If you are speaking at RubyConf this year, we have a special opportunity for you.

Are You Speaking at RubyConf 2008?

If so, congratuations! And have we got a deal for you …

Wednesday evening, Nov 5, at 6:00 pm, (that’s the night before the conference) we are inviting all speakers to a special training session. I’m going to be sharing some ideas for putting together and delivering a good presentation.

After my talk, Patrick Ewing and Adam Keys are geared up to do some Powerpoint Karaoke with everyone there. I’m not even sure what Powerpoint Karaoke is, but it sounds like fun.

I hope to see everyone there.

Update (4/Nov/08)

I’ve talked to Adam today. He says that Patrick isn’t going to able to make RubyConf this year, but we will be ready to roll with Powerpoint Karaoke anyways.

Update (5/Nov/08)

It looks like the speakers training will be in the Olympic Room tonight. The Olympic Room is on the same floor as the registration desk. Go to the left past the elevators and turn right down that hall (or ask someone who looks like they know what they are doing).

I’ve received a lot of requests for my old articles …

The Article Section has been Restored

When I changed to my new hosting machine, I moved all my blog posts but didn’t move any of the articles. Of course I intended to move them eventually but never got around to it.

A lot of people have been asking for this article or that presentation, or pointing out that a number of old bookmarked links are no longer any good. So due to popular demand the Articles and Presentations section of onestepback.org is now restored.

Enjoy

I’ve gone without comments on this blog for a long time …

Comments via Disqus

I’ve gone through several commenting systems for this blog over time. First was the really cool TagSurf application that allowed commenting on about any web page on the internet arbitrary tags. Unfortunately, TagSurf died a (in the words of its creator) “well deserved” death.

Then I tried a wiki for comments. That worked pretty good (aside from spam issues), but setting up a new page for comments for each new post was just too much hassle.

Now I’m trying Disqus for comments. It only took an hour or so to integrate Disqus with my ancient blogging engine (anyone else still using Rublog?).

Kick the tires and see how it works. If you have feedback … well, just leave a comment.

I guess this means I’ll have to start writing some real content here so there will be something worth commenting on … let’s see if there is anything I feel like ranting about …

(Oh, and a hat tip to Ryan Briones for pointing out Disqus when I was ready to go out and implement something from scratch.)

The is now a RedMine setup for Rake, FlexMock and Builder.

RedMine

As part of an effort to get better control of changes to the my open source projects, I’ve setup a RedMine issue tracking site for Rake, FlexMock and Builder. You can find it at http://onestepback.org/redmine.

I am changing host for the One Step Back blog.

It’s Time to Move

This is just a quick little post to let you know that the One Step Back blog is moving. In fact, it has already moved. But don’t worry, we aren’t going far.

Originally this blog was hosted on a shared co-op system run by N2Net. It was dirt cheap and easy to maintain. The down side was that support was sporadic. As the hardware has aged, the Co-op has decided to let the current system run until the hardware dies, and then disolve the co-op.

Today there are tons more hosting opportunities available than there were when the co-op was first formed. I’m now leasing a Linode node and running the blog and other associated software from there. Its almost as inexpensive and the co-op and uptime should be better.

Write now the blog has been moved. As time passes I’ll move the article archive as well. Let me know if anything looks amiss.

—Jim Weirich

Tagged

Looks like Joe O’Brien tagged me for answers to the following questions. He, in turn, was tagged by Josh Owens, who in turn was tagged by Jeff Blankenburg. It looks like Sarah Dutkiewicz and Micheal Eaton started this.

OK, sounds like fun. Here goes.

How old were you when you started programming?

I was introduced to programming in high school by reading a book on the topic. The book taught me how to write machine code for a strange decimal-based machine. Unfortunately, there was no actual computer involved in the process. Shoot, who had computers back then? Certainly not our high school (the personal computers? not invented yet!)

In college, I learned a smattering of FORTRAN. Just enough to drive a Calcomp plotter to plot data from my undergraduate physics courses. But didn’t really get into programming until my junior year in college. (Story continued in next question)

How did you get started in programming?

So, I was planning out the courses for my junior year in college and I had a hole in my math courses. The math class I needed was not offered that semester, so my adviser suggested taking a computer programming course. He said it would be useful and, who knows, I might enjoy it.

So I signed up for an introduction to FORTRAN course, figuring it would be easy because I already knew a little bit of FORTRAN. I show up on the first day of class and after a few preliminaries the instructor jumps right into some code, that looked like this:

  (de member (pip deck) (cond
    ((null deck) nil)
    ((eq pip (car deck)) t)
    (t (member pip (cdr deck)))))

I remember scratching my head and thinking this was the strangest FORTRAN I had ever seen. I was totally confused for about three days, then something clicked on the third day of class. I suddenly “got” what the instructor was trying to get across and it all made perfect sense.

If you haven’t figured it out yet, the instructor taught us Lisp as part of an introduction to FORTRAN. The instructor turned out to be Daniel Friedman, the author of The Little Lisper, and was well known in the Lisp community. That small exposure to Lisp hooked me on programming from that point on. I took as many CompSci courses as I could in my remaining year and a half in college. I eventually graudated with a BS in Physics, but had a strong background in Computer Science as well.

What was your first language?

Technically, FORTRAN was my first language. But Lisp is the language I fell in love with and is what got me hooked on programming.

What was the first real program you wrote?

I have a very clear memory of the very first program I wrote professionally. The reason it is so clear is that this was the first program I wrote that was intended for actual use by someone who wanted it. Everything else up to that time was done for my own personal enjoyment or to satisfy some course requirement.

The program calculated the “critical angles” of “pieces”. I was given the requirements by Anne Exline, a senior programmer, and proceeded to write the program to spec. It took a few days, but when I was done I showed the result to Anne and she was pleased with the result.

The funny thing is that I had no idea what a “piece” was nor what was so critical about the angles I was calculating. I was so excited about writing an actual program that I did not ask until the software was done. When asked, Anne just looked at me funny and said “Rocket Pieces”. When Cape Canaveral lauches a rocket, they track it very carefully to make sure it stays on course. If it strays, the range safety officer is required to activate the self destruct. The critical angles are those angles that would cause the “rocket pieces” to land outside the safety area of the flight path.

So, my very first professional program was not only useful, it might actually save lives.

What languages have you used since you started programming?

Languages I have used as part of my professional career (in roughly chronological order) include FORTRAN, various assembly languages, FORTH, C, PL/M, C++, Java, Ruby.

Languages I have used in addition to those mentioned above: Pascal, Perl, Eiffel, and Lisp/Scheme.

Languages I can read, but never wrote anything significant in them: Ada, Python, Erlang, Smalltalk, SNOBOL, Algol, Pascal.

What was your first professional programming gig?

I was hired by the RCA Missile Test project in Cape Canaveral, Florida as a Near Real Time Analyst. Duties included programming various launch related software (e.g. the critical angle program mentioned above) and working launch support.

The launch support was the “Near Real Time” part of the job description. From the moment a rocket is launched until it reaches orbital velocity, any malfunction could cause it to fall back to earth. During this initial portion of the launch, the launch is monitored in “real-time” so that we know exactly where it would land if the engines were to cut off NOW. Trajectory calculations had to be done in fractions of a second and updated constantly in real time.

After the rocket reaches oribital velocity (usually somewhere between 8 and 14 minutes into its flight), it won’t fall back to earth. At this point the real time trajectory program is shut down and the near real time program is started. The near real time program can take a few minutes to calculate a more exact orbital prediction and then send that prediction to downrange radars (e.g. the the Ascension Island station) that won’t see the rocket until about 20 minutes after launch. It was the job of the Near Real Time analyst to run that program and provide oribital predictions for downrange station.

If there is one thing you learned along the way that you would tell new developers, what would it be?

Find something that you enjoy and do that. Life is too short to work in a job that you dislike.

What’s the most fun you’ve ever had … programming?

Oh, the fun I have had. This story still makes me smile.

My first computer was a single board Z80 microcomputer with 4 KB of memory. I wrote a small FORTH-like interpreter for it and hacked a version of the animal game in FORTH. The animal game is a program that plays 20 questions to figure out what animal you are thinking of. It constructs a binary tree where each node is a question and the subtrees are the yes and no answers to the question. To play the game, all the program does is walk the tree, ask the question at the current node and follow either the YES branch or the NO branch as appropriate.

If the program guesses wrong, it will ask you for your animal and a question that will distinguish your animal from the one it guessed. It then adds your question to the tree. By this extremely simple mechanism, it is able to expand its knowledge base. (see Ruby Quiz #15 for more details).

I had just finished the program and had seeded it with a single animal, a mouse. I turned to my wife and asked her to play the game. She thinks of an animal and starts the program, which immediately asked her “Is it a mouse?”. She turned to me with surprise and said “How did it know?”. Of course, the animal she picked was a mouse.

I don’t think I have ever impressed anyone with my programming skills as much as she was impressed with that game.

Who’s up next?

I’m tagging the following people. Remember, this is entirely voluntary so don’t feel obligated to answer. But I’m betting the answers are interesting:

• Chris Nelson
• Mike Clark
• Giles Bowkett
• Mark Windholtz
• Glenn Vanderburg

Conference Summary Video

Wow, what a great conference! There was a lot of energy flowing at RailsConf this year. Overall I’d rate this year as head and shoulders above last year. I’m not going cover much here, but will direct you attention to a Rails Envy VideoCase that Greg Pollack put together. The video is a series of very short interviews with a number of presenters giving summaries of their own talks. The only downside with the video is that I wish it was available before the conference. I see there were a number of interesting talks that I missed.

Followup on the “Modelling Dialogue”

Joe O’Brien, Chris Nelson and myself did a dialogue style presentation on the difference between object modelling and data modelling. The most common question I got after the talk was requests for book titles to learn more about object oriented modelling. Here are the books that Joe, Chris and I have recommended:

• Domain Driven Design—Eric Evans
• AgileSoftware Development, Principles, Patterns, and Practices—Bob Martin
• Refactoring: Improving the Design of Existing Code—Martin Fowler

The Musician’s Birds of a Feather gathering at RailsConf was great. We had a room full people, two guitars, a ukulele, a flute, several harmonicas and an improvised drum set. Unfortunately, one of the guitars was an electric travel guitar which had a dead battery, therefore no way to really hear it.

However, the other guitar was a nice Epiphone accoustic which was passed from player to player. It became the quickly became the basis for most of the music performed that night.

I want to thank Artichoke Community Music for supplying the guitar. Travelling with a guitar by plane is a big pain, so I arrived with nothing to bring to the music BOF. I called several local music stores looking for a guitar that I could rent for an evening. Artichoke music said they had a “not-for-profit” guitar that they would let me borrow for a day. Not many stores would do that for an out-of-town stranger.

So, if you’re in Portland looking for a good guitar store, check out the great people at Artichoke Community Music.

Joe O’Brien and I will be leading another Test Driven Studio in Denver, June 9-11.

Testing, Colorado, June … What’s not to like?

About 8 years ago I come upon a technique that radically changed the way I developed code. I was reading Martin Fowler’s “Refactoring” book and came across this paragraph:

“Whenever I do refactoring, the first step is always the same. I need to build a solid set of tests for that section of code. The test are essential because even though I follow refactorings structured to avoid most of the opportunities for introducing bugs, I’m still human and still make mistakes. Thus I need solid tests.” —Martin Fowler

Chapter 4 of “Refactoring” was my first introduction to JUnit and got me interested in “Test First Design” (what we now tend to call “Test Driven Development”). Although I wrote good code before, the confidence I had in my code took a dramatic leap forward after I started adopting TDD practices.

On June 9 through 11, Joe O’Brien and I will have the pleasure of leading the next Pragmatic Programmer’s Test-Driven Development with Rails Studio. in Denver. We will have an opportunity to share with you some of our experiences in using TDD with Ruby and Rails.

There are still seats available, so its not too late to sign up. More information is available here.

I stumbled across this and it got me thinking …

Update

I’ve updated the Textile formatter on the site and the code for this entry is now displaying correctly. The previous version was swalling the == operators in the code.

Lisp 1.5 Programmer’s Manual

I stumbled across this in Bill Clementson’s blog and remembered using the Lisp 1.5 Prgrammers manual from the college years. I have strong memories of pouring over that particular page in the manual and attempting to understand all the nuances.

If you’ve never read the Lisp 1.5 Programamers Manual, page 13 is the guts of a Lisp Interpreter, the “eval” and “apply” functions. It is written in Lisp, although the notation used is a bit funky. The entire interpreter (minus two utility functions) is presented on a single page of the book. Talk about a concise language definition!

In Ruby?

I had often thought about implementing a Lisp interpreter, but back in the “old days”, the thought of implementing garbage collection and the whole runtime thing was a bit daunting. This was in the day before C, so my implementation language would have been assembler … yech.

But as I was reviewing the page, I realized that with today’s modern languages, I could problably just convert the funky M-Expressions used on page 13 directly into code. So … why not?

The Code

Here is the complete Ruby source code for the Lisp interpreter from page 13 of the Lisp Programmers manual:

  # Kernel Extensions to support Lisp
  class Object
    def lisp_string
      to_s
    end
  end

  class NilClass
    def lisp_string
      "nil" 
    end
  end

  class Array
    # Convert an Array into an S-expression (i.e. linked list).
    # Subarrays are converted as well.
    def sexp
      result = nil
      reverse.each do |item|
        item = item.sexp if item.respond_to?(:sexp)
        result = cons(item, result)
      end
      result
    end
  end

  # The Basic Lisp Cons cell data structures.  Cons cells consist of a
  # head and a tail.
  class Cons
    attr_reader :head, :tail

    def initialize(head, tail)
      @head, @tail = head, tail
    end

    def ==(other)
      return false unless other.class == Cons
      return true if self.object_id == other.object_id
      return car(self) == car(other) && cdr(self) == cdr(other)
    end

    # Convert the lisp expression to a string.
    def lisp_string
      e = self
      result = "(" 
      while e
        if e.class != Cons
          result << ". " << e.lisp_string
          e = nil
        else
          result << car(e).lisp_string
          e = cdr(e)
          result << " " if e
        end
      end
      result << ")" 
      result
    end
  end

  # Lisp Primitive Functions.

  # It is an atom if it is not a cons cell.
  def atom?(a)
    a.class != Cons
  end

  # Get the head of a list.
  def car(e)
    e.head
  end

  # Get the tail of a list.
  def cdr(e)
    e.tail
  end

  # Construct a new list from a head and a tail.
  def cons(h,t)
    Cons.new(h,t)
  end

  # Here is the guts of the Lisp interpreter.  Apply and eval work
  # together to interpret the S-expression.  These definitions are taken
  # directly from page 13 of the Lisp 1.5 Programmer's Manual.

  def apply(fn, x, a)
    if atom?(fn)
      case fn
      when :car then caar(x)
      when :cdr then cdar(x)
      when :cons then cons(car(x), cadr(x))
      when :atom then atom?(car(x))
      when :eq then car(x) == cadr(x)
      else
        apply(eval(fn,a), x, a)
      end
    elsif car(fn) == :lambda
      eval(caddr(fn), pairlis(cadr(fn), x, a))
    elsif car(fn) == :label
      apply(caddr(fn), x, cons(cons(cadr(fn), caddr(fn)), a))
    end
  end

  def eval(e,a)
    if atom?(e)
      cdr(assoc(e,a))
    elsif atom?(car(e))
      if car(e) == :quote
        cadr(e)
      elsif car(e) == :cond
        evcon(cdr(e),a)
      else
        apply(car(e), evlis(cdr(e), a), a)
      end
    else
      apply(car(e), evlis(cdr(e), a), a)
    end
  end

  # And now some utility functions used by apply and eval.  These are
  # also given in the Lisp 1.5 Programmer's Manual.

  def evcon(c,a)
    if eval(caar(c), a)
      eval(cadar(c), a)
    else
      evcon(cdr(c), a)
    end
  end

  def evlis(m, a)
    if m.nil?
      nil
    else
      cons(eval(car(m),a), evlis(cdr(m), a))
    end
  end

  def assoc(a, e)
    if e.nil?
      fail "#{a.inspect} not bound" 
    elsif a == caar(e)
      car(e)
    else
      assoc(a, cdr(e))
    end
  end

  def pairlis(vars, vals, a)
    while vars && vals
      a = cons(cons(car(vars), car(vals)), a)
      vars = cdr(vars)
      vals = cdr(vals)
    end
    a
  end

  # Handy lisp utility functions built on car and cdr.

  def caar(e)
    car(car(e))
  end

  def cadr(e)
    car(cdr(e))
  end

  def caddr(e)
    car(cdr(cdr(e)))
  end

  def cdar(e)
    cdr(car(e))
  end

  def cadar(e)
    car(cdr(car(e)))
  end

An Example

And to prove it, here’s an example program using Lisp. I didn’t bother to write a Lisp parser, so I need to express the lists in standard Ruby Array notation (which is converted to a linked list via the “sexp” method).

Here’s the ruby program using the lisp interpreter. The Lisp system is very primitive. The only way to define the function needed is to put them in the environment structure, which is simply an association list of keys and values.

  require 'lisp'

  # Create an environment where the reverse, rev_shift and null
  # functions are bound to an appropriate identifier.

  env = [
    cons(:rev_shift,
      [:lambda, [:list, :result],
        [:cond,
          [[:null, :list], :result],
          [:t, [:rev_shift, [:cdr, :list],
              [:cons, [:car, :list], :result]]]]].sexp),
    cons(:reverse,
      [:lambda, [:list], [:rev_shift, :list, nil]].sexp),
    cons(:null, [:lambda, [:e], [:eq, :e, nil]].sexp),
    cons(:t, true), 
    cons(nil, nil)
  ].sexp

  # Evaluate an S-Expression and print the result

  exp = [:reverse, [:quote, [:a, :b, :c, :d, :e]]].sexp

  puts "EVAL: #{exp.lisp_string}" 
  puts "  =>  #{eval(exp,env).lisp_string}" 

The program will print:

$ ruby reverse.rb
EVAL: (reverse (quote (a b c d e)))
  =>  (e d c b a)

All I need to do is write a Lisp parser and a REPL, and I’m in business!

The Example in Standard Lisp Notation

If you found the Ruby-ized Lisp code hard to read, here is the reverse funtions written in a more Lisp-like manner.

(defun reverse (list)
  (rev-shift list nil))

(defun rev-shift (list result)
  (cond ((null list) result)
        (t (rev-shift (cdr list) (cons (car list) result))) ))