the "arguments" (the cryptogram itself) into the 
global variable "code", uppercased.  It prints it out, and then takes two 
letters from the user.  The first letter goes in the local variable "code", 
and the second goes into "text".  Then, throughout the global variable 
"code", it swaps the two (using the exclamation point for an intermediary 
character).  This repeats essentially forever.

-- 
Andrea Landaker
http://www.icecavern.net/~qirien/

From laurel.fan@gmail.com  Thu Nov 17 03:47:31 2005
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From: Laurel Fan <laurel.fan@gmail.com>
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        and your first homework assignment
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On 11/11/05, Andrea Landaker <qirien@icecavern.net> wrote:
>
Hi Andrea!

> OK, for the next part of the homework, here's my husband's interactive
> crytpogram solver:

Looks good!  Great example of using regular expressions and the gsub
function, which Perl programmes may be interested in..

> #!/usr/bin/ruby
>
> $code =3D ARGV.join(' ').upcase
>
> puts $code
> print '$ '
> STDOUT.flush
> while STDIN.gets
>   if ~ /([A-Za-z]{2}).*/
>     code =3D $1[0..0].upcase
>     text =3D $1[1..1].upcase

This [0..0] stuff is necessary because $1[0] would return a character
(which is actually a number, not a String).  Telling it [0..0] gives
it a range (here, it's the range from 0 to 0, the first character to
the first character), which makes it return a String.

>     $code.gsub!(code,'!')

gsub is "global substitution" (see String documentation for more).=20
What the exclamation mark does is do the gsub on $code itself (rather
than returning the result of doing gsub).  It's the same thing as:

$code =3D $code.gsub(code, '!')

One style note:  I would avoid using very similar variable names like
$code/code.  On the first read through I wasn't mentally pronouncing
the $, so I was very confused about what was going on.  The $ actually
means global variable, which in this case doesn't do much because you
have only one function anyway.  It's usually preferable to avoid
global variables for longer or more complicated programs.  However,
one benefit of Ruby is that if you're doing something simple enough
(like this) that OO and encapsulation won't help you, it won't get in
your way.  But using $ makes it look like Perl and we don't want that
;)

>     $code.gsub!(text,code)
>     $code.gsub!('!',text)
>   else
>     puts "Enter xY to make x -> Y"
>   end
>   puts $code
>   print '$ '
>   STDOUT.flush
> end
>
> The first line puts all the "arguments" (the cryptogram itself) into the
> global variable "code", uppercased.  It prints it out, and then takes two
> letters from the user.  The first letter goes in the local variable "code=
",
> and the second goes into "text".  Then, throughout the global variable
> "code", it swaps the two (using the exclamation point for an intermediary
> character).  This repeats essentially forever.

--
Laurel Fan
http://dreadnought.gorgorg.org

From laurel.fan@gmail.com  Thu Nov 17 09:46:17 2005
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        and your first homework assignment
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On 11/9/05, Beth Camero <beth-lists@compu-diva.com> wrote:
> Hi all -

Hi!

> I'm probably in the wrong place.  I've never done any real programming
> but I'm interested in it.

Well, this sounds like a great place for you to me, personally, but
I'm biased.  I hope you and your son enjoy the course!

--
Laurel Fan
http://dreadnought.gorgorg.org

From akkana@shallowsky.com  Thu Nov 10 07:12:27 2005
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From: Akkana Peck <akkana@shallowsky.com>
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Subject: Re: [Courses] [Ruby] Lesson 0: Installing, References,
        and your first homework assignment
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Hi! Laurel, thanks for running the course.

I'm a longtime programmer in lots of languages. My two favorites
are C and Python; I suppose because they're simple, compact and
efficient. I've used Ruby and Rails a little bit, but I want to
learn more about Ruby because although I can get by in it, I
don't feel like I understand it as well as I'd like to.

I expect most of my Ruby use will be for Rails, but who knows?
Maybe the course will convince me that I should use it instead of
Python for writing standalone scripts. And every language has
strengths and weaknesses, so even if I don't switch to Ruby as
my main scripting language, I'm sure there will be times when it's
the best tool for the job.

Laurel Fan writes:
> Any modern Linux distribution has ruby package(s).  It might even
> already be installed.  (To check, try 'ruby --version' in a shell). If

I'm currently running Ubuntu "Hoary Hedgehog". Although it offers
Ruby packages (which are probably fine for this course), I didn't
have much luck getting Rails and Gems to work, even after adding the
backports from Breezy. Also, the built-in Ruby didn't install a
"ruby" command so I had to make a symlink (I notice someone else
just asked about that on newchix recently).

I ended up building Ruby and Gems from source, then using gems to
install Rails. That worked fine and I've had no problem with the
setup. I suspect this all works out of the box on Breezy.

For my homework assignment, I rewrote in Ruby a little program that
I wrote last week for spam filtering. I suddenly started getting a
lot more spam with unprintable characters in the subject, so I
wanted a program to calculate how many characters in a set of
strings was printable vs. unprintable. I tried at first to write it
in Python, but it turned out Python doesn't have any easy way to do
the equivalent of C's "isprint" test. Eventually I gave up and wrote
it in C, which was really easy.

Googling, it turns out Ruby doesn't have a way to do isprint()
either. :-( But I did find a way to delete all unprintable characters
from a string, so I wrote it using that. (I think Python has that too,
so I could probably go back and write it in Python the same way.)

#!/usr/local/bin/ruby

# This program checks its runtime arguments for number of
# printable and unprintable characters.

class SmartString < String
  def print_unprint()
    toprint = self.gsub(/[^[:print:]]/, '')
    return [toprint.length, self.length - toprint.length]
  end
end

# main: loop over each input word

total_printable = 0
total_unprintable = 0
ARGV.each do |word|
  p_u = SmartString.new(word).print_unprint()
  total_printable += p_u[0]
  total_unprintable += p_u[1]
end

print "Total: ", total_printable, " printable, ",
      total_unprintable, " unprintable\n"

You said to analyze part of the code, so I'll analyze the class
SmartString. I made it a new class that inherits from the normal
String class, so that I could use all the built-in string methods.
Eventually I'd probably want to add some other tests (e.g. checking
how much punctuation and numbers there is compared to letters, maybe
checking word length) but right now the only new method is a
function called print_unprint that returns an array of two items:
the number of printable characters in the string, and the number of
unprintable characters.

It does that by replacing (using gsub, which does a global
substitution over the string) any unprintable character in the string
with '' (i.e. deleting it). It turns out Ruby has a character class
called [:print:] (the character classes are listed on p. 72 of the
second edition of Programming Ruby) so [^[:print:]] matches any
character that's not printable. (I found that snippet by googling.
There are lots of useful Ruby snippets on the web if you google for
terms related to what you're trying to do.)

I confess I'm not 100% clear on the two sets of brackets: the outside
set says "for this regular expression, use any character in this
group" and I grok that, but the inner set with the colons, [::],
seems to be something you always put around character classes
but I'm not comfortable enough yet with the syntax to be sure why.

The return in print_unprint uses [ ] to build up a two-element array
on the fly, so it can return both the printable and unprintable counts.
Then the caller can index the printable count with [0] and the
unprintable count with [1]. If I were actually using this for a
spam filter, instead of printing the count I'd exit with a nonzero
status if there were too many unprintables.

        ...Akkana

From laurel.fan@gmail.com  Thu Nov 17 10:34:56 2005
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        and your first homework assignment
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On 11/9/05, Akkana Peck <akkana@shallowsky.com> wrote:
> Hi!

Hi Akkana!

> For my homework assignment, I rewrote in Ruby a little program that
> I wrote last week for spam filtering. I suddenly started getting a
> lot more spam with unprintable characters in the subject, so I
> wanted a program to calculate how many characters in a set of
> strings was printable vs. unprintable. I tried at first to write it
> in Python, but it turned out Python doesn't have any easy way to do
> the equivalent of C's "isprint" test. Eventually I gave up and wrote
> it in C, which was really easy.
>
> Googling, it turns out Ruby doesn't have a way to do isprint()
> either. :-( But I did find a way to delete all unprintable characters
> from a string, so I wrote it using that. (I think Python has that too,
> so I could probably go back and write it in Python the same way.)
>
> #!/usr/local/bin/ruby
>
> # This program checks its runtime arguments for number of
> # printable and unprintable characters.
>
> class SmartString < String
>   def print_unprint()
>     toprint =3D self.gsub(/[^[:print:]]/, '')
>     return [toprint.length, self.length - toprint.length]
>   end
> end
>
> # main: loop over each input word
>
> total_printable =3D 0
> total_unprintable =3D 0
> ARGV.each do |word|
>   p_u =3D SmartString.new(word).print_unprint()
>   total_printable +=3D p_u[0]
>   total_unprintable +=3D p_u[1]
> end
>
> print "Total: ", total_printable, " printable, ",
>       total_unprintable, " unprintable\n"
>
> You said to analyze part of the code, so I'll analyze the class
> SmartString. I made it a new class that inherits from the normal
> String class, so that I could use all the built-in string methods.
> Eventually I'd probably want to add some other tests (e.g. checking
> how much punctuation and numbers there is compared to letters, maybe
> checking word length) but right now the only new method is a
> function called print_unprint that returns an array of two items:
> the number of printable characters in the string, and the number of
> unprintable characters.

You could have done this by extending the String class itself (in the
context of your program only, of course).  We'll learn how later.

> It does that by replacing (using gsub, which does a global
> substitution over the string) any unprintable character in the string
> with '' (i.e. deleting it). It turns out Ruby has a character class
> called [:print:] (the character classes are listed on p. 72 of the
> second edition of Programming Ruby) so [^[:print:]] matches any
> character that's not printable. (I found that snippet by googling.
> There are lots of useful Ruby snippets on the web if you google for
> terms related to what you're trying to do.)

The character classes supported by Ruby are actually standard POSIX
character sets, and I think they work in othe rplaces like Perl,
Python, Java, etc...

> I confess I'm not 100% clear on the two sets of brackets: the outside
> set says "for this regular expression, use any character in this
> group" and I grok that, but the inner set with the colons, [::],
> seems to be something you always put around character classes
> but I'm not comfortable enough yet with the syntax to be sure why.

It's just what the regular expression thing does.  It's a way of
making the difference between "the character class isprint" and "match
the characters i, s, p, r..." really obvious.  I don't know of any
reason they chose that exact syntax, but I'm not a regex expert.  The
character classes are pretty standard.

> The return in print_unprint uses [ ] to build up a two-element array
> on the fly, so it can return both the printable and unprintable counts.
> Then the caller can index the printable count with [0] and the
> unprintable count with [1]. If I were actually using this for a
> spam filter, instead of printing the count I'd exit with a nonzero
> status if there were too many unprintables.

Looks good, and good analysis!  In the more-than-one-way department,
you could have used the String.scan function, documented here:
http://www.ruby-doc.org/core/classes/String.html#M001414

You would want something like:
input.scan(/[[:isprint:]]/).length

scan returns an array of matches, so to count the matches we're
calling length on the array it returns.

String.count also does something close to what you want (but it
wouldn't work here because it can't take a regular expression).  See
http://www.ruby-doc.org/core/classes/String.html#M001414

One of the philosophies of Ruby is that things should be made easy by
making library functions for common tasks (even if it would have taken
only 3 lines to do it the "normal" way).  There are lots of useful
little functions like this scattered around the builtin classes.

--
Laurel Fan
http://dreadnought.gorgorg.org

From kproot@nerim.net  Thu Nov 10 09:11:08 2005
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Date: Wed, 9 Nov 2005 23:12:35 +0100
From: Karine Delvare <kproot@nerim.net>
To: courses@linuxchix.org
Subject: Re: [Courses] [Ruby] Lesson 0: Installing, References, and your
        first homework assignment
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Hello! I'm Karine Delvare, french, 27 years old, working as a software
engineer mainly on web application. I have learned and used several
programming languages during my studies and at my jobplaces: C, C++,
C#, a bit of Java, a lot of PHP, Perl. I like object-oriented programming very much, but learned to pay attention to lightness. Now I mostly use PHP at work and C (with GObject) at home, and I remember with a smile the huge slow apps I wrote when .NET was "in"...

I am interested in Ruby out of curiosity. Many times I've been proven
wrong on what I thought was carved in stone about programming languages
and their mechanics, so I would like to have a look at as many as
possible to be able to compare. There is no special task I would like
to do with it, I'll just follow the assignments and maybe I'll come up
with something later on.

I played with tictactoe.rb, found on RubyForge. Here is a sample of
code:

# P1 Turn
        puts "Player 1's turn"
        puts "Select your space, enter the number that is in the space
you want" disp_board(numspac)
        space = gets.to_i # Get the space they want!

        while barr[space] != " "
                puts "Try again that one is taken!!!"
                disp_board(numspac)
                space = gets.to_i
        end
        barr[space] = "X"
# End of Turn
disp_board(barr)
check3row(barr)
# P2 Turn
[...]

Simple code with some input/output: asks the player where he wants to
play, check whether the space is free, display the updated board, check
if someone won. I don't understand the details of each line yet, but
Ruby seems like pretty east to read.

Karine.

From rsvidal@terra.com.br  Sat Nov 12 12:58:38 2005
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Hi!

I just deleted the Joe's mail, but I would like to know what means the co=
mmand "a,b=3D"

I will introduce myself soon, because I didnt my homework yet.

Thanks,

Renata
De:courses-bounces@linuxchix.org

Para:courses@linuxchix.org

C=F3pia:

Data:Wed, 9 Nov 2005 12:12:21 -0800

Assunto:Re: [Courses] [Ruby] Lesson 0: Installing, References, and your f=
irst homework assignment

> Hi! Laurel, thanks for running the course.
> 
> I'm a longtime programmer in lots of languages. My two favorites
> are C and Python; I suppose because they're simple, compact and
> efficient. I've used Ruby and Rails a little bit, but I want to
> learn more about Ruby because although I can get by in it, I
> don't feel like I understand it as well as I'd like to.
> 
> I expect most of my Ruby use will be for Rails, but who knows?
> Maybe the course will convince me that I should use it instead of
> Python for writing standalone scripts. And every language has
> strengths and weaknesses, so even if I don't switch to Ruby as
> my main scripting language, I'm sure there will be times when it's
> the best tool for the job.
> 
> Laurel Fan writes:
> > Any modern Linux distribution has ruby package(s). It might even
> > already be installed. (To check, try 'ruby --version' in a shell). If=

> 
> I'm currently running Ubuntu "Hoary Hedgehog". Although it offers
> Ruby packages (which are probably fine for this course), I didn't
> have much luck getting Rails and Gems to work, even after adding the
> backports from Breezy. Also, the built-in Ruby didn't install a
> "ruby" command so I had to make a symlink (I notice someone else
> just asked about that on newchix recently).
> 
> I ended up building Ruby and Gems from source, then using gems to
> install Rails. That worked fine and I've had no problem with the
> setup. I suspect this all works out of the box on Breezy.
> 
> For my homework assignment, I rewrote in Ruby a little program that
> I wrote last week for spam filtering. I suddenly started getting a
> lot more spam with unprintable characters in the subject, so I
> wanted a program to calculate how many characters in a set of
> strings was printable vs. unprintable. I tried at first to write it
> in Python, but it turned out Python doesn't have any easy way to do
> the equivalent of C's "isprint" test. Eventually I gave up and wrote
> it in C, which was really easy.
> 
> Googling, it turns out Ruby doesn't have a way to do isprint()
> either. :-( But I did find a way to delete all unprintable characters
> from a string, so I wrote it using that. (I think Python has that too,
> so I could probably go back and write it in Python the same way.)
> 
> #!/usr/local/bin/ruby
> 
> # This program checks its runtime arguments for number of
> # printable and unprintable characters.
> 
> class SmartString < String
> def print_unprint()
> toprint =3D self.gsub(/[^[:print:]]/, '')
> return [toprint.length, self.length - toprint.length]
> end
> end
> 
> # main: loop over each input word
> 
> total_printable =3D 0
> total_unprintable =3D 0
> ARGV.each do |word|
> p_u =3D SmartString.new(word).print_unprint()
> total_printable +=3D p_u[0]
> total_unprintable +=3D p_u[1]
> end
> 
> print "Total: ", total_printable, " printable, ",
> total_unprintable, " unprintable\n"
> 
> You said to analyze part of the code, so I'll analyze the class
> SmartString. I made it a new class that inherits from the normal
> String class, so that I could use all the built-in string methods.
> Eventually I'd probably want to add some other tests (e.g. checking
> how much punctuation and numbers there is compared to letters, maybe
> checking word length) but right now the only new method is a
> function called print_unprint that returns an array of two items:
> the number of printable characters in the string, and the number of
> unprintable characters.
> 
> It does that by replacing (using gsub, which does a global
> substitution over the string) any unprintable character in the string
> with '' (i.e. deleting it). It turns out Ruby has a character class
> called [:print:] (the character classes are listed on p. 72 of the
> second edition of Programming Ruby) so [^[:print:]] matches any
> character that's not printable. (I found that snippet by googling.
> There are lots of useful Ruby snippets on the web if you google for
> terms related to what you're trying to do.)
> 
> I confess I'm not 100% clear on the two sets of brackets: the outside
> set says "for this regular expression, use any character in this
> group" and I grok that, but the inner set with the colons, [::],
> seems to be something you always put around character classes
> but I'm not comfortable enough yet with the syntax to be sure why.
> 
> The return in print_unprint uses [ ] to build up a two-element array
> on the fly, so it can return both the printable and unprintable counts.=

> Then the caller can index the printable count with [0] and the
> unprintable count with [1]. If I were actually using this for a
> spam filter, instead of printing the count I'd exit with a nonzero
> status if there were too many unprintables.
> 
> ...Akkana
> _______________________________________________
> Courses mailing list
> Courses@linuxchix.org
> http://mailman.linuxchix.org/mailman/listinfo/courses

From laurel.fan@gmail.com  Thu Nov 17 02:21:10 2005
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From: Laurel Fan <laurel.fan@gmail.com>
To: courses@linuxchix.org
Subject: Re: [Courses] [Ruby] Lesson 0: Installing, References,
        and your first homework assignment
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reply to chantal

On 11/9/05, Chantal Rosmuller <chantal@antenna.nl> wrote:
> Hi I'm Chantal

Hi!

> Well anyway, here's my
> homework, some code I wrote myself, I needed to configure an interface
> on an openbsd system for a whole ip range and it had to put something
> like this:
>
> inet alias x.y.z.1 255.255.255.0
> inet alias x.y.z.2 255.255.255.0
>
> etc
>
> I didn't want to type all of that so I wrote ipspitter.rb:
> It basically takes a number to start with and adds one a number of times
> and keeps printing that, together with a string for the first three
> parts of the ip address and some text if you want

This looks great, a few comments (for you and everyone else) in-line:

> #!/usr/bin/ruby
>
> puts "This is ipspitter"
> puts "Which number do you want to start the range with?"
>
> count =3D gets.to_i

puts prints a string (I think it stands for "PUT String"), and gets
(conincidentally enough) gets a string.  It defaults to getting it
from standard input/output (which is the terminal if you're running
the program in the shell without redirecting input), but you can make
it put/get input from any IO object, like a file, network socket, etc
(see the IO documentation for more).

> sum =3D count

It doesn't look like you use sum.. maybe leftover from a previous
incarnation of the program?

> puts " How many ip addresses do you want?"
>
> number =3D gets.to_i
> number =3D number - 1
> puts "Enter the first three parts of the ip-address (for example
> 192.168.4. )"
> range =3D gets.chomp

Chomp is like chomp in perl;  it takes the newline off the end of the
string if it happens to have one.

> puts "Do you want to put some text in front of the ip-address? Put it her=
e"
> textbefore =3D gets.chomp
>
> puts "Do you want to put some text after the ip-address? Put it here"
> textafter =3D gets
>
> puts textbefore + range + count.to_s + textafter
>
> number.times do
>         count +=3D1
>         sum +=3D count
>         puts textbefore + range + count.to_s + textafter
> end

There are a few ways to rearrange the loop that might (or might not be) cle=
arer.

First, if you take away the 'number =3D number-1' line, I think you
could also take away the first puts outside of the loop, and do:

number.times do
  puts textbefore + range + count.to_s + textafter
  count +=3D1
  sum +=3D count
end

Or, you could do something like this (which we'll learn about mostly
in Lesson 2 in the Expressions chapter of the book):

start =3D count
end =3D count + number - 1
start.upto(end) do |current_number|
  puts textbefore + range + current_number.to_s + textafter
end

(I haven't tried it so there's probably an off by one error)

The upto method (in the Integer class) does the stuff in the do/end
for every integer from start up to end.

Also, a different way to create strings:  This code would do the same thing=
:

puts "#{textbefore}#{range}#{count}#{textafter}"

(and it would call the count.to_s for you).  We'll see this first in Lesson=
 1.

--
Laurel Fan
http://dreadnought.gorgorg.org

From wallachd@earthlink.net  Mon Nov 28 09:46:25 2005
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        homework assignment
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Laurel Fan wrote:
> = Lesson 0: Installing and Documentation References
[snip]
> == Homework
[snip]
> 
> First, introduce yourself.  Do you know any other programming
> languages?  What do you like/not like about them?  Why are you
> interested in Ruby?  What are some things you'd like to learn to do?
> 

Hi,

Laurel - thank you for the Ruby course!

My name is Darlene. I'm getting a late start on the Ruby course.
I'm an unemployed software engineer who did most of my work using
"C" and korn shell scripts.

I used to be very passionate about software but since returning
from almost 2 months in Palestine in 2002, I've been more passionate
about Palestine and other related political issues. I'm trying to
get my feet back in the software arena.

I heard good things about Ruby and kind of got an introduction last year 
with a hands-on Ruby track with the Silicon Valley Patterns group. I'm 
interested in learning Ruby and using it. I'm recently read Ruby on 
Rails articles in the Linux Journal by Reuven Lerner. Rails seems very 
impressive too.

> Second, find and run any ruby program.  It can be something you wrote,
> something you downloaded (hint, look on RubyForge), an example you
> copied out of a book, something a friend wrote for you, etc.
> 
> Finally, look at the code.  Find a section of about 5-20 lines of
> code, and try to figure out what it does.  If you figure it out (or
> just have a good guess), explain it to us.  If not, show us the code
> and we'll try to explain it.
> 

Here is one of the ruby scripts from execises during the Ruby track
last year:
# Define a method named "even" which takes one argument, an array of
# integers, and which returns an array consisting of the even integers
# (if any) from the argument array.

class ExerciseE
         def even(startArray)
           evenArray = Array.new()
           startArray.each do |x|
             if (x % 2) == 0
               evenArray.push(x)
             end
           end
           return evenArray
         end
end


-- 
World Centric Fair Trade & Eco Store
http://www.worldcentric.org/store/
We have created and live in a world of gross social
and economic inequalities[1] and are at the same
time severely impacting[2] the natural eco-systems
and regenerating bio-capacity of the planet. Our
every action has an impact on the well-being of our
planet and our everyday decisions[3] can help create
a better world for all. In keeping with this fact
and our vision, the World Centric Fair Trade/Eco
Online Store provides everyday consumption choices,
which can help minimize social & economic
inequalities, reduce the impact of our consumption
on the environment and help create a better and
sustainable world.

[1] http://www.worldcentric.org/stateworld/socialjustice.htm
[2] http://www.worldcentric.org/stateworld/environment.htm
[3] http://www.worldcentric.org/sustain/index.htm

From anne@wjh.harvard.edu  Sat Nov 12 07:56:57 2005
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Date: Fri, 11 Nov 2005 15:43:42 -0500 (EST)
From: Anne G <anne@wjh.harvard.edu>
To: <courses@linuxchix.org>
Subject: [Courses] [Ruby] Lesson 0: Installing
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Hi

My name is anne. I have been programming in C and matlab. I
started to learn objective C, but I am really stumped by how
big a step I have to take, and I keep getting mad... How is
this supposed to be the next thing after C. There are way
too much idiosynchratic tricks to learn, I hate the whole
memory management, beginners like me should not have to
deal with it...

So I am delighted to try if rubi will ease the way.

First I just spend hours and hours on the install on my mac.
First, the latest rubi is 1.8.3

I found the source easily enough, but I could not find an
install application for it, and I did not know what to do
with the source. Luckily, I found a blog that saved me,
http://www.downes.ca/cgi-bin/page.cgi?post=31620
I went into the directory in the terminal window, ls ...
than I think I ran
./configure
make
sudo make install
(I had missed his instruction to become superuser, and got
an error message, permission denied at first).

rubi -v
does give me 1.8.3 version.

the application for rubicocoa was easier to find
http://rubycocoa.sourceforge.net/
I downloaded and installed the one for panther.
When I ran xcode, rubi is one of the options. I don't know
how to tell if it is the right version.

I did not try to install ruby on rails for now.

I found a tutorial on rubycocoa
http://rootprompt.org/article.php3?article=7785
and I am working my way through, but it is beyond what I
want to do right now.

I just want to run some simple code, and I don't know where
to put the code in all the files.

There is a main.m file which I think you don't usually
touch. there is an rb_main.rb file which probably is the one
to use.

require 'osx/cocoa'

def rb_main_init
  path =
OSX::NSBundle.mainBundle.resourcePath.fileSystemRepresentation
  rbfiles = Dir.entries(path).select {|x| /\.rb\z/ =~ x}
  rbfiles -= [ File.basename(__FILE__) ]
  rbfiles.each do |path|
    require( File.basename(path) )
  end
end

if $0 == __FILE__ then
  rb_main_init
  OSX.NSApplicationMain(0, nil)
end


I don't think I need to know what this says, but I do need
to know where to put a rubi instruction, such as type "hello
world"... Does anyone know?

I understand that coco+rubi may be adding more complexity
then I am supposed to have, but I an xcode environment
should be much more pleasant than text files and terminal
window compilation. So if I can figure how to do straight
rubi code and then cocoa code in the same environment, it
seems worth the extra effort




From anne@wjh.harvard.edu  Tue Nov 15 01:10:51 2005
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Date: Mon, 14 Nov 2005 09:10:45 -0500 (EST)
From: Anne G <anne@wjh.harvard.edu>
To: <courses@linuxchix.org>
Subject: Re: [Courses] [Ruby] Lesson 0: Homework
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The course web site is back, yeah.

I figured out how to run ruby with rubycocoa. I just add a
ruby file, erase the lines about a class, and enter the ruby
code. It compiles, and prints in the run log window.

Here is my homework. I cheated and found a snipet of
text which makes sense to me, and also has a commentary
http://redhanded.hobix.com/inspect/thinStrandOfSearchAndReplaceRails.html
the snipet was taken from somewhere else, and I added print
to see what it does.

def quicksort( xs )
   puts "Iterations, array size = "
   puts xs.size
   puts "Print the array"
   puts xs
   return xs if xs.size <= 1
   m = xs[0] # Split-Element
   quicksort(xs.select { |i| i < m } ) +
     xs.select { |i| i == m } +
     quicksort(xs.select { |i| i > m } )
end
puts "Final array"
puts quicksort([13, 11, 74, 69, 0])
puts "hello we are done"

Here is the comment
-----------------------------------------------------------------
line by line:

  return xs if xs.size <= 1


If the size is 1 or 0, we just return the array; it's already sorted

  m = xs[0]

Here we choose an arbitrary "Pivot" element.
This can be any element of the array. In this case we choose
the first.

  quicksort(xs.select { |i| i < m } ) +
     xs.select { |i| i == m } +
     quicksort(xs.select{ |i| i > m } )

This is a little more complicated. First, let's figure out
what those selects do. The first one selects all elements
less than the pivot. The second selects all elements equal
to the pivot. The final one selects all elements greater
than the pivot. Let's modify this and use some temp variables.

  less = xs.select { |i| i < m }
  equal = xs.select { |i| i == m }
  more = xs.select { |i| i > m }

  quicksort( less ) +
    equal +
    quicksort( more ) )


In other words, we're returning a list of all the elements
less than the pivot, sorted, then all those equal, then all
those greater, sorted. This is classic divide-and-conquer
recursion. Quicksort is applied to ever smaller lists until
we use it on lists of one or zero elements, and we hit the
terminating condition.

-----------------------------------------------------------
the xs.select is equivalent to the find function in matlab.

xs.select { |i| i < m }
|i| must mean for each element of xs compare it to m
what is confustin to me is I usually use i as an index, but
since m=xs[0], i must be an array element.

-----------------------------------------------------------
I have never used recursion like this, it is very efficient,
but I wonder about readability!

Thank you so much for this course. Finding this little
snipet and running it was fun. And it was interesting to see
what others have found

Anne



From laurel.fan@gmail.com  Sat Nov 19 05:18:41 2005
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Date: Fri, 18 Nov 2005 10:18:34 -0800
From: Laurel Fan <laurel.fan@gmail.com>
To: Anne G <anne@wjh.harvard.edu>
Subject: Re: [Courses] [Ruby] Lesson 0: Homework
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On 11/14/05, Anne G <anne@wjh.harvard.edu> wrote:
Hi Anne!

Great example implementation of quicksort.  It shows off one of the
unique features of ruby, which is the block syntax (the { |i| i < m }
stuff).  There's more about blocks in the book, and this interview
with the language designer (Yukihiro "Matz" Matsumoto) gives a little
more background:

http://www.artima.com/intv/closures.html

> def quicksort( xs )
>    puts "Iterations, array size =3D "
>    puts xs.size
>    puts "Print the array"
>    puts xs
>    return xs if xs.size <=3D 1
>    m =3D xs[0] # Split-Element
>    quicksort(xs.select { |i| i < m } ) +
>      xs.select { |i| i =3D=3D m } +
>      quicksort(xs.select { |i| i > m } )
> end
> puts "Final array"
> puts quicksort([13, 11, 74, 69, 0])
> puts "hello we are done"
>
> Here is the comment
> -----------------------------------------------------------------
> line by line:
>
>   return xs if xs.size <=3D 1
>
>
> If the size is 1 or 0, we just return the array; it's already sorted
>
>   m =3D xs[0]
>
> Here we choose an arbitrary "Pivot" element.
> This can be any element of the array. In this case we choose
> the first.
>
>   quicksort(xs.select { |i| i < m } ) +
>      xs.select { |i| i =3D=3D m } +
>      quicksort(xs.select{ |i| i > m } )
>
> This is a little more complicated. First, let's figure out
> what those selects do. The first one selects all elements
> less than the pivot. The second selects all elements equal
> to the pivot. The final one selects all elements greater
> than the pivot. Let's modify this and use some temp variables.
>
>   less =3D xs.select { |i| i < m }
>   equal =3D xs.select { |i| i =3D=3D m }
>   more =3D xs.select { |i| i > m }
>
>   quicksort( less ) +
>     equal +
>     quicksort( more ) )
>
>
> In other words, we're returning a list of all the elements
> less than the pivot, sorted, then all those equal, then all
> those greater, sorted. This is classic divide-and-conquer
> recursion. Quicksort is applied to ever smaller lists until
> we use it on lists of one or zero elements, and we hit the
> terminating condition.
>
> -----------------------------------------------------------
> the xs.select is equivalent to the find function in matlab.
>
> xs.select { |i| i < m }
> |i| must mean for each element of xs compare it to m
> what is confustin to me is I usually use i as an index, but
> since m=3Dxs[0], i must be an array element.

Yes, you're right.  If you use matlab, you might like all the
functions on Enumerable (like select), since they kind of resemble
doing vector operations.

> -----------------------------------------------------------
> I have never used recursion like this, it is very efficient,
> but I wonder about readability!

Sometimes I find it more readable to use the long form, such as:

xs.select do |i|
  i < m
end

In any case, I think it takes some getting used to.  It's not as
immediately intuitive as some concepts (like if/else).  I think there
are lots of cases when it's more readable than doing it without it.=20
When you do a sort in C, and want to define your own comparison
function, you have to define a function separately and make a function
pointer;  in other OO languages like C++ and Java, the same thing
might require making a completely different object.



--
Laurel Fan
http://dreadnought.gorgorg.org

From anne@wjh.harvard.edu  Fri Nov 18 09:32:29 2005
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From: Anne G <anne@wjh.harvard.edu>
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Hi

I started thinking about lesson 1, but I am spending most of
my time reading about set ups.

I would like to look at ruby class methods, but I have not
figured out how to do that. there is something called ri
which is a terminal program but I have not really figured
out how to use it to look at class methods, what they do...

could someone post some examples of how to use ri, or any
other tool that would be useful in that regard?

for objective C there was a nice little application
AppKiDo 0.94 which let you look at classes, methods...

In xcode there were ways to use key combinations to find
definitions... What is the best way -- beside the book which
should come next week -- to find out information

-------------------------------------------------------

I have also been thinking about GUI and how to do that in
Ruby for a web application. I found an example using tk

Here is the snipet I found which makes a button:

require 'tk'
root = TkRoot.new
button = TkButton.new(root) {
  text "Hello,Anne"
  command proc { puts "I said"}

}

button.pack
Tk.mainloop

It runs on ruby terminal, but it does not run on rubycocoa,
and it does not run on emacs.

I would really like to be set up in an environement where I
don't have to use terminal and unix commands. I would like
to use mac applications, mac windows and editors. I don't
know what to do to get a set up I will be able to use with
GUIs if this basic one does not work!

Any idea why rubycocoa and emacs don't find tcltklib?
It is a directory in ext in the ruby 1.8.3 source file, but
I don't know what happens to it during install or how to
set up a mac path so ruby finds it in those other
environments

------------------------------------------------------

In addition, I got a response which suggest GUIs are quite
complex and I don't know which package I should use, if it
is set up by default or not...

Here is the response:
> rubycocoa is the Ruby interface bindings to the native
> cocoa GUI toolkit of the Mac.  tcl is a scripting
> language and its standard GUI toolkit is tk that uses
> non native widgets - i.e. has its own unique look and
> feel.  tclTkAqua is the tcl Tk toolkit that uses native
> Mac widgets The tk toolkit is widely ported and many
> other bindings to it have been produced, including Ruby.

> If you are using rubycocoa then it doesn't make sense to
> me why you would want to use tcl, tk or tckTkAqua as you
> are trying to mix different GUI toolkits.

What guis will we be using for this course?

thanks for any help you can give me.

Anne
PS
my two posts on comp.lang.ruby

http://groups.google.com/group/comp.lang.ruby/browse_frm/thread/b68d9da3118402c1
http://groups.google.com/group/comp.lang.ruby/browse_frm/thread/dd608f51c6f47e9e/b00540532449bd8f#b00540532449bd8f



From anne@wjh.harvard.edu  Sun Nov 20 04:18:32 2005
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Date: Sat, 19 Nov 2005 12:17:52 -0500 (EST)
From: Anne G <anne@wjh.harvard.edu>
To: <courses@linuxchix.org>
Subject: Re: [Courses] [Ruby] Lesson 0: Installing
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> I'm not planning to do any GUI programming in this course.

OK, that's fine. I need to figure out how to do Object
oriented programming, and it is probably better not to
get involved with GUIs right now. Because lesson 1 talked
about showing pictures, I assumed we would need an
interface... and started looking in that direction.

---------------------------------------------------

I did get emacs to work with my button snipet with tk.
it now works. If anyone is interested, here is the
discussion
http://groups.google.com/group/gnu.emacs.help/browse_frm/thread/751afb08ac720d06/0468760d41b3c2a6?lnk=raot#0468760d41b3c2a6

It has to do with conflict between two installations of ruby
on the same computer, (1.6 that comes with panther, and
1.8.3 I installed )  and setting the path.

So now, on to lesson 1!

Anne


From laurel.fan@gmail.com  Tue Nov 15 17:47:18 2005
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From: Laurel Fan <laurel.fan@gmail.com>
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Subject: [Courses] [Ruby] Lesson 1: Introduction, Classes, Objects,
        and Variables
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=3D Lesson 1: Introduction, Classes, Objects, and Variables

=3D=3D Reading

If you're using the second edition on paper or pdf, the reading is ....

If you're using the first edition on the web, the reading is the
following sections:

Foreword: http://www.rubycentral.com/book/foreword.html
Preface: http://www.rubycentral.com/book/preface.html
Roadmap: http://www.rubycentral.com/book/roadmap.html
Ruby.new: http://www.rubycentral.com/book/intro.html
Classes, Objects, and Variables:  http://www.rubycentral.com/book/tut_class=
es.ht
ml

(Don't worry, the first three links are introductory material for the
book itself...)

=3D=3D Homework

(As usual, you can of course do as much or as little as you like.  If
you don't have time to answer every single question, you should still
post what you have done)

=3D=3D=3D Questions

1. Any questions about the reading?  Anything that you didn't
   understand, or want to know more about?

2. For those who know other programming languages, what are some ways
   that Ruby is different from other languages you know?

3. What's the difference between an instance variable and class
   variable?

4. What's the difference between a variable and an attribute?

=3D=3D=3D Problems

1. Defining classes: photo gallery.  Think about what classes you
   would need to define to write a web photo gallery application.  For
   now, don't think of the actual implementation details of handling
   web requests, displaying images, etc.  Obviously you'll need to
   represent a photo.  What attributes does it have?  What other
   objects do you need?
post what you have done)

=3D=3D=3D Questions

1. Any questions about the reading?  Anything that you didn't
   understand, or want to know more about?

2. For those who know other programming languages, what are some ways
   that Ruby is different from other languages you know?

3. What's the difference between an instance variable and class
   variable?

4. What's the difference between a variable and an attribute?

=3D=3D=3D Problems

1. Defining classes: photo gallery.  Think about what classes you
   would need to define to write a web photo gallery application.  For
   now, don't think of the actual implementation details of handling
   web requests, displaying images, etc.  Obviously you'll need to
   represent a photo.  What attributes does it have?  What other
   objects do you need?

2. Defining classes: /proc. (This might not be as interesting for
   windows users).  On unix, the /proc filesystem is a virtual
   filesystem containing information about the running processes
   (among other things).  It contains a directory for each running
   process, which contains information about the process, such as the
   command line, the amount of memory it's using, etc).  Define a set
   of classes to represent the process data in /proc.

Bonus: Actually write a program to look at the data in proc and do
something with it.  A good start would be to print out the pids and
command lines.  You might want to look up the File and Dir classes.

Thats it, Lesson 2 (covering chapters 4-6: Containers, Blocks, and
Iterators; Standard Types; More About Methods) will be posted Nov 28
(in 2 weeks).

--
Laurel Fan
http://dreadnought.gorgorg.org

From akkana@shallowsky.com  Sun Nov 27 17:04:13 2005
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From: Akkana Peck <akkana@shallowsky.com>
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Subject: Re: [Courses] [Ruby] Lesson 1: Introduction, Classes, Objects,
        and Variables
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Laurel Fan writes:
> 2. For those who know other programming languages, what are some ways
>    that Ruby is different from other languages you know?

The biggest difference is that everything is a class -- even
numbers. Being able to say something like -1942.abs instead of
abs(-1942) or Math.abs(-1942) is neat. I like it. One of the
confusing things about Python (though I do like Python a lot)
is figuring out, especially with strings, when I need to say
s.replace("foo", "bar") vs. string.replace(s, 'foo', 'bar');
or sometimes needing to say something like Integer(-1942).abs
(i.e. some things are already an object, but other things you
have to convert into an object). Ruby is more consistent.

The expression interpolation is cool, too: being able to say
puts "Good night, #{name}", where name is the name of one of
the function arguments, is very useful.

One thing I don't like as much is the if ... elsif ... end
structure. To be honest. I like C-style braces best, though
Python's colon-plus-indentation works well too. "end" isn't
so bad, but as someone who uses lots of different languages,
it drives me batty to try to remember which languages use
"else if", which "elif", which "elsif", etc. ... and I wish
people would just stop designing languages that way.

Blocks and "yield" seem like an unnecessary complexity, but
perhaps eventually I'll see the point. (The examples in the
book don't really justify why this is needed.)

> 3. What's the difference between an instance variable and class
>    variable?

An instance variable belongs to a specific object (an instance
of some class). Each instance has its own copy of each instance
variable. A class variable is shared by the whole class; the whole
class only has one copy, and each instance of the class can see
the value of that class variable.

> 4. What's the difference between a variable and an attribute?

Attributes look like instance variables to code outside the class,
but they're actually implemented as functions (sometimes? Always?)
If you use attr_reader (or do the same thing by hand), then the
function that implements the attribute that's visible outside
the class will probably just return the value of the instance
variable of the same name.

> 1. Defining classes: photo gallery.  Think about what classes you
>    would need to define to write a web photo gallery application.  For
>    now, don't think of the actual implementation details of handling
>    web requests, displaying images, etc.  Obviously you'll need to
>    represent a photo.  What attributes does it have?  What other
>    objects do you need?

Okay, just a quick start on this.
(Note: I have my own simple web photo gallery code, a really basic
setup, that I wrote in perl a long time ago and later translated
into PHP. So I've thought about this a little, though my
implementation is just a bare-bones one and doesn't do most
of what I'll suggest here.)

The only thing the photo object absolutely needs to have is the
filename (the thing that's going to go into the IMG tag in the page).

But there are some other things it really ought to have:

* Something to put in the ALT attribute of the IMG tag on the page
  (a few words of description).
* A longer description (may be blank) describing what the photo is.
* Width and Height of the image.
* EXIF information, if any (date/time, size, what camera was used,
  exposure data like aperture and shutter speed)
* Other sizes which might be available (thumbnail? fullres?)
* Maybe information on copyright or how to order a print,
  depending on the intended user of the gallery.

Other objects:
* gallery: information about this particular gallery, mainly a
  title indicating what the pictures are, like "Vacation in Hawaii",
  maybe a date, maybe some descriptive text, maybe cross-references
  to other similar galleries like "Vacation in Tahiti".
* Some way to store links back to the top level, and possibly
  to other galleries. That might belong in the gallery object too,
  but there might be other navigation information needed which
  might justify some other object.
* Something that can handle layout: things like how many images can
  we display per row, and where are we in the row?

I haven't done anything on the /proc suggestion -- though it does
sound like a fun exercise. But I ran out of time and decided it
was better to post what I had than keep it sitting any longer
waiting until I had time to fiddle with /proc.

        ...Akkana

From laurel.fan@gmail.com  Fri Nov 18 09:43:52 2005
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From: Laurel Fan <laurel.fan@gmail.com>
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Subject: [Courses] [Ruby] GUIs (Was: Lesson 0: Installing)
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On 11/17/05, Anne G <anne@wjh.harvard.edu> wrote:
> What guis will we be using for this course?

Are you looking for a GUI application for you to use to write ruby
code?  Or are you talking about creating grapical programs with ruby?=20
I don't have any experience with either, and I'm not planning to do
any GUI programming in this course.

However, there is nothing to stop you from using any graphical editor
or IDE that you wish to write your code (I can't help you with
specifics because I haven't used any.. I use emacs with ruby-mode).=20
If you're not interested in doing anything at all with the terminal,
this may not be the course for you, unless someone else here can help
you figure that out...

--
Laurel Fan
http://dreadnought.gorgorg.org

From anne@wjh.harvard.edu  Thu Nov 24 05:41:27 2005
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From: Anne G <anne@wjh.harvard.edu>
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Happy Thanksgiving, for those who celebrate it.

I have a project I am working on, parsing subject data that
has been concatennated into one giant file. I figure I can
write a class and small methods as an exercise...

but it is just as easy to process the file line by line with
a few switches here and there, without specifying any new
class (other than an array instance etc)..

The song example in the book is a database.  What are other
examples of common objects? When is it worth creating an
object, versus plain code?

I understand the theory about encapsulation, but in practice
my code is fairly short, and I only use functions to
identify what different sections of the code do. I use
globals to avoid the hastle of passing info to the fxs.

so I don't really know, how do you figure out what part
of the code would be a good candidate for a class.

Anne





From anne@wjh.harvard.edu  Sun Nov 27 01:19:58 2005
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Subject: Re: [Courses] [Ruby] Lesson 1: Classes 
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> You can spend a bit of time at the beginning of a course
> having students use programs which emphasize the
> interactions between objects. Students need to have
> clear ideas about objects, messages, behavior, and
> state.

I can't find any information about how to have objects
interact.

Most of the examples are about sending a method to an object
from the program. I can't find an example of an object
sending a message to an other object.

How do you get an object to send a message to an other
object given that the objects don't yet exist when the
classes and instance method are defined in the code?

thanks

Anne


From laurel.fan@gmail.com  Sun Nov 27 07:14:20 2005
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Date: Sat, 26 Nov 2005 12:07:51 -0800
From: Laurel Fan <laurel.fan@gmail.com>
To: Anne G <anne@wjh.harvard.edu>
Subject: Re: [Courses] [Ruby] Lesson 1: Classes
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On 11/26/05, Anne G <anne@wjh.harvard.edu> wrote:
> I can't find any information about how to have objects
> interact.
>
> Most of the examples are about sending a method to an object
> from the program. I can't find an example of an object
> sending a message to an other object.
>
> How do you get an object to send a message to an other
> object given that the objects don't yet exist when the
> classes and instance method are defined in the code?

I'm not quite clear on what you're asking, but I think you might be
over thinking it a little.  The other objects don't need to exist when
you are defining the methods, only when the method is actually called.
 Methods can call methods on other objects pretty much whenever they
feel like.  Let's say I'm writing a program to control my smart
fridge.


class Fridge
  def init
    @milk_cartons =3D Array.new()
  end

  def add_milk_carton(carton)
    @milk_cartons.add
  end

  def has_milk?
    @milk_cartons.each do |carton|
      if !carton.empty?
        return true
      end
    end
    false
  end
end

In this case, the has_milk? function sends a message to the object
that we're using to represent milk cartons.  We haven't defined that
object yet, but as long as it's defined by the time we run the program
and call the function, it'll work fine.

This is something that's mostly unique to ruby:  Most of the time, it
doesn't matter what the actual type/class of an object is.  It only
matters what methods it responds to.  For example, in this case, we
could define a new MilkCarton class that implements the empty? method,
but if we're feeling lazy we could use a String (since String
implements empty? as well).

There's even a special method called method_missing that is called on
an object when we try to send it a message (ie. call a method) that it
doesn't understand.  This lets you implement methods without actually
implementing them.  The book has a toy example of what you can do with
this:

http://www.rubycentral.com/book/ref_c_object.html#Object.method_missing

Thanks for all of your questions (let me know if this wasn't clear or
didn't answer your question)!

--
Laurel Fan
http://dreadnought.gorgorg.org

From anne@wjh.harvard.edu  Sun Nov 27 07:53:07 2005
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From: Anne G <anne@wjh.harvard.edu>
To: <courses@linuxchix.org>
Subject: Re: [Courses] [Ruby] Lesson 1: Classes
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Here is the example I am thinking about:

I define a class with two class variables and a storage
array, and I create two instances
datainst=dataClass.new
infoinst=dataClass.new

the objects datainst and infoinst both have access to @@Arr
and @@ind, and each have their own array.

class dataClass
     def initialize
        @@Arr=array read from file, constant
        @@ind=0
        @storeAr=[]
     end
end

I can get my program rolling by calling a method, say
datainst.lookforX

class dataClass
    def lookforX
        look for X in @@arr[@@ind]
        if X not found
            increase @@ind
            Self.lookforX
        else X is found
            Send a message to the other object to tell it
its its turn to do something   ?????  HOW DO I DO THAT?
            break out of all recursions
        end
    end
end

The object datainst can call itself with Self but how does
object 'datainst' tell object 'infoinst' that it is its turn
to be processing the array?

In Sams learning ruby, it says that you can define a method
for an object.
def datainst.lookforX
     ...
     else X is found
         infoinst.getinfo
         break out of all recursions
     end
   end
end
def infoinst.getinfo
...
end

Is this the way to go to get two objects to talk to each
other?

anne


From laurel.fan@gmail.com  Tue Nov 29 05:04:16 2005
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From: Laurel Fan <laurel.fan@gmail.com>
To: Anne G <anne@wjh.harvard.edu>
Subject: Re: [Courses] [Ruby] Lesson 1: Classes
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Comments inline (I hope you don't mind the lack of snipping, I wanted
to preserve the whole context).

On 11/26/05, Anne G <anne@wjh.harvard.edu> wrote:
> Here is the example I am thinking about:
>
> I define a class with two class variables and a storage
> array, and I create two instances
> datainst=3DdataClass.new
> infoinst=3DdataClass.new
>
> the objects datainst and infoinst both have access to @@Arr
> and @@ind, and each have their own array.
>
> class dataClass
>      def initialize
>         @@Arr=3Darray read from file, constant
>         @@ind=3D0
>         @storeAr=3D[]
>      end
> end
>
> I can get my program rolling by calling a method, say
> datainst.lookforX
>
> class dataClass
>     def lookforX
>         look for X in @@arr[@@ind]
>         if X not found
>             increase @@ind
>             Self.lookforX
>         else X is found
>             Send a message to the other object to tell it
> its its turn to do something   ?????  HOW DO I DO THAT?
>             break out of all recursions
>         end
>     end
> end
>
> The object datainst can call itself with Self but how does
> object 'datainst' tell object 'infoinst' that it is its turn
> to be processing the array?

It needs a reference to infoinst.  If you defined the lookForX
function to take another object as an argument, you could pass it
infoinst.  For example:

class dataClass
     def lookforX(other) ## this tells us that lookforX takes 'other'
as an argument
         look for X in @@arr[@@ind]
         if X not found
             increase @@ind
             Self.lookforX
         else X is found
             other.doSomethingElse ## this calls lookforX on other.=20
We pass it nil because lookforX takes an argument
             Send a message to the other object to tell it
 its its turn to do something   ?????  HOW DO I DO THAT?
             break out of all recursions
         end
     end

    def doSomethingElse
    ...   ## infoinst is the same class as datainst, so we could
define the doSomethingElse method here
   end
 end

Then, when you call the lookforX method, you would do something like:

datainst.lookforX(infoinst)

This calls lookforX on datainst, and passes it a reference to
infoinst.  So, if you look at the new lookforX definition, it calls
"other.doSomethingElse".  Since other is infoinst, this calls
infoinst.doSomethingElse.

> In Sams learning ruby, it says that you can define a method
> for an object.
> def datainst.lookforX
>      ...
>      else X is found
>          infoinst.getinfo
>          break out of all recursions
>      end
>    end
> end
> def infoinst.getinfo
> ...
> end
>
> Is this the way to go to get two objects to talk to each
> other?

Not necessarily.  Defining methods for objects (instead of for
classes) can sometimes be useful, but usually if we want objects to
have different methods we make them different classes.  Passing
references to other objects is the usual way of having objects talk to
each other.

--
Laurel Fan
http://dreadnought.gorgorg.org

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From: Laurel Fan <laurel.fan@gmail.com>
To: Anne G <anne@wjh.harvard.edu>
Subject: Re: [Courses] [Ruby] Lesson 1: Classes
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On 11/23/05, Anne G <anne@wjh.harvard.edu> wrote:
> I have a project I am working on, parsing subject data that
> has been concatennated into one giant file. I figure I can
> write a class and small methods as an exercise...
>
> but it is just as easy to process the file line by line with
> a few switches here and there, without specifying any new
> class (other than an array instance etc)..

It's true that very simple programs such as this are probably just as
easily done procedurally as with objects.

> The song example in the book is a database.  What are other
> examples of common objects? When is it worth creating an
> object, versus plain code?

One way of thinking of this is whether something is represented as an
object in a real world, or whether it has multiple properties.  A few
examples:

If I was writing a jigsaw puzzle game, I could make each piece an
object, with properties such as the image on the piece, and the shapes
of the sides.  I could also imagine creating methods to determine
whether two pieces fit together, or to attach two pieces.  To get more
fancy, since I realize that a set of pieces that are already put
together share many of the same properties as a single piece, I could
even make them share some methods and functionality with inheritance
and mixins.

If I was writing a http server, an http request has several
properties, such as the URL, query string, user agent (the type of
browser making the request), even things such as the time of the
request.  I'd like to keep these together in the same object.  One of
the advantages of this is that when writing functions that use some of
this information, I can simply pass the whole request object instead
of individual properties.  Or, when it makes sense, I can put the
methods on my HTTPRequest class.

> I understand the theory about encapsulation, but in practice
> my code is fairly short, and I only use functions to
> identify what different sections of the code do. I use
> globals to avoid the hastle of passing info to the fxs.
>
> so I don't really know, how do you figure out what part
> of the code would be a good candidate for a class.

For small programs especially, it can be hard to tell whether using
classes gives you any advantage.  It's definitely a lot more obvious
for larger programs;  that's one of the things that makes teaching
object oriented programming difficult.

--
Laurel Fan
http://dreadnought.gorgorg.org

From anne@wjh.harvard.edu  Fri Dec  2 00:29:27 2005
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From: Anne G <anne@wjh.harvard.edu>
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Subject: Re: [Courses] [Ruby] Lesson 1: Classes
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Thank you so much Laurel for your response. I will review
classes, and do the reading on lesson2 as you suggested.

First of all your suggestion expended my thinking to include
passing of an object. Thank you so much.

datainst.lookforX(infoinst)

I took this idea and tried to generalize it to 3 objects:

object1 -- stores data,  calls on object2 -- stores first
type of info, calls on object3 -- stores 2nd type of info,
calls back on object1.

I found myself doing the following:

storeobject.lookforX(info1object,info2object,storeobject)

this way lookforX knows to call on info1object
info1object knows to call on info2object
info2object knows to call on storeobject
...

I love this solution because it is totally within the scope
of what I can do. but it is a bit heavy and still smacks of
procedural in that I have to figure out what the whole chain
of objects will be instead of just relation between
pairs of objects.

Is this the way your suggestion would work with 3 objects?

---------------------------------------------------------

I found this recent discussion
http://groups.google.com/group/comp.lang.ruby/browse_frm/thread/68acf0f7c8a95138/1bbd14c18a57a45b#1bbd14c18a57a45b

Daniel Schierbeck offered a structure which seems simple
enough, and probably similar to yours, but it is a bit
confusing to my beginner's eye. What is hapening?

Here is what he said

Say you have three classes, A, B, and C, and you want their
instances to be able to communicate. These three classes
will all be instantiated together, so we know that the other
objects are there. You then write a class, let's just call
it Base, that you instantiate instead of the three classes.
It will instantiate them instead, and pass a reference to
itself to each of them.

   class Base
     attr_reader :a, :b, :c

     def initialize
       @a, @b, @c = A.new(self), B.new(self), C.new(self)
     end

     # We'll keep the other classes in here, so we don't
     # pollute the main namespace
     class A
       def initialize(base)
         @base = base
         @b, @c = base.b, base.c
       end
     end

     class B
       def initialize(base)
         @base = base
         @a, @c = base.a, base.c
       end
     end

     class C
       def initialize(base)
         @base = base
         @a, @b = base.a, base.b
       end
     end
   end

How would I use this in my expended task:
objectA needing to call on objectB needing to call on
objectC needing to call back on objectA

Thank you so much for running this course.

anne




From laurel.fan@gmail.com  Sat Dec  3 05:01:00 2005
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Date: Fri, 2 Dec 2005 10:00:56 -0800
From: Laurel Fan <laurel.fan@gmail.com>
To: Anne G <anne@wjh.harvard.edu>
Subject: Re: [Courses] [Ruby] Lesson 1: Classes
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On 12/1/05, Anne G <anne@wjh.harvard.edu> wrote:
> Thank you so much Laurel for your response. I will review
> classes, and do the reading on lesson2 as you suggested.
>
> First of all your suggestion expended my thinking to include
> passing of an object. Thank you so much.
>
> datainst.lookforX(infoinst)
>
> I took this idea and tried to generalize it to 3 objects:
>
> object1 -- stores data,  calls on object2 -- stores first
> type of info, calls on object3 -- stores 2nd type of info,
> calls back on object1.
>
> I found myself doing the following:
>
> storeobject.lookforX(info1object,info2object,storeobject)
>
> this way lookforX knows to call on info1object
> info1object knows to call on info2object
> info2object knows to call on storeobject
> ...
>
> I love this solution because it is totally within the scope
> of what I can do. but it is a bit heavy and still smacks of
> procedural in that I have to figure out what the whole chain
> of objects will be instead of just relation between
> pairs of objects.
>
> Is this the way your suggestion would work with 3 objects?

All of these objects can store information.  So you could pass in the
other object once, and then the object can save it to use later.  So
for example, when you instantiate the objects, you could do:

-----

storeObject =3D StoreObject.new()
infoInst1 =3D InfoObject.new()
infoInst2 =3D InfoObject.new()

infoInst1.helper =3D infoInst2
infoInst2.helper =3D storeObject

infoInst1.lookForX # we don't need to pass the other objects here,
because it remembered it from above

-----
The setHelper function itself remembers its argument with an @
variable, something like:
-----
classInfoObject
...
attr_accessor :helper # this makes a method helper that allows you do
set the variable @helper
...
end

-----
And then lookForX would look kind of like
-----
def lookForX
   ...
   @helper.lookForX
   ...
end


> ---------------------------------------------------------
>
> I found this recent discussion
> http://groups.google.com/group/comp.lang.ruby/browse_frm/thread/68acf0f7c=
8a95138/1bbd14c18a57a45b#1bbd14c18a57a45b
>
> Daniel Schierbeck offered a structure which seems simple
> enough, and probably similar to yours, but it is a bit
> confusing to my beginner's eye. What is hapening?
>
> Here is what he said
>
> Say you have three classes, A, B, and C, and you want their
> instances to be able to communicate. These three classes
> will all be instantiated together, so we know that the other
> objects are there. You then write a class, let's just call
> it Base, that you instantiate instead of the three classes.
> It will instantiate them instead, and pass a reference to
> itself to each of them.
>
>    class Base
>      attr_reader :a, :b, :c
>
>      def initialize
>        @a, @b, @c =3D A.new(self), B.new(self), C.new(self)
>      end
>
>      # We'll keep the other classes in here, so we don't
>      # pollute the main namespace
>      class A
>        def initialize(base)
>          @base =3D base
>          @b, @c =3D base.b, base.c
>        end
>      end
>
>      class B
>        def initialize(base)
>          @base =3D base
>          @a, @c =3D base.a, base.c
>        end
>      end
>
>      class C
>        def initialize(base)
>          @base =3D base
>          @a, @b =3D base.a, base.b
>        end
>      end
>    end
>
> How would I use this in my expended task:
> objectA needing to call on objectB needing to call on
> objectC needing to call back on objectA

This is pretty similar to what I wrote above, but it looks nicer
because all the initialization happens inside the Base class.  In the
above code, the initialization took 5 lines.  It would have been even
more if every object had to know about every other object.  If the
same sort of thing had to be written multiple times, it's a lot nicer
to put it all in one place so we don't have to repeat it.

To use this in your case, replace the call for lookForInst on the
object that you passed in with a call for lookForInst on one of the
member variables (like @a, @b, @c...).  You'll probably find that you
don't have to pass the objects in, so your code wil look much less
procedural.

--
Laurel Fan
http://dreadnought.gorgorg.org

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=3D Lesson 2: Containers, Blocks, and Iterators; Standard Types; More
About Methods

=3D=3D Reading

If you're using the paper or pdf 2nd edition, the reading is chapters
4-6, pages 40 to 80.

If you're using the online 1st edition, the reading is:

http://www.rubycentral.com/book/tut_containers.html
http://www.rubycentral.com/book/tut_stdtypes.html
http://www.rubycentral.com/book/tut_methods.html

With the last lesson, Akkana was wondering when yield and blocks were
useful, and Anne had asked about how objects could send messages to
other objects.  These readings will hopefully provide some more
information about these topics.

Here are two more pages that might be useful:

Ruby idioms: http://www.rubygarden.org/ruby?RubyIdioms
Provides a few elegant ways to do common things in Ruby.

Annotated Ruby docs: http://ruby.outertrack.com/
Read and leave comments and annotations on the standard documentation.

=3D=3D Homework

=3D=3D=3D Questions

0. Same as last time, is there anything you didn't understand?  would
   like to learn more about?

1. How many different ways can you think of to write the
   following string declaration code?
----
name =3D "Laurel"
----

   There are plenty of ways to answer this, so be creative :)

2. What are the 4 things you can specify when calling a method?  In
   what situations are each of them optional, not allowed, or
   mandatory?

3. What does this do?

(first, second, third) =3D "1 2 3".split(/ /)

p first + third

=3D=3D=3D Problems

1. Blocks and iterators:

Rewrite the findLongWords method below using iterators and blocks
instead of the for loop:

----
# Given an array of words, findLongWords returns a new array
# containing the words with more than 5 letters.
def findLongWords(words)
  longWords =3D Array.new()
  for i in 0...words.length
    if !words[i].nil? && words[i].length > 5 # long words have more
than 5 letters
      longWords << words[i]
    end
  end
  longWords
end

p findLongWords(['thisOneIsLong', 'short', 'howAboutThisOne' ])
----

Hint: look at the documentation for the Enumerable module:
http://www.ruby-doc.org/core/classes/Enumerable.html

2. Blocks and sort

Normally, if you call sort on an array of strings, it'll sort by their
lexical value (ie. alphabetically).  Write some code that will sort an
array of strings first by number of vowels (fewest first), and then by
lexical value (for strings of the same length.  For the sake of this
problem, let's say that a, e, i, o, and u are the only vowels.

For example:

Normal sort would do:

['dog', 'cat', 'aardvark', 'bird'].sort
#=3D> ['aardvark', 'bird', 'cat', 'dog']

Your code should return:

['bird', 'cat', 'dog', 'aardvark']

You can use the Enumerable.sort function:
http://www.ruby-doc.org/core/classes/Enumerable.html#M001944

Bonus: use Enumerable.sort_by:
http://www.ruby-doc.org/core/classes/Enumerable.html#M001945
(the example at the link above)

3. Implement some methods

Below is a skeleton class definition for the /proc information class
we talked about in the last lesson.  Implement the blank methods.

----
class ProcessInfo
  # initialize a ProcessInfo object with:
  # pid      process id
  # cmdline  complete command line of the process
  # cwd      name of the working directory of the process
  # exe      filename of the executable program
  # files    array of files that the process has open
  def initialize(pid, cmdline, cwd, exe, files)
    # Please implement
  end

  # calls the given block once for each open file, passing the file
  # name as a parameter.
  def each_open_file
    # Please implement
  end

  # add the provided file names to the process' list of open files
  def add_open_files(*new_files)
    # Please implement
  end

  # return a string representation of the process information
  def to_s
    # Please implement
  end
end


### test code

test_process =3D ProcessInfo.new(20,
                     "emacs -nw my_program.rb my_library.rb",
                     "/home/laurel",
                     "/usr/bin/emacs",
                     ["/home/laurel/my_program.rb",
"/home/laurel/my_library.rb"]);

print "Before adding files:\n"
print test_process.to_s
print "Process #{test_process.pid} has the following files open:\n"
test_process.each_open_file do |open_file|
  print " - #{open_file}\n"
end

test_process.add_open_files("/home/laurel/another.rb", "/home/laurel/more.r=
b")

print "\nAfter adding files:\n"
print test_process.to_s
print "Process #{test_process.pid} has the following files open:\n"
test_process.each_open_file do |open_file|
  print " - #{open_file}\n"
end

----

The output of the test code should look something like:

----
Before adding files:
20: emacs -nw my_program.rb my_library.rb
 cwd=3D/home/laurel, exe=3D/usr/bin/emacs, 2 open files
Process 20 has the following files open:
 - /home/laurel/my_program.rb
 - /home/laurel/my_library.rb

After adding files:
20: emacs -nw my_program.rb my_library.rb
 cwd=3D/home/laurel, exe=3D/usr/bin/emacs, 4 open files
Process 20 has the following files open:
 - /home/laurel/my_program.rb
 - /home/laurel/my_library.rb
 - /home/laurel/another.rb
 - /home/laurel/more.rb
----

Bonus: I don't think the constructor is very nice to use.  I have to
remember all of the arguments and what order they're in, so it's easy
to make a mistake and end up with the cmdline as the cwd, etc.  What
are some other ways you could write it?

--
Laurel Fan
http://dreadnought.gorgorg.org

From anne@wjh.harvard.edu  Sun Dec  4 02:58:52 2005
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Date: Sat, 3 Dec 2005 10:58:44 -0500 (EST)
From: Anne G <anne@wjh.harvard.edu>
To: <courses@linuxchix.org>
Subject: [Courses] [Ruby] Lesson 2: Iterators 
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Hi Laurel,

Thank you so much for helping with my example, so I only
have to grasp the ruby points.

I understood your example with the objecthelper. When I
tried to compile it, I got some error regarding my recursion
with lookforXs.

in `notEndofData?': stack level too deep (SystemStackError)
   from /Users/anne/Desktop/dudruby8d.rb:39:in lookforX'

I tried to use catch and throw, but it did not change the
error. How do I break from a recursion like mine?
Here is the method which calls lookforX with catch/throw

def getinfo
    # the first time we run this method, we are in a block,
    # and we store the data
        if self.notendofblock?
              @storeArr.push(writeline)
              self.increasind
              self.getinfo
    # after a while we reach the end of the block
    # and look for a new one
        else
              catch(:myrecursion) do
                   self.lookforX
              end
        end
end

And here is lookforX

def lookforX
         if self.notEndofData?
                # We found the keyword that starts a subject
                if self.trial?
                    @helper.getinfo    # go store some info
                    throw :myrecursion # break out
                # or we keep looking for the keyword
                else
                    self.lookforX
                end
         else   #end of file, we are done
                throw :myrecursion
         end
end

actually I have two recursions, lookforX method calls for
self.lookforX method, and getinfo calls for self.getinfo.
So maybe I need to break out of both recursions?

Is the use of recursions like this to be avoided?  my use of
catch and throw is not very elegant here, running across two
methods. Can it be used better? Is the alternative to use a
loop?




From anne@wjh.harvard.edu  Sun Dec  4 12:24:55 2005
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Date: Sat, 3 Dec 2005 20:24:48 -0500 (EST)
From: Anne G <anne@wjh.harvard.edu>
To: <courses@linuxchix.org>
Subject: Re: [Courses] [Ruby] Lesson 2: Iterators 
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I think I fixed the problem with the lookforX recursion,
--- the code never reached the throw command in my first try
because helper.getinfo moved to objectinfo1, objectinfo2,
and back to objectstore...
--- Even with this problem fixed, the getinfo recursion
reaches too many levels. getinfo calls getinfo through the
info objects, which calls getinfo...

def lookforX
         throw :myrecursion if self.trial?
         self.increaseind
end

def getinfo
     if self.notendofblock?  # we are in a block, store the data
              @storeArr.push(self.tokeep)
              self.increaseind
              self.getinfo
    else   # we reached the end of a block, look for a new one.
             catch(:myrecursion) do
                   while self.notendofData?
                        self.lookforX
                   end
                   break
              end
              @helper.getinfo if self.trial?
     end
end

What I wanted was three independent objects which did their
bit and told each other when to get started, but in the
actual implementation, it does not work I think because the
three objects are not actually independent. Each time we
call on an object, we tie a know which we have to untie at
some point.

On Sat, 3 Dec 2005, Anne G wrote:

> Hi Laurel,
>
> Thank you so much for helping with my example, so I only
> have to grasp the ruby points.
>
> I understood your example with the objecthelper. When I
> tried to compile it, I got some error regarding my recursion
> with lookforXs.
>
> in `notEndofData?': stack level too deep (SystemStackError)
>    from /Users/anne/Desktop/dudruby8d.rb:39:in lookforX'
>
> I tried to use catch and throw, but it did not change the
> error. How do I break from a recursion like mine?
> Here is the method which calls lookforX with catch/throw
>
> def getinfo
>     # the first time we run this method, we are in a block,
>     # and we store the data
>         if self.notendofblock?
>               @storeArr.push(writeline)
>               self.increasind
>               self.getinfo
>     # after a while we reach the end of the block
>     # and look for a new one
>         else
>               catch(:myrecursion) do
>                    self.lookforX
>               end
>         end
> end
>
> And here is lookforX
>
> def lookforX
>          if self.notEndofData?
>                 # We found the keyword that starts a subject
>                 if self.trial?
>                     @helper.getinfo    # go store some info
>                     throw :myrecursion # break out
>                 # or we keep looking for the keyword
>                 else
>                     self.lookforX
>                 end
>          else   #end of file, we are done
>                 throw :myrecursion
>          end
> end
>
> actually I have two recursions, lookforX method calls for
> self.lookforX method, and getinfo calls for self.getinfo.
> So maybe I need to break out of both recursions?
>
> Is the use of recursions like this to be avoided?  my use of
> catch and throw is not very elegant here, running across two
> methods. Can it be used better? Is the alternative to use a
> loop?
>
>
>
> _______________________________________________
> Courses mailing list
> Courses@linuxchix.org
> http://mailman.linuxchix.org/mailman/listinfo/courses
>


From jennyw@dangerousideas.com  Fri Dec  9 18:56:32 2005
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Anne G wrote:

>What I wanted was three independent objects which did their
>bit and told each other when to get started, but in the
>actual implementation, it does not work I think because the
>three objects are not actually independent. Each time we
>call on an object, we tie a know which we have to untie at
>some point.
>  
>
Hi, Anne,

I went back and read through your e-mails ... I wasn't sure what you're 
trying to accomplish with the three objects. Is this an abstract example 
or is there a practical application? It looked very abstract to me, so 
it was hard to figure out what you're trying to accomplish.

Going back, I see you were asking how to send messages to objects. You 
just do it like this ... object.message. For example,

fruits = ['apple', 'pear', 'banana'] #  an array of fruits
fruits.first     # send the message #first to the fruits object. it 
returns a string: 'apple'
fruits.first.class # you can also send two messages in a row -- for 
example, this sends #class to 'apple'. It'll return the class, String.

You also asked how can you can have two objects that do things and ask 
each other to do something. I see that you have the objects calling each 
other, and some recursive methods, but this is all implementation -- 
what I'm not clear on is the problem that this is the proposed solution 
for. I don't think this is so much a Ruby thing as it is a design 
issue.  It could well be that there's a design pattern that matches 
exactly what you want to do -- if we figure out what that is, it should 
be a lot easier to show it in Ruby.  I guess the first step might be to 
come up with a practical example (i.e. a user story). You might have 
done this, of course, and I may have missed it, so apologies if that's so.

Good luck!

Jen


From anne@wjh.harvard.edu  Fri Dec  9 22:43:54 2005
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Date: Fri, 9 Dec 2005 06:43:44 -0500 (EST)
From: Anne G <anne@wjh.harvard.edu>
To: jennyw <jennyw@dangerousideas.com>
Subject: Re: [Courses] [Ruby] Lesson 2: Iterators
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HI,

Thank you for your response

> I don't think this is so much a Ruby thing as it is a
> design issue.
Yes, I want to understand object oriented programming
thinking. I started with objective C and cocoa, but I was
frustrated with it and not learning any OOP. Ruby is so much
easier, I can get to the methodology.

> Is this an abstract example or is there a practical
> application?
What I want to learn is abstract, the example I chose to
learn with - which might not be the best - is concrete.

As I understand it, in procedural programming, which is what
I have been doing, I write code thinking all along of time.
The code does this, then this, then this... in a thread.

In OO programming, it is more like a state machine in
digital electronic. All I need to know is the state of the
object, and what it will do if it gets some info. So I
should be able to define things locally only, and the whole
thing should work based on logic more than time.

The concrete example I took is an archive file with 20000
lines of data from 200 subjects in an experiment. The
procedure way, I read the file line by line, and with ifs,
switches etc, I tell it what to do to extract the info I
want from the data file.  The OO P way, I have three
objects, each specializing in a particular aspect of the
data, and they call on each other once they are done with
their part.

> fruits = ['apple', 'pear', 'banana'] # an array of
> fruits fruits.first # send the message #first to the
> fruits object. it returns a string: 'apple'

This is how objects and messages are first explained. But my
question is at one level of abstraction higher: In most
examples, the methods are defined in a class when the
instances of the objects are not yet defined.

In my case, How will the object which stores the actual
subject data tell the object which stores the subject's id
that the next line in the file is for it to process, when
neither object is around at the time of the method
definition.

Laurel came up with a class object @helper which will
contain the instantiated object to be called at execution.

This worked very well, getdata calls getinfo1 which calls
getinfo2 which calls getdata ad infinitum. The problem I
encounted is that ad infinitum is not supported by my
implementation of Ruby, I got an error message, too many
levels (each repeat call on getdata is a level).

Of course I can find ways to write the code more efficiently
to avoid the limit, but by calling a method for each line of
code, I encountered a limit, and the fact that the limit
exists is what bothers me. That means I have to make sure
the whole program is done is so many calls.  This is not a
stable timeless implementation. It could not run on live
data that kept coming and coming.

It is probably because I am doing something wrong
in my object communication, but I don't know what it is.

---------------------------------------------------------

as for the general problem as to how to get objects to
communicate, here is an answer I received, which I haven't
figured out how to use in my own 3 object example.

Partly, most objects communicate only with objects they
create and the object that created them.

class A
  def initialize
    arr=[1,2,3,4]
    arr.last
  end
  def ask
    return arr.first
  end
end

a=A.new
last=a.ask

Here the object we are currently in creates an object a of
class A, it communicates with this object with a.ask. The
object a itself creates an Object arr and also communicates
with that. This is the way most object communicate with each
other.

If you need two object (A and B) that are created by a third
object (C)  to communicate with each other then you are
probably doing something wrong (although not always) and it
might have been better if Object A had created object B
instead of letting Object C create both.




From laurel.fan@gmail.com  Sat Dec 10 04:13:26 2005
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To: Anne G <anne@wjh.harvard.edu>
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On 12/9/05, Anne G <anne@wjh.harvard.edu> wrote:
> This worked very well, getdata calls getinfo1 which calls
> getinfo2 which calls getdata ad infinitum. The problem I
> encounted is that ad infinitum is not supported by my
> implementation of Ruby, I got an error message, too many
> levels (each repeat call on getdata is a level).
>
> Of course I can find ways to write the code more efficiently
> to avoid the limit, but by calling a method for each line of
> code, I encountered a limit, and the fact that the limit
> exists is what bothers me. That means I have to make sure
> the whole program is done is so many calls.  This is not a
> stable timeless implementation. It could not run on live
> data that kept coming and coming.

Now I think I understand a bit more of what the problem is.

Recursion (methods calling themselves) might not be the best solution
for data that keeps coming continuously.  Each recursive method call
causes a little bit of overhead (it needs to keep track of every
method currently running), and this can add up over time.

It's also possible that there's a bug in the code causing an infinite
recursion loop.

Without seeing all of your code, it's hard to tell what exactly the
problem is, or whether there would be a better way to implement it
without recursion.  Would you be willing to post the whole thing to
the list?

--
Laurel Fan
http://dreadnought.gorgorg.org

From anne@wjh.harvard.edu  Sat Dec 10 06:48:13 2005
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From: Anne G <anne@wjh.harvard.edu>
To: Laurel Fan <laurel.fan@gmail.com>
Subject: Re: [Courses] [Ruby] Lesson 2: Iterators
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HI

> Without seeing all of your code, it's hard to tell what
> exactly the problem is, or whether there would be a
> better way to implement it without recursion.  Would you
> be willing to post the whole thing to the list?

Yes of course. But at this point my question is more
conceptual:

I changed the code so that within each block of data, I use
a loop. This way, I only run getdata, getinfo1 and get info2
once per subject, and so the maximum level of recursion is
the number of subjects, around 200, a number which ruby can
handle, and there is no error.

> Each recursive method call causes a little bit of
> overhead (it needs to keep track of every method
> currently running), and this can add up over time.

I assume that OOP can handle open ended, real time
situations. So a working design would need to go back
to a neutral point from time to time to clear out the
methods running.

In my case,
getdata finds a header
getdata  calls getinfo1,
getinfo1 calls getinfo2
getinfo2 calls getdata
getdata stores the subjectdata.

At this point there is a clear breaking point, and I ought
to go back to neutral. Is there a ruby command which I could
use to say go back to top level, forget about tracking down
all those methods?

anne
On Fri, 9 Dec 2005, Laurel Fan wrote:

> On 12/9/05, Anne G <anne@wjh.harvard.edu> wrote:
> > This worked very well, getdata calls getinfo1 which calls
> > getinfo2 which calls getdata ad infinitum. The problem I
> > encounted is that ad infinitum is not supported by my
> > implementation of Ruby, I got an error message, too many
> > levels (each repeat call on getdata is a level).
> >
> > Of course I can find ways to write the code more efficiently
> > to avoid the limit, but by calling a method for each line of
> > code, I encountered a limit, and the fact that the limit
> > exists is what bothers me. That means I have to make sure
> > the whole program is done is so many calls.  This is not a
> > stable timeless implementation. It could not run on live
> > data that kept coming and coming.
>
> Now I think I understand a bit more of what the problem is.
>
> Recursion (methods calling themselves) might not be the best solution
> for data that keeps coming continuously.  Each recursive method call
> causes a little bit of overhead (it needs to keep track of every
> method currently running), and this can add up over time.
>
> It's also possible that there's a bug in the code causing an infinite
> recursion loop.
>
> Without seeing all of your code, it's hard to tell what exactly the
> problem is, or whether there would be a better way to implement it
> without recursion.  Would you be willing to post the whole thing to
> the list?
>
> --
> Laurel Fan
> http://dreadnought.gorgorg.org
>


From anne@wjh.harvard.edu  Sat Dec 10 22:10:47 2005
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To: Laurel Fan <laurel.fan@gmail.com>
Subject: Re: [Courses] [Ruby] Lesson 2: Iterators
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 > Recursion (methods calling themselves) might not be the
> best solution for data that keeps coming continuously

This morning I got the implications of Laurel's comment:
If I want code which runs continuously, or some such, I need
to make sure that the structure of the object connections
does not contain a loop.

In my case, I ought to be able to pass the control from
object getdata to object info1 to object info2. And there it
stops.

If info2 does not call anyone, control gets back to getdata
BY ITSELF! and it can go on with its task. getdata thus
becomes the neutral state object I was talking about.

In turms of diagram, it looks like an octopus, with
tantacles going in different directions.

Thank you so much for your help. We don't have /proc on the
mac so I can't work on that part of lesson 2.

anne


From anne@wjh.harvard.edu  Sun Dec 18 06:45:10 2005
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From: Anne G <anne@wjh.harvard.edu>
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Subject: [Courses] [Ruby] Lesson 2: Containers, Blocks, and Iterators  
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Questions
1. write the following string declaration code?
test = "thank you"
test2='Laurel'
test3=String.new("For")
text4="y"+"o"+"u"+"r"


2. What are the 4 things you can specify when calling a
method?
object it applies to: if not specified, applies to self.
name of method
arguments
block

* to indicate that the arguments is to be read as an array?
& associated block converted to proc object?

problem 1
----------
# Given an array of words, findLongWords returns a new array
# containing the words with more than 5 letters.

def findLongWords(words)
  longWords = Array.new()
  words.each { |wrd|  longWords.push(wrd) if (wrd.length>5)
}
  return longWords
end
p findLongWords(['thisOneIsLong', 'short', 'howAboutThisOne'
])

solution with enumerable

def findLongWords(words)
  words.find_all {|wrd| wrd.length>5}
end
p findLongWords(['thisOneIsLong', 'short', 'howAboutThisOne'
])

problem2
---------
arr=%w{ dog cat aardvark bird}
puts "simple sort"
puts arr.sort
puts "new sort"
puts arr.sort_by{|wrd| (wrd.count("aeiou") + 0.01*wrd[0])}

questions: yield and blocks?
-----------------------------------
the simple block formulation can be understood as is, but I
don't really get yield, and blocks...

Someone gave the following example on comp.lang.ruby

class List
   def add(obj)
     @first = [@first,obj]
   end

   def each
     e = @first
     while e
       yield e[1]
       e = e[0]
     end
   end
end

l = List.new
l.add("hello")
l.add("world")
l.add("of")
l.add("beauty")

l.each do |s|
   puts s
end

It puts the words in reverse order, but I don't understand
why e[1] turns out to be the last word in the
sequence? and why the sequence shortens each times
it goes through the while loop.

Since I don't understand the code, I haven't really
figured out what the yield does, why it is interesting

------------------------------------------------------------
Here are the other examples for those interested in yield
that I would like to study next to try to get the point of
yield.

Example B): Traversing a data structure recursively:

class Array
   def traverse_rec
     for e in self do
       if e.kind_of? Array
         e.traverse_rec
       else
         yield e
       end
     end
   end
end

[ [1,2] [1,3,[4,[5] ],2,[3,4] ] ].traverse_rec do |el|
    puts el;
end

outputs all elementes of the tree recursively.
(The tree is implemented as an array of (possible arrays of
  (possible ....))... )

------------------------------------------------------------
Example C)

Do something with each element of the a data structure
(minor variation of example 1):

class List
   def add(obj)
     @first = [@first,obj]
   end

   def map
     e = @first
     while e
       e[1] = yield e[1]
     end
   end
end

l = List.new

l.add("hello")
l.add("world")

l.map do |s|
   s.length
end

Each element of the list is replaced by its length.

-------------------------------------------------------------
Example D)

Do something according to a dynamic criterion

(Sum up all elements of a list conditionally)

class List
   def add(*objs)
     objs.each do |obj|
        @first = [@first,obj]
     end
   end

   def sum_if
     e = @first
     sum = 0;
     while e
       sum += e[1] if yield e[1]
     end
   end
end

l = List.new
l.add(1,3,4,5,6,2,1,6);

l.add_if do |i|
   (i%3)==0
end

The last function sums all elements of the list which
are divisible by 3.

I hope it gives you some insides about the power
of yield.
Regards, Christian






From anne@wjh.harvard.edu  Sun Dec 18 17:54:35 2005
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I have a hard time with the book. its song example
completely turns me off, it is much too wordy and too long
to be of any use to me, and it keeps poping out everywhere.

Here is an explanation of yield which works better for me

Think of a block as an anonymous subroutine. Instead of
saying
def func(x,y)
  # ... do stuff
end
it goes

{ |x,y|
  # ... do stuff

}

yield is just the way you call the block passed to the
function.  If you have a C/C++ background, it might help to
think of blocks as function pointers and yield as
dereferencing a function pointer.  Yield is similiar to a
callback function.  Even closer to function pointers in
C/C++ is a proc object.

myproc = proc { |x,y|
  puts "x: #{x}, y #{y}"

}

# You can accept these objects as parameters to functions
def func(x,y,p)
  p.call(x,y)
end

func(1,2,myproc)

Using yield is just a more convenient way to perform the
same thing.
The yield version of the above might go as follows:

def func(x,y)
  if( block_given?)
    yield(x,y)
  end
end

func(1,2) { |x,y|
  puts "x: #{x}, y #{y}"

}






From anne@wjh.harvard.edu  Wed Dec 21 19:00:18 2005
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>    def add(obj)
>      @first = [@first,obj]
>    end

I got it. In matlab, this would append the obj to an array.
Here @first is a new array, with the old @first as an
element, and obj as a second element. Since this is not an
array, the length method does not work.

--------------------------------------------

It seems that yield/block can help emphasize the goal of the
transaction, and hide the mechanics to do it:  When you see
a method with a puts block, you know this line is printing
some info

I also found it useful as a short cut when there is a
process that is the same to support different actions. For
example I rewrote my data reading program with blocks

getinfo {|line| @info1Arr.push("'" +line[6] + "'")}
increaseind
getinfo {|line| @info2Arr.push(line[6])}
increaseind
getinfo {|line| @dataArr.push(line[0]+","+line[2]+","+line[4])}

In this way the same method getinfo was used to extract
different columns in the data file, depending on the block
formula.

anne



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From: chantal@antenna.nl
To: laurel.fan@gmail.com
Subject: Re: [Courses] [Ruby] Lesson 0: Installing, References,
        and your first homework assignment]
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Hi Laurel, sorry for the late reply, here's what I have so far, I started=
 on the
bonus question but it's not finished yet :-)

1. Defining classes: photo gallery. Think about what classes you
would need to define to write a web photo gallery application. For
now, don't think of the actual implementation details of handling
web requests, displaying images, etc. Obviously you'll need to
represent a photo. What attributes does it have? What other
objects do you need?
post what you have done)

attributes of a photo are:

- width
- height
- filename
- subject
- date

2. Defining classes: /proc. (This might not be as interesting for
windows users). On unix, the /proc filesystem is a virtual
filesystem containing information about the running processes
(among other things). It contains a directory for each running
process, which contains information about the process, such as the
command line, the amount of memory it's using, etc). <A0>Define a set
of classes to represent the process data in /proc.

every file in the process directories could be considered a class, althou=
gh I
don't really know what they all mean.
I will pick a few of them to use in the exercise:

- status, I guess the attributes are everything that is listed in the fil=
e
/proc/$processid/status
- cmdline, its attribute is the (current?) init level
- statm,  The status of the memory in use by the process, its attributes:
         Total program size, in kilobytes.
         Size of memory portions, in kilobytes.
         Number of pages that are shared.
         Number of pages that are code.
         Number of pages of data/stack.
         Number of library pages.
         Number of dirty pages.
(I found some info about the proc dir here:
http://www.redhat.com/docs/manuals/enterprise/RHEL-3-Manual/ref-guide/s1-=
proc-di
rectories.html)

Chantal

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